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Consciousness

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https://en.wikipedia.org/wiki/Consciousness

Contents

1 Inter-disciplinary perspectives

2 Etymology

3 Dictionary definitions

4 Philosophy of mind

5 Scientific study

6 Medical aspects

7 Stream of consciousness

8 Spiritual approaches

9 See also

10 References

11 Further reading

12 External links

Not to be confused with Conscientiousness or Conscience.

This article is about cognition. For other uses, see Consciousness (disambiguation) and Conscious (disambiguation).

Representation of consciousness from the seventeenth century by Robert Fludd, an English Paracelsian physician

Consciousness at its simplest is "sentience or awareness of internal or external existence".[1] Despite centuries of analyses, definitions, explanations and debates by philosophers and scientists, consciousness remains puzzling and controversial,[2] being "at once the most familiar and most mysterious aspect of our lives".[3] Perhaps the only widely agreed notion about the topic is the intuition that it exists.[4] Opinions differ about what exactly needs to be studied and explained as consciousness. Sometimes it is synonymous with 'the mind', other times just an aspect of mind. In the past it was one's "inner life", the world of introspection, of private thought, imagination and volition.[5] Today, with modern research into the brain it often includes any kind of experience, cognition, feeling or perception. It may be 'awareness', or 'awareness of awareness', or self-awareness.[6] There might be different levels or "orders" of consciousness,[7] or different kinds of consciousness, or just one kind with different features.[8] Other questions include whether only humans are conscious or all animals or even the whole universe. The disparate range of research, notions and speculations raises doubts whether the right questions are being asked.[9]

Examples of the range of descriptions, definitions or explanations are: simple wakefulness, one's sense of selfhood or soul explored by "looking within"; being a metaphorical "stream" of contents, or being a mental state, mental event or mental process of the brain; having phanera or qualia and subjectivity; being the 'something that it is like' to 'have' or 'be' it; being the "inner theatre" or the executive control system of the mind.[10]

Inter-disciplinary perspectives

Western philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and how it fits into a larger picture of the world. These issues remain central to both continental and analytic philosophy, in phenomenology and the philosophy of mind, respectively. Some basic questions include: whether consciousness is the same kind of thing as matter; whether it may ever be possible for computing machines like computers or robots to be conscious; how consciousness relates to language; how consciousness as Being relates to the world of experience; the role of the self in experience; whether individual thought is possible at all; and whether the concept is fundamentally coherent.

Recently, consciousness has also become a significant topic of interdisciplinary research in cognitive science, involving fields such as psychology, linguistics, anthropology,[11] neuropsychology and neuroscience. The primary focus is on understanding what it means biologically and psychologically for information to be present in consciousness—that is, on determining the neural and psychological correlates of consciousness. The majority of experimental studies assess consciousness in humans by asking subjects for a verbal report of their experiences (e.g., "tell me if you notice anything when I do this"). Issues of interest include phenomena such as subliminal perception, blindsight, denial of impairment, and altered states of consciousness produced by alcohol and other drugs, or spiritual or meditative techniques.

In medicine, consciousness is assessed by observing a patient's arousal and responsiveness, and can be seen as a continuum of states ranging from full alertness and comprehension, through disorientation, delirium, loss of meaningful communication, and finally loss of movement in response to painful stimuli.[12] Issues of practical concern include how the presence of consciousness can be assessed in severely ill, comatose, or anesthetized people, and how to treat conditions in which consciousness is impaired or disrupted.[13] The degree of consciousness is measured by standardized behavior observation scales such as the Glasgow Coma Scale.

Etymology

John Locke, British Enlightenment philosopher active in the 17th century

The origin of the modern concept of consciousness is often attributed to John Locke's Essay Concerning Human Understanding, published in 1690.[14] Locke defined consciousness as "the perception of what passes in a man's own mind".[15] His essay influenced the 18th-century view of consciousness, and his definition appeared in Samuel Johnson's celebrated Dictionary (1755).[16] "Consciousness" (French: conscience) is also defined in the 1753 volume of Diderot and d'Alembert's Encyclopédie, as "the opinion or internal feeling that we ourselves have from what we do".[17]

The earliest English language uses of "conscious" and "consciousness" date back, however, to the 1500s. The English word "conscious" originally derived from the Latin conscius (con- "together" and scio "to know"), but the Latin word did not have the same meaning as our word—it meant "knowing with", in other words, "having joint or common knowledge with another".[18] There were, however, many occurrences in Latin writings of the phrase conscius sibi, which translates literally as "knowing with oneself", or in other words "sharing knowledge with oneself about something". This phrase had the figurative meaning of "knowing that one knows", as the modern English word "conscious" does. In its earliest uses in the 1500s, the English word "conscious" retained the meaning of the Latin conscius. For example, Thomas Hobbes in Leviathan wrote: "Where two, or more men, know of one and the same fact, they are said to be Conscious of it one to another."[19] The Latin phrase conscius sibi, whose meaning was more closely related to the current concept of consciousness, was rendered in English as "conscious to oneself" or "conscious unto oneself". For example, Archbishop Ussher wrote in 1613 of "being so conscious unto myself of my great weakness".[20] Locke's definition from 1690 illustrates that a gradual shift in meaning had taken place.

A related word was conscientia, which primarily means moral conscience. In the literal sense, "conscientia" means knowledge-with, that is, shared knowledge. The word first appears in Latin juridical texts by writers such as Cicero.[21] Here, conscientia is the knowledge that a witness has of the deed of someone else.[22] René Descartes (1596–1650) is generally taken to be the first philosopher to use conscientia in a way that does not fit this traditional meaning.[23] Descartes used conscientia the way modern speakers would use "conscience". In Search after Truth (Regulæ ad directionem ingenii ut et inquisitio veritatis per lumen naturale, Amsterdam 1701) he says "conscience or internal testimony" (conscientiâ, vel interno testimonio).[24][25]

Dictionary definitions

The dictionary meanings of the word consciousness extend through several centuries and several associated related meanings. These have ranged from formal definitions to definitions attempting to capture the less easily captured and more debated meanings and usage of the word.

One formal definition indicating the range of these related meanings is given in Webster's Third New International Dictionary stating that consciousness is:

    • awareness or perception of an inward psychological or spiritual fact: intuitively perceived knowledge of something in one's inner self
    • inward awareness of an external object, state, or fact
    • concerned awareness: INTEREST, CONCERN—often used with an attributive noun.
  1. the state or activity that is characterized by sensation, emotion, volition, or thought: mind in the broadest possible sense: something in nature that is distinguished from the physical.
  2. the totality in psychology of sensations, perceptions, ideas, attitudes, and feelings of which an individual or a group is aware at any given time or within a particular time span—compare STREAM OF CONSCIOUSNESS."

The Cambridge Dictionary defines consciousness as "the state of understanding and realizing something."[26] The Oxford Living Dictionary defines consciousness as "The state of being aware of and responsive to one's surroundings.", "A person's awareness or perception of something." and "The fact of awareness by the mind of itself and the world."[27]

Most definitions include awareness, but some include a more general state of being.

Philosophy of mind

The philosophy of mind has given rise to many stances regarding consciousness. The Routledge Encyclopedia of Philosophy in 1998 defines consciousness as follows:

Consciousness—Philosophers have used the term 'consciousness' for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience... Something within one's mind is 'introspectively conscious' just in case one introspects it (or is poised to do so). Introspection is often thought to deliver one's primary knowledge of one's mental life. An experience or other mental entity is 'phenomenally conscious' just in case there is 'something it is like' for one to have it. The clearest examples are: perceptual experience, such as tastings and seeings; bodily-sensational experiences, such as those of pains, tickles and itches; imaginative experiences, such as those of one's own actions or perceptions; and streams of thought, as in the experience of thinking 'in words' or 'in images'. Introspection and phenomenality seem independent, or dissociable, although this is controversial.[28]

In a more skeptical definition of consciousness, Stuart Sutherland has exemplified some of the difficulties in fully ascertaining all of its cognate meanings in his entry for the 1989 version of the Macmillan Dictionary of Psychology:

Consciousness—The having of perceptions, thoughts, and feelings; awareness. The term is impossible to define except in terms that are unintelligible without a grasp of what consciousness means. Many fall into the trap of equating consciousness with self-consciousness—to be conscious it is only necessary to be aware of the external world. Consciousness is a fascinating but elusive phenomenon: it is impossible to specify what it is, what it does, or why it has evolved. Nothing worth reading has been written on it.[29]

Most writers on the philosophy of consciousness have been concerned with defending a particular point of view, and have organized their material accordingly. For surveys, the most common approach is to follow a historical path by associating stances with the philosophers who are most strongly associated with them, for example, Descartes, Locke, Kant, etc. An alternative is to organize philosophical stances according to basic issues.

The coherence of the concept

Many philosophers have argued that consciousness is a unitary concept that is understood intuitively by the majority of people in spite of the difficulty in defining it.[8] Others, though, have argued that the level of disagreement about the meaning of the word indicates that it either means different things to different people (for instance, the objective versus subjective aspects of consciousness), or else it encompasses a variety of distinct meanings with no simple element in common.[30]

Philosophers differ from non-philosophers in their intuitions about what consciousness is.[31] While most people have a strong intuition for the existence of what they refer to as consciousness,[8] skeptics argue that this intuition is false, either because the concept of consciousness is intrinsically incoherent, or because our intuitions about it are based in illusions. Gilbert Ryle, for example, argued that traditional understanding of consciousness depends on a Cartesian dualist outlook that improperly distinguishes between mind and body, or between mind and world. He proposed that we speak not of minds, bodies, and the world, but of individuals, or persons, acting in the world. Thus, by speaking of "consciousness" we end up misleading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings.[32] More generally, many philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness.[29]

Types of consciousness

Ned Block proposed a distinction between two types of consciousness that he called phenomenal (P-consciousness) and access (A-consciousness).[33] P-consciousness, according to Block, is simply raw experience: it is moving, colored forms, sounds, sensations, emotions and feelings with our bodies and responses at the center. These experiences, considered independently of any impact on behavior, are called qualia. A-consciousness, on the other hand, is the phenomenon whereby information in our minds is accessible for verbal report, reasoning, and the control of behavior. So, when we perceive, information about what we perceive is access conscious; when we introspect, information about our thoughts is access conscious; when we remember, information about the past is access conscious, and so on. Although some philosophers, such as Daniel Dennett, have disputed the validity of this distinction,[34] others have broadly accepted it. David Chalmers has argued that A-consciousness can in principle be understood in mechanistic terms, but that understanding P-consciousness is much more challenging: he calls this the hard problem of consciousness.[35]. Kong Derick has also stated that there are two type of consciousness which are; high level consciousness which he attributes to the mind and low level consciousness which he attributes to the submind.[36]

Some philosophers believe that Block's two types of consciousness are not the end of the story. William Lycan, for example, argued in his book Consciousness and Experience that at least eight clearly distinct types of consciousness can be identified (organism consciousness; control consciousness; consciousness of; state/event consciousness; reportability; introspective consciousness; subjective consciousness; self-consciousness)—and that even this list omits several more obscure forms.[37]

There is also debate over whether or not A-consciousness and P-consciousness always coexist or if they can exist separately. Although P-consciousness without A-consciousness is more widely accepted, there have been some hypothetical examples of A without P. Block for instance suggests the case of a "zombie" that is computationally identical to a person but without any subjectivity. However, he remains somewhat skeptical concluding "I don't know whether there are any actual cases of A-consciousness without P-consciousness, but I hope I have illustrated their conceptual possibility." [38]

Mind–body problem

Main article: Mind–body problem

Illustration of dualism by René Descartes. Inputs are passed by the sensory organs to the pineal gland and from there to the immaterial spirit.

Mental processes (such as consciousness) and physical processes (such as brain events) seem to be correlated, however the specific nature of the connection is unknown.

The first influential philosopher to discuss this question specifically was Descartes, and the answer he gave is known as Cartesian dualism. Descartes proposed that consciousness resides within an immaterial domain he called res cogitans (the realm of thought), in contrast to the domain of material things, which he called res extensa (the realm of extension).[39] He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the pineal gland.[40]

Although it is widely accepted that Descartes explained the problem cogently, few later philosophers have been happy with his solution, and his ideas about the pineal gland have especially been ridiculed.[41] However, no alternative solution has gained general acceptance. Proposed solutions can be divided broadly into two categories: dualist solutions that maintain Descartes' rigid distinction between the realm of consciousness and the realm of matter but give different answers for how the two realms relate to each other; and monist solutions that maintain that there is really only one realm of being, of which consciousness and matter are both aspects. Each of these categories itself contains numerous variants. The two main types of dualism are substance dualism (which holds that the mind is formed of a distinct type of substance not governed by the laws of physics) and property dualism (which holds that the laws of physics are universally valid but cannot be used to explain the mind). The three main types of monism are physicalism (which holds that the mind consists of matter organized in a particular way), idealism (which holds that only thought or experience truly exists, and matter is merely an illusion), and neutral monism (which holds that both mind and matter are aspects of a distinct essence that is itself identical to neither of them). There are also, however, a large number of idiosyncratic theories that cannot cleanly be assigned to any of these schools of thought.[42]

Since the dawn of Newtonian science with its vision of simple mechanical principles governing the entire universe, some philosophers have been tempted by the idea that consciousness could be explained in purely physical terms. The first influential writer to propose such an idea explicitly was Julien Offray de La Mettrie, in his book Man a Machine (L'homme machine). His arguments, however, were very abstract.[43] The most influential modern physical theories of consciousness are based on psychology and neuroscience. Theories proposed by neuroscientists such as Gerald Edelman[44] and Antonio Damasio,[45] and by philosophers such as Daniel Dennett,[46] seek to explain consciousness in terms of neural events occurring within the brain. Many other neuroscientists, such as Christof Koch,[47] have explored the neural basis of consciousness without attempting to frame all-encompassing global theories. At the same time, computer scientists working in the field of artificial intelligence have pursued the goal of creating digital computer programs that can simulate or embody consciousness.[48]

A few theoretical physicists have argued that classical physics is intrinsically incapable of explaining the holistic aspects of consciousness, but that quantum theory may provide the missing ingredients. Several theorists have therefore proposed quantum mind (QM) theories of consciousness.[49] Notable theories falling into this category include the holonomic brain theory of Karl Pribram and David Bohm, and the Orch-OR theory formulated by Stuart Hameroff and Roger Penrose. Some of these QM theories offer descriptions of phenomenal consciousness, as well as QM interpretations of access consciousness. None of the quantum mechanical theories have been confirmed by experiment. Recent publications by G. Guerreshi, J. Cia, S. Popescu, and H. Briegel[50] could falsify proposals such as those of Hameroff, which rely on quantum entanglement in protein. At the present time many scientists and philosophers consider the arguments for an important role of quantum phenomena to be unconvincing.[51]

Apart from the general question of the "hard problem" of consciousness, roughly speaking, the question of how mental experience arises from a physical basis,[52] a more specialized question is how to square the subjective notion that we are in control of our decisions (at least in some small measure) with the customary view of causality that subsequent events are caused by prior events. The topic of free will is the philosophical and scientific examination of this conundrum.

Problem of other minds

Main article: Problem of other minds

Many philosophers consider experience to be the essence of consciousness, and believe that experience can only fully be known from the inside, subjectively. But if consciousness is subjective and not visible from the outside, why do the vast majority of people believe that other people are conscious, but rocks and trees are not?[53] This is called the problem of other minds.[54] It is particularly acute for people who believe in the possibility of philosophical zombies, that is, people who think it is possible in principle to have an entity that is physically indistinguishable from a human being and behaves like a human being in every way but nevertheless lacks consciousness.[55] Related issues have also been studied extensively by Greg Littmann of the University of Illinois,[56] and Colin Allen a professor at Indiana University regarding the literature and research studying artificial intelligence in androids.[57]

The most commonly given answer is that we attribute consciousness to other people because we see that they resemble us in appearance and behavior; we reason that if they look like us and act like us, they must be like us in other ways, including having experiences of the sort that we do.[58] There are, however, a variety of problems with that explanation. For one thing, it seems to violate the principle of parsimony, by postulating an invisible entity that is not necessary to explain what we observe.[58] Some philosophers, such as Daniel Dennett in an essay titled The Unimagined Preposterousness of Zombies, argue that people who give this explanation do not really understand what they are saying.[59] More broadly, philosophers who do not accept the possibility of zombies generally believe that consciousness is reflected in behavior (including verbal behavior), and that we attribute consciousness on the basis of behavior. A more straightforward way of saying this is that we attribute experiences to people because of what they can do, including the fact that they can tell us about their experiences.[60]

Animal consciousness

See also: Animal consciousness

The topic of animal consciousness is beset by a number of difficulties. It poses the problem of other minds in an especially severe form, because non-human animals, lacking the ability to express human language, cannot tell humans about their experiences.[61] Also, it is difficult to reason objectively about the question, because a denial that an animal is conscious is often taken to imply that it does not feel, its life has no value, and that harming it is not morally wrong. Descartes, for example, has sometimes been blamed for mistreatment of animals due to the fact that he believed only humans have a non-physical mind.[62] Most people have a strong intuition that some animals, such as cats and dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious, and are often based on personal interactions with pets and other animals they have observed.[61]

Philosophers who consider subjective experience the essence of consciousness also generally believe, as a correlate, that the existence and nature of animal consciousness can never rigorously be known. Thomas Nagel spelled out this point of view in an influential essay titled What Is it Like to Be a Bat?. He said that an organism is conscious "if and only if there is something that it is like to be that organism—something it is like for the organism"; and he argued that no matter how much we know about an animal's brain and behavior, we can never really put ourselves into the mind of the animal and experience its world in the way it does itself.[63] Other thinkers, such as Douglas Hofstadter, dismiss this argument as incoherent.[64] Several psychologists and ethologists have argued for the existence of animal consciousness by describing a range of behaviors that appear to show animals holding beliefs about things they cannot directly perceive—Donald Griffin's 2001 book Animal Minds reviews a substantial portion of the evidence.[65]

On July 7, 2012, eminent scientists from different branches of neuroscience gathered at the University of Cambridge to celebrate the Francis Crick Memorial Conference, which deals with consciousness in humans and pre-linguistic consciousness in nonhuman animals. After the conference, they signed in the presence of Stephen Hawking, the 'Cambridge Declaration on Consciousness', which summarizes the most important findings of the survey:

"We decided to reach a consensus and make a statement directed to the public that is not scientific. It's obvious to everyone in this room that animals have consciousness, but it is not obvious to the rest of the world. It is not obvious to the rest of the Western world or the Far East. It is not obvious to the society."[66]

"Convergent evidence indicates that non-human animals [...], including all mammals and birds, and other creatures, [...] have the necessary neural substrates of consciousness and the capacity to exhibit intentional behaviors."[67]

Artifact consciousness

See also: Artificial consciousness

The idea of an artifact made conscious is an ancient theme of mythology, appearing for example in the Greek myth of Pygmalion, who carved a statue that was magically brought to life, and in medieval Jewish stories of the Golem, a magically animated homunculus built of clay.[68] However, the possibility of actually constructing a conscious machine was probably first discussed by Ada Lovelace, in a set of notes written in 1842 about the Analytical Engine invented by Charles Babbage, a precursor (never built) to modern electronic computers. Lovelace was essentially dismissive of the idea that a machine such as the Analytical Engine could think in a humanlike way. She wrote:

It is desirable to guard against the possibility of exaggerated ideas that might arise as to the powers of the Analytical Engine. ... The Analytical Engine has no pretensions whatever to originate anything. It can do whatever we know how to order it to perform. It can follow analysis; but it has no power of anticipating any analytical relations or truths. Its province is to assist us in making available what we are already acquainted with.[69]

One of the most influential contributions to this question was an essay written in 1950 by pioneering computer scientist Alan Turing, titled Computing Machinery and Intelligence. Turing disavowed any interest in terminology, saying that even "Can machines think?" is too loaded with spurious connotations to be meaningful; but he proposed to replace all such questions with a specific operational test, which has become known as the Turing test.[70] To pass the test, a computer must be able to imitate a human well enough to fool interrogators. In his essay Turing discussed a variety of possible objections, and presented a counterargument to each of them. The Turing test is commonly cited in discussions of artificial intelligence as a proposed criterion for machine consciousness; it has provoked a great deal of philosophical debate. For example, Daniel Dennett and Douglas Hofstadter argue that anything capable of passing the Turing test is necessarily conscious,[71] while David Chalmers argues that a philosophical zombie could pass the test, yet fail to be conscious.[72] A third group of scholars have argued that with technological growth once machines begin to display any substantial signs of human-like behavior then the dichotomy (of human consciousness compared to human-like consciousness) becomes passé and issues of machine autonomy begin to prevail even as observed in its nascent form within contemporary industry and technology.[56][57] Jürgen Schmidhuber argues that consciousness is simply the result of compression.[73] As an agent sees representation of itself recurring in the environment, the compression of this representation can be called consciousness.

John Searle in December 2005

In a lively exchange over what has come to be referred to as "the Chinese room argument", John Searle sought to refute the claim of proponents of what he calls "strong artificial intelligence (AI)" that a computer program can be conscious, though he does agree with advocates of "weak AI" that computer programs can be formatted to "simulate" conscious states. His own view is that consciousness has subjective, first-person causal powers by being essentially intentional due simply to the way human brains function biologically; conscious persons can perform computations, but consciousness is not inherently computational the way computer programs are. To make a Turing machine that speaks Chinese, Searle imagines a room with one monolingual English speaker (Searle himself, in fact), a book that designates a combination of Chinese symbols to be output paired with Chinese symbol input, and boxes filled with Chinese symbols. In this case, the English speaker is acting as a computer and the rulebook as a program. Searle argues that with such a machine, he would be able to process the inputs to outputs perfectly without having any understanding of Chinese, nor having any idea what the questions and answers could possibly mean. If the experiment were done in English, since Searle knows English, he would be able to take questions and give answers without any algorithms for English questions, and he would be effectively aware of what was being said and the purposes it might serve. Searle would pass the Turing test of answering the questions in both languages, but he is only conscious of what he is doing when he speaks English. Another way of putting the argument is to say that computer programs can pass the Turing test for processing the syntax of a language, but that the syntax cannot lead to semantic meaning in the way strong AI advocates hoped.[74][75]

In the literature concerning artificial intelligence, Searle's essay has been second only to Turing's in the volume of debate it has generated.[76] Searle himself was vague about what extra ingredients it would take to make a machine conscious: all he proposed was that what was needed was "causal powers" of the sort that the brain has and that computers lack. But other thinkers sympathetic to his basic argument have suggested that the necessary (though perhaps still not sufficient) extra conditions may include the ability to pass not just the verbal version of the Turing test, but the robotic version,[77] which requires grounding the robot's words in the robot's sensorimotor capacity to categorize and interact with the things in the world that its words are about, Turing-indistinguishably from a real person. Turing-scale robotics is an empirical branch of research on embodied cognition and situated cognition.[78]

In 2014, Victor Argonov has suggested a non-Turing test for machine consciousness based on machine's ability to produce philosophical judgments.[79] He argues that a deterministic machine must be regarded as conscious if it is able to produce judgments on all problematic properties of consciousness (such as qualia or binding) having no innate (preloaded) philosophical knowledge on these issues, no philosophical discussions while learning, and no informational models of other creatures in its memory (such models may implicitly or explicitly contain knowledge about these creatures' consciousness). However, this test can be used only to detect, but not refute the existence of consciousness. A positive result proves that machine is conscious but a negative result proves nothing. For example, absence of philosophical judgments may be caused by lack of the machine's intellect, not by absence of consciousness.

Scientific study

For many decades, consciousness as a research topic was avoided by the majority of mainstream scientists, because of a general feeling that a phenomenon defined in subjective terms could not properly be studied using objective experimental methods.[80] In 1975 George Mandler published an influential psychological study which distinguished between slow, serial, and limited conscious processes and fast, parallel and extensive unconscious ones.[81] Starting in the 1980s, an expanding community of neuroscientists and psychologists have associated themselves with a field called Consciousness Studies, giving rise to a stream of experimental work published in books,[82] journals such as Consciousness and Cognition, Frontiers in Consciousness Research, Psyche, and the Journal of Consciousness Studies, along with regular conferences organized by groups such as the Association for the Scientific Study of Consciousness[83] and the Society for Consciousness Studies.

Modern medical and psychological investigations into consciousness are based on psychological experiments (including, for example, the investigation of priming effects using subliminal stimuli), and on case studies of alterations in consciousness produced by trauma, illness, or drugs. Broadly viewed, scientific approaches are based on two core concepts. The first identifies the content of consciousness with the experiences that are reported by human subjects; the second makes use of the concept of consciousness that has been developed by neurologists and other medical professionals who deal with patients whose behavior is impaired. In either case, the ultimate goals are to develop techniques for assessing consciousness objectively in humans as well as other animals, and to understand the neural and psychological mechanisms that underlie it.[47]

Measurement

The Necker cube, an ambiguous image

Experimental research on consciousness presents special difficulties, due to the lack of a universally accepted operational definition. In the majority of experiments that are specifically about consciousness, the subjects are human, and the criterion used is verbal report: in other words, subjects are asked to describe their experiences, and their descriptions are treated as observations of the contents of consciousness.[84] For example, subjects who stare continuously at a Necker cube usually report that they experience it "flipping" between two 3D configurations, even though the stimulus itself remains the same.[85] The objective is to understand the relationship between the conscious awareness of stimuli (as indicated by verbal report) and the effects the stimuli have on brain activity and behavior. In several paradigms, such as the technique of response priming, the behavior of subjects is clearly influenced by stimuli for which they report no awareness, and suitable experimental manipulations can lead to increasing priming effects despite decreasing prime identification (double dissociation).[86]

Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues.[87] For one thing, if verbal reports are treated as observations, akin to observations in other branches of science, then the possibility arises that they may contain errors—but it is difficult to make sense of the idea that subjects could be wrong about their own experiences, and even more difficult to see how such an error could be detected.[88] Daniel Dennett has argued for an approach he calls heterophenomenology, which means treating verbal reports as stories that may or may not be true, but his ideas about how to do this have not been widely adopted.[89] Another issue with verbal report as a criterion is that it restricts the field of study to humans who have language: this approach cannot be used to study consciousness in other species, pre-linguistic children, or people with types of brain damage that impair language. As a third issue, philosophers who dispute the validity of the Turing test may feel that it is possible, at least in principle, for verbal report to be dissociated from consciousness entirely: a philosophical zombie may give detailed verbal reports of awareness in the absence of any genuine awareness.[90]

Although verbal report is in practice the "gold standard" for ascribing consciousness, it is not the only possible criterion.[87] In medicine, consciousness is assessed as a combination of verbal behavior, arousal, brain activity and purposeful movement. The last three of these can be used as indicators of consciousness when verbal behavior is absent.[91] The scientific literature regarding the neural bases of arousal and purposeful movement is very extensive. Their reliability as indicators of consciousness is disputed, however, due to numerous studies showing that alert human subjects can be induced to behave purposefully in a variety of ways in spite of reporting a complete lack of awareness.[86] Studies of the neuroscience of free will have also shown that the experiences that people report when they behave purposefully sometimes do not correspond to their actual behaviors or to the patterns of electrical activity recorded from their brains.[92]

Another approach applies specifically to the study of self-awareness, that is, the ability to distinguish oneself from others. In the 1970s Gordon Gallup developed an operational test for self-awareness, known as the mirror test. The test examines whether animals are able to differentiate between seeing themselves in a mirror versus seeing other animals. The classic example involves placing a spot of coloring on the skin or fur near the individual's forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves.[93] Humans (older than 18 months) and other great apes, bottlenose dolphins, killer whales, pigeons, European magpies and elephants have all been observed to pass this test.[94]

Neural correlates

Schema of the neural processes underlying consciousness, from Christof Koch

A major part of the scientific literature on consciousness consists of studies that examine the relationship between the experiences reported by subjects and the activity that simultaneously takes place in their brains—that is, studies of the neural correlates of consciousness. The hope is to find that activity in a particular part of the brain, or a particular pattern of global brain activity, which will be strongly predictive of conscious awareness. Several brain imaging techniques, such as EEG and fMRI, have been used for physical measures of brain activity in these studies.[95]

Another idea that has drawn attention for several decades is that consciousness is associated with high-frequency (gamma band) oscillations in brain activity. This idea arose from proposals in the 1980s, by Christof von der Malsburg and Wolf Singer, that gamma oscillations could solve the so-called binding problem, by linking information represented in different parts of the brain into a unified experience.[96] Rodolfo Llinás, for example, proposed that consciousness results from recurrent thalamo-cortical resonance where the specific thalamocortical systems (content) and the non-specific (centromedial thalamus) thalamocortical systems (context) interact in the gamma band frequency via synchronous oscillations.[97]

A number of studies have shown that activity in primary sensory areas of the brain is not sufficient to produce consciousness: it is possible for subjects to report a lack of awareness even when areas such as the primary visual cortex show clear electrical responses to a stimulus.[98] Higher brain areas are seen as more promising, especially the prefrontal cortex, which is involved in a range of higher cognitive functions collectively known as executive functions. There is substantial evidence that a "top-down" flow of neural activity (i.e., activity propagating from the frontal cortex to sensory areas) is more predictive of conscious awareness than a "bottom-up" flow of activity.[99] The prefrontal cortex is not the only candidate area, however: studies by Nikos Logothetis and his colleagues have shown, for example, that visually responsive neurons in parts of the temporal lobe reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry).[100]

Modulation of neural responses may correlate with phenomenal experiences. In contrast to the raw electrical responses that do not correlate with consciousness, the modulation of these responses by other stimuli correlates surprisingly well with an important aspect of consciousness: namely with the phenomenal experience of stimulus intensity (brightness, contrast). In the research group of Danko Nikolić it has been shown that some of the changes in the subjectively perceived brightness correlated with the modulation of firing rates while others correlated with the modulation of neural synchrony.[101] An fMRI investigation suggested that these findings were strictly limited to the primary visual areas.[102] This indicates that, in the primary visual areas, changes in firing rates and synchrony can be considered as neural correlates of qualia—at least for some type of qualia.

In 2011, Graziano and Kastner[103] proposed the "attention schema" theory of awareness. In that theory, specific cortical areas, notably in the superior temporal sulcus and the temporo-parietal junction, are used to build the construct of awareness and attribute it to other people. The same cortical machinery is also used to attribute awareness to oneself. Damage to these cortical regions can lead to deficits in consciousness such as hemispatial neglect. In the attention schema theory, the value of explaining the feature of awareness and attributing it to a person is to gain a useful predictive model of that person's attentional processing. Attention is a style of information processing in which a brain focuses its resources on a limited set of interrelated signals. Awareness, in this theory, is a useful, simplified schema that represents attentional states. To be aware of X is explained by constructing a model of one's attentional focus on X.

In 2013, the perturbational complexity index (PCI) was proposed, a measure of the algorithmic complexity of the electrophysiological response of the cortex to transcranial magnetic stimulation. This measure was shown to be higher in individuals that are awake, in REM sleep or in a locked-in state than in those who are in deep sleep or in a vegetative state,[104] making it potentially useful as a quantitative assessment of consciousness states.

Assuming that not only humans but even some non-mammalian species are conscious, a number of evolutionary approaches to the problem of neural correlates of consciousness open up. For example, assuming that birds are conscious—a common assumption among neuroscientists and ethologists due to the extensive cognitive repertoire of birds—there are comparative neuroanatomical ways to validate some of the principal, currently competing, mammalian consciousness–brain theories. The rationale for such a comparative study is that the avian brain deviates structurally from the mammalian brain. So how similar are they? What homologues can be identified? The general conclusion from the study by Butler, et al.,[105] is that some of the major theories for the mammalian brain [106][107][108] also appear to be valid for the avian brain. The structures assumed to be critical for consciousness in mammalian brains have homologous counterparts in avian brains. Thus the main portions of the theories of Crick and Koch,[106] Edelman and Tononi,[107] and Cotterill [108] seem to be compatible with the assumption that birds are conscious. Edelman also differentiates between what he calls primary consciousness (which is a trait shared by humans and non-human animals) and higher-order consciousness as it appears in humans alone along with human language capacity.[107] Certain aspects of the three theories, however, seem less easy to apply to the hypothesis of avian consciousness. For instance, the suggestion by Crick and Koch that layer 5 neurons of the mammalian brain have a special role, seems difficult to apply to the avian brain, since the avian homologues have a different morphology. Likewise, the theory of Eccles[109][110] seems incompatible, since a structural homologue/analogue to the dendron has not been found in avian brains. The assumption of an avian consciousness also brings the reptilian brain into focus. The reason is the structural continuity between avian and reptilian brains, meaning that the phylogenetic origin of consciousness may be earlier than suggested by many leading neuroscientists.

Joaquin Fuster of UCLA has advocated the position of the importance of the prefrontal cortex in humans, along with the areas of Wernicke and Broca, as being of particular importance to the development of human language capacities neuro-anatomically necessary for the emergence of higher-order consciousness in humans.[111]

Biological function and evolution

Opinions are divided as to where in biological evolution consciousness emerged and about whether or not consciousness has any survival value. Some argue that consciousness is a byproduct of evolution. It has been argued that consciousness emerged (i) exclusively with the first humans, (ii) exclusively with the first mammals, (iii) independently in mammals and birds, or (iv) with the first reptiles.[112] Other authors date the origins of consciousness to the first animals with nervous systems or early vertebrates in the Cambrian over 500 million years ago.[113] Donald Griffin suggests in his book Animal Minds a gradual evolution of consciousness.[65] Each of these scenarios raises the question of the possible survival value of consciousness.

Thomas Henry Huxley defends in an essay titled On the Hypothesis that Animals are Automata, and its History an epiphenomenalist theory of consciousness according to which consciousness is a causally inert effect of neural activity—"as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery".[114] To this William James objects in his essay Are We Automata? by stating an evolutionary argument for mind-brain interaction implying that if the preservation and development of consciousness in the biological evolution is a result of natural selection, it is plausible that consciousness has not only been influenced by neural processes, but has had a survival value itself; and it could only have had this if it had been efficacious.[115][116] Karl Popper develops in the book The Self and Its Brain a similar evolutionary argument.[117]

Regarding the primary function of conscious processing, a recurring idea in recent theories is that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent.[118] This has been called the integration consensus. Another example has been proposed by Gerald Edelman called dynamic core hypothesis which puts emphasis on reentrant connections that reciprocally link areas of the brain in a massively parallel manner.[119] Edelman also stresses the importance of the evolutionary emergence of higher-order consciousness in humans from the historically older trait of primary consciousness which humans share with non-human animals (see Neural correlates section above). These theories of integrative function present solutions to two classic problems associated with consciousness: differentiation and unity. They show how our conscious experience can discriminate between a virtually unlimited number of different possible scenes and details (differentiation) because it integrates those details from our sensory systems, while the integrative nature of consciousness in this view easily explains how our experience can seem unified as one whole despite all of these individual parts. However, it remains unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Nor is it explained what specific causal role conscious integration plays, nor why the same functionality cannot be achieved without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds of information can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect.[120] Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see the article of E. Morsella.[120]

As noted earlier, even among writers who consider consciousness to be a well-defined thing, there is widespread dispute about which animals other than humans can be said to possess it.[121] Edelman has described this distinction as that of humans possessing higher-order consciousness while sharing the trait of primary consciousness with non-human animals (see previous paragraph). Thus, any examination of the evolution of consciousness is faced with great difficulties. Nevertheless, some writers have argued that consciousness can be viewed from the standpoint of evolutionary biology as an adaptation in the sense of a trait that increases fitness.[122] In his article "Evolution of consciousness", John Eccles argued that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness ("[a] psychon ... linked to [a] dendron through quantum physics").[123] Bernard Baars proposed that once in place, this "recursive" circuitry may have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms.[124] Peter Carruthers has put forth one such potential adaptive advantage gained by conscious creatures by suggesting that consciousness allows an individual to make distinctions between appearance and reality.[125] This ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (e.g. that water in the distance may be a mirage) and behave accordingly, and it could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends.

Other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes.[126][127] No one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. If evolutionary processes are blind to the difference between function F being performed by conscious organism O and non-conscious organism O*, it is unclear what adaptive advantage consciousness could provide.[128] As a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an exaptation arising as a consequence of other developments such as increases in brain size or cortical rearrangement.[113] Consciousness in this sense has been compared to the blind spot in the retina where it is not an adaption of the retina, but instead just a by-product of the way the retinal axons were wired.[129] Several scholars including Pinker, Chomsky, Edelman, and Luria have indicated the importance of the emergence of human language as an important regulative mechanism of learning and memory in the context of the development of higher-order consciousness (see Neural correlates section above).

States of consciousness

A Buddhist monk meditating

There are some brain states in which consciousness seems to be absent, including dreamless sleep, coma, and death. There are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. Some altered states occur naturally; others can be produced by drugs or brain damage.[130] Altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image and changes in meaning or significance.[131]

The two most widely accepted altered states are sleep and dreaming. Although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. During ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. During dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may however be interrupted by bizarre or fantastic intrusions.[132] Thought processes during the dream state frequently show a high level of irrationality. Both dream and non-dream states are associated with severe disruption of memory: it usually disappears in seconds during the non-dream state, and in minutes after awakening from a dream unless actively refreshed.[133]

Research conducted on the effects of partial epileptic seizures on consciousness found that patients who suffer from partial epileptic seizures experience altered states of consciousness.[134][135] In partial epileptic seizures, consciousness is impaired or lost while some aspects of consciousness, often automated behaviors, remain intact. Studies found that when measuring the qualitative features during partial epileptic seizures, patients exhibited an increase in arousal and became absorbed in the experience of the seizure, followed by difficulty in focusing and shifting attention.

A variety of psychoactive drugs, including alcohol, have notable effects on consciousness.[136] These range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, empathogens–entactogens such as MDMA ("Ecstasy"), or most notably by the class of drugs known as psychedelics.[130] LSD, mescaline, psilocybin, Dimethyltryptamine, and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality. The brain mechanisms underlying these effects are not as well understood as those induced by use of alcohol,[136] but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter serotonin play an essential role.[137]

There has been some research into physiological changes in yogis and people who practise various techniques of meditation. Some research with brain waves during meditation has reported differences between those corresponding to ordinary relaxation and those corresponding to meditation. It has been disputed, however, whether there is enough evidence to count these as physiologically distinct states of consciousness.[138]

The most extensive study of the characteristics of altered states of consciousness was made by psychologist Charles Tart in the 1960s and 1970s. Tart analyzed a state of consciousness as made up of a number of component processes, including exteroception (sensing the external world); interoception (sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment.[139] Each of these, in his view, could be altered in multiple ways by drugs or other manipulations. The components that Tart identified have not, however, been validated by empirical studies. Research in this area has not yet reached firm conclusions, but a recent questionnaire-based study identified eleven significant factors contributing to drug-induced states of consciousness: experience of unity; spiritual experience; blissful state; insightfulness; disembodiment; impaired control and cognition; anxiety; complex imagery; elementary imagery; audio-visual synesthesia; and changed meaning of percepts.[140]

Phenomenology

Phenomenology is a method of inquiry that attempts to examine the structure of consciousness in its own right, putting aside problems regarding the relationship of consciousness to the physical world. This approach was first proposed by the philosopher Edmund Husserl, and later elaborated by other philosophers and scientists.[141] Husserl's original concept gave rise to two distinct lines of inquiry, in philosophy and psychology. In philosophy, phenomenology has largely been devoted to fundamental metaphysical questions, such as the nature of intentionality ("aboutness"). In psychology, phenomenology largely has meant attempting to investigate consciousness using the method of introspection, which means looking into one's own mind and reporting what one observes. This method fell into disrepute in the early twentieth century because of grave doubts about its reliability, but has been rehabilitated to some degree, especially when used in combination with techniques for examining brain activity.[142]

Neon color spreading effect. The apparent bluish tinge of the white areas inside the circle is an illusion.

Square version of the neon spread illusion

Introspectively, the world of conscious experience seems to have considerable structure. Immanuel Kant asserted that the world as we perceive it is organized according to a set of fundamental "intuitions", which include 'object' (we perceive the world as a set of distinct things); 'shape'; 'quality' (color, warmth, etc.); 'space' (distance, direction, and location); and 'time'.[143] Some of these constructs, such as space and time, correspond to the way the world is structured by the laws of physics; for others the correspondence is not as clear. Understanding the physical basis of qualities, such as redness or pain, has been particularly challenging. David Chalmers has called this the hard problem of consciousness.[35] Some philosophers have argued that it is intrinsically unsolvable, because qualities ("qualia") are ineffable; that is, they are "raw feels", incapable of being analyzed into component processes.[144] Other psychologists and neuroscientists reject these arguments. For example, research on ideasthesia shows that qualia are organised into a semantic-like network. Nevertheless, it is clear that the relationship between a physical entity such as light and a perceptual quality such as color is extraordinarily complex and indirect, as demonstrated by a variety of optical illusions such as neon color spreading.[145]

In neuroscience, a great deal of effort has gone into investigating how the perceived world of conscious awareness is constructed inside the brain. The process is generally thought to involve two primary mechanisms: (1) hierarchical processing of sensory inputs, and (2) memory. Signals arising from sensory organs are transmitted to the brain and then processed in a series of stages, which extract multiple types of information from the raw input. In the visual system, for example, sensory signals from the eyes are transmitted to the thalamus and then to the primary visual cortex; inside the cerebral cortex they are sent to areas that extract features such as three-dimensional structure, shape, color, and motion.[146] Memory comes into play in at least two ways. First, it allows sensory information to be evaluated in the context of previous experience. Second, and even more importantly, working memory allows information to be integrated over time so that it can generate a stable representation of the world—Gerald Edelman expressed this point vividly by titling one of his books about consciousness The Remembered Present.[147] In computational neuroscience, Bayesian approaches to brain function have been used to understand both the evaluation of sensory information in light of previous experience, and the integration of information over time. Bayesian models of the brain are probabilistic inference models, in which the brain takes advantage of prior knowledge to interpret uncertain sensory inputs in order to formulate a conscious percept; Bayesian models have successfully predicted many perceptual phenomena in vision and the nonvisual senses.[148][149][150]

Despite the large amount of information available, many important aspects of perception remain mysterious. A great deal is known about low-level signal processing in sensory systems. However, how sensory systems, action systems, and language systems interact are poorly understood. At a deeper level, there are still basic conceptual issues that remain unresolved.[146] Many scientists have found it difficult to reconcile the fact that information is distributed across multiple brain areas with the apparent unity of consciousness: this is one aspect of the so-called binding problem.[151] There are also some scientists who have expressed grave reservations about the idea that the brain forms representations of the outside world at all: influential members of this group include psychologist J. J. Gibson and roboticist Rodney Brooks, who both argued in favor of "intelligence without representation".[152]

Entropic brain

The entropic brain is a theory of conscious states informed by neuroimaging research with psychedelic drugs. The theory suggests that the brain in primary states such as rapid eye movement (REM) sleep, early psychosis and under the influence of psychedelic drugs, is in a disordered state; normal waking consciousness constrains some of this freedom and makes possible metacognitive functions such as internal self-administered reality testing and self-awareness.[153][154][155][156] Criticism has included questioning whether the theory has been adequately tested.[157]

Medical aspects

The medical approach to consciousness is practically oriented. It derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs. In medicine, conceptual distinctions are considered useful to the degree that they can help to guide treatments. Whereas the philosophical approach to consciousness focuses on its fundamental nature and its contents, the medical approach focuses on the amount of consciousness a person has: in medicine, consciousness is assessed as a "level" ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end.[158]

Consciousness is of concern to patients and physicians, especially neurologists and anesthesiologists. Patients may suffer from disorders of consciousness, or may need to be anesthetized for a surgical procedure. Physicians may perform consciousness-related interventions such as instructing the patient to sleep, administering general anesthesia, or inducing medical coma.[158] Also, bioethicists may be concerned with the ethical implications of consciousness in medical cases of patients such as the Karen Ann Quinlan case,[159] while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works.[160]

Assessment

In medicine, consciousness is examined using a set of procedures known as neuropsychological assessment.[91] There are two commonly used methods for assessing the level of consciousness of a patient: a simple procedure that requires minimal training, and a more complex procedure that requires substantial expertise. The simple procedure begins by asking whether the patient is able to move and react to physical stimuli. If so, the next question is whether the patient can respond in a meaningful way to questions and commands. If so, the patient is asked for name, current location, and current day and time. A patient who can answer all of these questions is said to be "alert and oriented times four" (sometimes denoted "A&Ox4" on a medical chart), and is usually considered fully conscious.[161]

The more complex procedure is known as a neurological examination, and is usually carried out by a neurologist in a hospital setting. A formal neurological examination runs through a precisely delineated series of tests, beginning with tests for basic sensorimotor reflexes, and culminating with tests for sophisticated use of language. The outcome may be summarized using the Glasgow Coma Scale, which yields a number in the range 3–15, with a score of 3 to 8 indicating coma, and 15 indicating full consciousness. The Glasgow Coma Scale has three subscales, measuring the best motor response (ranging from "no motor response" to "obeys commands"), the best eye response (ranging from "no eye opening" to "eyes opening spontaneously") and the best verbal response (ranging from "no verbal response" to "fully oriented"). There is also a simpler pediatric version of the scale, for children too young to be able to use language.[158]

In 2013, an experimental procedure was developed to measure degrees of consciousness, the procedure involving stimulating the brain with a magnetic pulse, measuring resulting waves of electrical activity, and developing a consciousness score based on the complexity of the brain activity.[162]

Disorders of consciousness

Medical conditions that inhibit consciousness are considered disorders of consciousness.[163] This category generally includes minimally conscious state and persistent vegetative state, but sometimes also includes the less severe locked-in syndrome and more severe chronic coma.[163][164] Differential diagnosis of these disorders is an active area of biomedical research.[165][166][167] Finally, brain death results in an irreversible disruption of consciousness.[163] While other conditions may cause a moderate deterioration (e.g., dementia and delirium) or transient interruption (e.g., grand mal and petit mal seizures) of consciousness, they are not included in this category.

Disorder Description
Locked-in syndrome The patient has awareness, sleep-wake cycles, and meaningful behavior (viz., eye-movement), but is isolated due to quadriplegia and pseudobulbar palsy.
Minimally conscious state The patient has intermittent periods of awareness and wakefulness and displays some meaningful behavior.
Persistent vegetative state The patient has sleep-wake cycles, but lacks awareness and only displays reflexive and non-purposeful behavior.
Chronic coma The patient lacks awareness and sleep-wake cycles and only displays reflexive behavior.
Brain death The patient lacks awareness, sleep-wake cycles, and brain-mediated reflexive behavior.

Anosognosia

Main article: Anosognosia

One of the most striking disorders of consciousness goes by the name anosognosia, a Greek-derived term meaning 'unawareness of disease'. This is a condition in which patients are disabled in some way, most commonly as a result of a stroke, but either misunderstand the nature of the problem or deny that there is anything wrong with them.[168] The most frequently occurring form is seen in people who have experienced a stroke damaging the parietal lobe in the right hemisphere of the brain, giving rise to a syndrome known as hemispatial neglect, characterized by an inability to direct action or attention toward objects located to the left with respect to their bodies. Patients with hemispatial neglect are often paralyzed on the right side of the body, but sometimes deny being unable to move. When questioned about the obvious problem, the patient may avoid giving a direct answer, or may give an explanation that doesn't make sense. Patients with hemispatial neglect may also fail to recognize paralyzed parts of their bodies: one frequently mentioned case is of a man who repeatedly tried to throw his own paralyzed right leg out of the bed he was lying in, and when asked what he was doing, complained that somebody had put a dead leg into the bed with him. An even more striking type of anosognosia is Anton–Babinski syndrome, a rarely occurring condition in which patients become blind but claim to be able to see normally, and persist in this claim in spite of all evidence to the contrary.[169]

Stream of consciousness

Main article: Stream of consciousness (psychology)

William James is usually credited with popularizing the idea that human consciousness flows like a stream, in his Principles of Psychology of 1890. According to James, the "stream of thought" is governed by five characteristics: "(1) Every thought tends to be part of a personal consciousness. (2) Within each personal consciousness thought is always changing. (3) Within each personal consciousness thought is sensibly continuous. (4) It always appears to deal with objects independent of itself. (5) It is interested in some parts of these objects to the exclusion of others".[170] A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term Citta-saṃtāna, which is usually translated as mindstream or "mental continuum". Buddhist teachings describe that consciousness manifests moment to moment as sense impressions and mental phenomena that are continuously changing.[171] The teachings list six triggers that can result in the generation of different mental events.[171] These triggers are input from the five senses (seeing, hearing, smelling, tasting or touch sensations), or a thought (relating to the past, present or the future) that happen to arise in the mind. The mental events generated as a result of these triggers are: feelings, perceptions and intentions/behaviour. The moment-by-moment manifestation of the mind-stream is said to happen in every person all the time. It even happens in a scientist who analyses various phenomena in the world, or analyses the material body including the organ brain.[171] The manifestation of the mindstream is also described as being influenced by physical laws, biological laws, psychological laws, volitional laws, and universal laws.[171] The purpose of the Buddhist practice of mindfulness is to understand the inherent nature of the consciousness and its characteristics.[172]

Narrative form

In the west, the primary impact of the idea has been on literature rather than science: stream of consciousness as a narrative mode means writing in a way that attempts to portray the moment-to-moment thoughts and experiences of a character. This technique perhaps had its beginnings in the monologues of Shakespeare's plays, and reached its fullest development in the novels of James Joyce and Virginia Woolf, although it has also been used by many other noted writers.[173]

Here for example is a passage from Joyce's Ulysses about the thoughts of Molly Bloom:

Yes because he never did a thing like that before as ask to get his breakfast in bed with a couple of eggs since the City Arms hotel when he used to be pretending to be laid up with a sick voice doing his highness to make himself interesting for that old faggot Mrs Riordan that he thought he had a great leg of and she never left us a farthing all for masses for herself and her soul greatest miser ever was actually afraid to lay out 4d for her methylated spirit telling me all her ailments she had too much old chat in her about politics and earthquakes and the end of the world let us have a bit of fun first God help the world if all the women were her sort down on bathingsuits and lownecks of course nobody wanted her to wear them I suppose she was pious because no man would look at her twice I hope Ill never be like her a wonder she didnt want us to cover our faces but she was a welleducated woman certainly and her gabby talk about Mr Riordan here and Mr Riordan there I suppose he was glad to get shut of her.[174]

Spiritual approaches

Further information: Level of consciousness (esotericism) and Higher consciousness

To most philosophers, the word "consciousness" connotes the relationship between the mind and the world. To writers on spiritual or religious topics, it frequently connotes the relationship between the mind and God, or the relationship between the mind and deeper truths that are thought to be more fundamental than the physical world. The mystical psychiatrist Richard Maurice Bucke distinguished between three types of consciousness: 'Simple Consciousness', awareness of the body, possessed by many animals; 'Self Consciousness', awareness of being aware, possessed only by humans; and 'Cosmic Consciousness', awareness of the life and order of the universe, possessed only by humans who are enlightened.[175] Many more examples could be given, such as the various levels of spiritual consciousness presented by Prem Saran Satsangi and Stuart Hameroff.[176] The most thorough account of the spiritual approach may be Ken Wilber's book The Spectrum of Consciousness, a comparison of western and eastern ways of thinking about the mind. Wilber described consciousness as a spectrum with ordinary awareness at one end, and more profound types of awareness at higher levels.[177]

See also

References

  1. Ken Wilber (2002). The Spectrum of Consciousness. Motilal Banarsidass. pp. 3–16. ISBN 978-81-208-1848-4.

Further reading

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Consciousness


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http://onelook.com/?w=Consciousness&ls=a

an alert cognitive state in which you are aware of yourself and your situation ("He lost consciousness")


https://plato.stanford.edu/entries/consciousness/#PheStr

Consciousness

First published Fri Jun 18, 2004; substantive revision Tue Jan 14, 2014

Perhaps no aspect of mind is more familiar or more puzzling than consciousness and our conscious experience of self and world. The problem of consciousness is arguably the central issue in current theorizing about the mind. Despite the lack of any agreed upon theory of consciousness, there is a widespread, if less than universal, consensus that an adequate account of mind requires a clear understanding of it and its place in nature. We need to understand both what consciousness is and how it relates to other, nonconscious, aspects of reality.


1. History of the issue

Questions about the nature of conscious awareness have likely been asked for as long as there have been humans. Neolithic burial practices appear to express spiritual beliefs and provide early evidence for at least minimally reflective thought about the nature of human consciousness (Pearson 1999, Clark and Riel-Salvatore 2001). Preliterate cultures have similarly been found invariably to embrace some form of spiritual or at least animist view that indicates a degree of reflection about the nature of conscious awareness.

Nonetheless, some have argued that consciousness as we know it today is a relatively recent historical development that arose sometime after the Homeric era (Jaynes 1974). According to this view, earlier humans including those who fought the Trojan War did not experience themselves as unified internal subjects of their thoughts and actions, at least not in the ways we do today. Others have claimed that even during the classical period, there was no word of ancient Greek that corresponds to “consciousness” (Wilkes 1984, 1988, 1995). Though the ancients had much to say about mental matters, it is less clear whether they had any specific concepts or concerns for what we now think of as consciousness.

Although the words “conscious” and “conscience” are used quite differently today, it is likely that the Reformation emphasis on the latter as an inner source of truth played some role in the inward turn so characteristic of the modern reflective view of self. The Hamlet who walked the stage in 1600 already saw his world and self with profoundly modern eyes.

By the beginning of the early modern era in the seventeenth century, consciousness had come full center in thinking about the mind. Indeed from the mid-17th through the late 19th century, consciousness was widely regarded as essential or definitive of the mental. René Descartes defined the very notion of thought (pensée) in terms of reflexive consciousness or self-awareness. In the Principles of Philosophy (1640) he wrote,

By the word ‘thought’ (‘pensée’) I understand all that of which we are conscious as operating in us.

Later, toward the end of the 17th century, John Locke offered a similar if slightly more qualified claim in An Essay on Human Understanding (1688),

I do not say there is no soul in man because he is not sensible of it in his sleep. But I do say he can not think at any time, waking or sleeping, without being sensible of it. Our being sensible of it is not necessary to anything but our thoughts, and to them it is and to them it always will be necessary.

Locke explicitly forswore making any hypothesis about the substantial basis of consciousness and its relation to matter, but he clearly regarded it as essential to thought as well as to personal identity.

Locke's contemporary G.W. Leibniz, drawing possible inspiration from his mathematical work on differentiation and integration, offered a theory of mind in the Discourse on Metaphysics (1686) that allowed for infinitely many degrees of consciousness and perhaps even for some thoughts that were unconscious, the so called “petites perceptions”. Leibniz was the first to distinguish explicitly between perception and apperception, i.e., roughly between awareness and self-awareness. In the Monadology (1720) he also offered his famous analogy of the mill to express his belief that consciousness could not arise from mere matter. He asked his reader to imagine someone walking through an expanded brain as one would walk through a mill and observing all its mechanical operations, which for Leibniz exhausted its physical nature. Nowhere, he asserts, would such an observer see any conscious thoughts.

Despite Leibniz's recognition of the possibility of unconscious thought, for most of the next two centuries the domains of thought and consciousness were regarded as more or less the same. Associationist psychology, whether pursued by Locke or later in the eighteenth century by David Hume (1739) or in the nineteenth by James Mill (1829), aimed to discover the principles by which conscious thoughts or ideas interacted or affected each other. James Mill's son, John Stuart Mill continued his father's work on associationist psychology, but he allowed that combinations of ideas might produce resultants that went beyond their constituent mental parts, thus providing an early model of mental emergence (1865).

The purely associationist approach was critiqued in the late eighteenth century by Immanuel Kant (1787), who argued that an adequate account of experience and phenomenal consciousness required a far richer structure of mental and intentional organization. Phenomenal consciousness according to Kant could not be a mere succession of associated ideas, but at a minimum had to be the experience of a conscious self situated in an objective world structured with respect to space, time and causality.

Within the Anglo-American world, associationist approaches continued to be influential in both philosophy and psychology well into the twentieth century, while in the German and European sphere there was a greater interest in the larger structure of experience that lead in part to the study of phenomenology through the work of Edmund Husserl (1913, 1929), Martin Heidegger (1927), Maurice Merleau-Ponty (1945) and others who expanded the study of consciousness into the realm of the social, the bodily and the interpersonal.

At the outset of modern scientific psychology in the mid-nineteenth century, the mind was still largely equated with consciousness, and introspective methods dominated the field as in the work of Wilhelm Wundt (1897), Hermann von Helmholtz (1897), William James (1890) and Alfred Titchener (1901). However, the relation of consciousness to brain remained very much a mystery as expressed in T. H. Huxley's famous remark,

How it is that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp (1866).

The early twentieth century saw the eclipse of consciousness from scientific psychology, especially in the United States with the rise of behaviorism (Watson 1924, Skinner 1953) though movements such as Gestalt psychology kept it a matter of ongoing scientific concern in Europe (Köhler 1929, Köffka 1935). In the 1960s, the grip of behaviorism weakened with the rise of cognitive psychology and its emphasis on information processing and the modeling of internal mental processes (Neisser 1965, Gardiner 1985). However, despite the renewed emphasis on explaining cognitive capacities such as memory, perception and language comprehension, consciousness remained a largely neglected topic for several further decades.

In the 1980s and 90s there was a major resurgence of scientific and philosophical research into the nature and basis of consciousness (Baars 1988, Dennett 1991, Penrose 1989, 1994, Crick 1994, Lycan 1987, 1996, Chalmers 1996). Once consciousness was back under discussion, there was a rapid proliferation of research with a flood of books and articles, as well as the introduction of specialty journals (The Journal of Consciousness Studies, Consciousness and Cognition, Psyche), professional societies (Association for the Scientific Study of Consciousness—ASSC) and annual conferences devoted exclusively to its investigation (“The Science of Consciousness”).

2. Concepts of Consciousness

The words “conscious” and “consciousness” are umbrella terms that cover a wide variety of mental phenomena. Both are used with a diversity of meanings, and the adjective “conscious” is heterogeneous in its range, being applied both to whole organisms—creature consciousness—and to particular mental states and processes—state consciousness (Rosenthal 1986, Gennaro 1995, Carruthers 2000).

2.1 Creature Consciousness

An animal, person or other cognitive system may be regarded as conscious in a number of different senses.

Sentience. It may be conscious in the generic sense of simply being a sentient creature, one capable of sensing and responding to its world (Armstrong 1981). Being conscious in this sense may admit of degrees, and just what sort of sensory capacities are sufficient may not be sharply defined. Are fish conscious in the relevant respect? And what of shrimp or bees?

Wakefulness. One might further require that the organism actually be exercising such a capacity rather than merely having the ability or disposition to do so. Thus one might count it as conscious only if it were awake and normally alert. In that sense organisms would not count as conscious when asleep or in any of the deeper levels of coma. Again boundaries may be blurry, and intermediate cases may be involved. For example, is one conscious in the relevant sense when dreaming, hypnotized or in a fugue state?

Self-consciousness. A third and yet more demanding sense might define conscious creatures as those that are not only aware but also aware that they are aware, thus treating creature consciousness as a form of self-consciousness (Carruthers 2000). The self-awareness requirement might get interpreted in a variety of ways, and which creatures would qualify as conscious in the relevant sense will vary accordingly. If it is taken to involve explicit conceptual self-awareness, many non-human animals and even young children might fail to qualify, but if only more rudimentary implicit forms of self-awareness are required then a wide range of nonlinguistic creatures might count as self-conscious.

What it is like. Thomas Nagel's (1974) famous“what it is like” criterion aims to capture another and perhaps more subjective notion of being a conscious organism. According to Nagel, a being is conscious just if there is “something that it is like” to be that creature, i.e., some subjective way the world seems or appears from the creature's mental or experiential point of view. In Nagel's example, bats are conscious because there is something that it is like for a bat to experience its world through its echo-locatory senses, even though we humans from our human point of view can not emphatically understand what such a mode of consciousness is like from the bat's own point of view.

Subject of conscious states. A fifth alternative would be to define the notion of a conscious organism in terms of conscious states. That is, one might first define what makes a mental state a conscious mental state, and then define being a conscious creature in terms of having such states. One's concept of a conscious organism would then depend upon the particular account one gives of conscious states (section 2.2).

Transitive Consciousness. In addition to describing creatures as conscious in these various senses, there are also related senses in which creatures are described as being conscious of various things. The distinction is sometimes marked as that between transitive and intransitive notions of consciousness, with the former involving some object at which consciousness is directed (Rosenthal 1986).

2.2 State consciousness

The notion of a conscious mental state also has a variety of distinct though perhaps interrelated meanings. There are at least six major options.

States one is aware of. On one common reading, a conscious mental state is simply a mental state one is aware of being in (Rosenthal 1986, 1996). Conscious states in this sense involve a form of meta-mentality or meta-intentionality in so far as they require mental states that are themselves about mental states. To have a conscious desire for a cup of coffee is to have such a desire and also to be simultaneously and directly aware that one has such a desire. Unconscious thoughts and desires in this sense are simply those we have without being aware of having them, whether our lack of self-knowledge results from simple inattention or more deeply psychoanalytic causes.

Qualitative states. States might also be regarded as conscious in a seemingly quite different and more qualitative sense. That is, one might count a state as conscious just if it has or involves qualitative or experiential properties of the sort often referred to as “qualia” or “raw sensory feels”. (See the entry on qualia.) One's perception of the Merlot one is drinking or of the fabric one is examining counts as a conscious mental state in this sense because it involves various sensory qualia, e.g., taste qualia in the wine case and color qualia in one's visual experience of the cloth. There is considerable disagreement about the nature of such qualia (Churchland 1985, Shoemaker 1990, Clark 1993, Chalmers 1996) and even about their existence. Traditionally qualia have been regarded as intrinsic, private, ineffable monadic features of experience, but current theories of qualia often reject at least some of those commitments (Dennett 1990).

Phenomenal states. Such qualia are sometimes referred to as phenomenal properties and the associated sort of consciousness as phenomenal consciousness, but the latter term is perhaps more properly applied to the overall structure of experience and involves far more than sensory qualia. The phenomenal structure of consciousness also encompasses much of the spatial, temporal and conceptual organization of our experience of the world and of ourselves as agents in it. (See section 4.3) It is therefore probably best, at least initially, to distinguish the concept of phenomenal consciousness from that of qualitative consciousness, though they no doubt overlap.

What-it-is-like states. Consciousness in both those senses links up as well with Thomas Nagel's (1974) notion of a conscious creature, insofar as one might count a mental state as conscious in the “what it is like” sense just if there is something that it is like to be in that state. Nagel's criterion might be understood as aiming to provide a first-person or internal conception of what makes a state a phenomenal or qualitative state.

Access consciousness. States might be conscious in a seemingly quite different access sense, which has more to do with intra-mental relations. In this respect, a state's being conscious is a matter of its availability to interact with other states and of the access that one has to its content. In this more functional sense, which corresponds to what Ned Block (1995) calls access consciousness, a visual state's being conscious is not so much a matter of whether or not it has a qualitative “what it's likeness”, but of whether or not it and the visual information that it carries is generally available for use and guidance by the organism. In so far as the information in that state is richly and flexibly available to its containing organism, then it counts as a conscious state in the relevant respect, whether or not it has any qualitative or phenomenal feel in the Nagel sense.

Narrative consciousness. States might also be regarded as conscious in a narrative sense that appeals to the notion of the “stream of consciousness”, regarded as an ongoing more or less serial narrative of episodes from the perspective of an actual or merely virtual self. The idea would be to equate the person's conscious mental states with those that appear in the stream (Dennett 1991, 1992).

Although these six notions of what makes a state conscious can be independently specified, they are obviously not without potential links, nor do they exhaust the realm of possible options. Drawing connections, one might argue that states appear in the stream of consciousness only in so far as we are aware of them, and thus forge a bond between the first meta-mental notion of a conscious state and the stream or narrative concept. Or one might connect the access with the qualitative or phenomenal notions of a conscious state by trying to show that states that represent in those ways make their contents widely available in the respect required by the access notion.

Aiming to go beyond the six options, one might distinguish conscious from nonconscious states by appeal to aspects of their intra-mental dynamics and interactions other than mere access relations; e.g., conscious states might manifest a richer stock of content-sensitive interactions or a greater degree of flexible purposive guidance of the sort associated with the self-conscious control of thought. Alternatively, one might try to define conscious states in terms of conscious creatures. That is, one might give some account of what it is to be a conscious creature or perhaps even a conscious self, and then define one's notion of a conscious state in terms of being a state of such a creature or system, which would be the converse of the last option considered above for defining conscious creatures in terms of conscious mental states.

2.3 Consciousness as an entity

The noun “consciousness” has an equally diverse range of meanings that largely parallel those of the adjective “conscious”. Distinctions can be drawn between creature and state consciousness as well as among the varieties of each. One can refer specifically to phenomenal consciousness, access consciousness, reflexive or meta-mental consciousness, and narrative consciousness among other varieties.

Here consciousness itself is not typically treated as a substantive entity but merely the abstract reification of whatever property or aspect is attributed by the relevant use of the adjective “conscious”. Access consciousness is just the property of having the required sort of internal access relations, and qualitative consciousness is simply the property that is attributed when “conscious” is applied in the qualitative sense to mental states. How much this commits one to the ontological status of consciousness per se will depend on how much of a Platonist one is about universals in general. (See the entry on the medieval problem of universals.) It need not commit one to consciousness as a distinct entity any more than one's use of “square”, “red” or “gentle” commits one to the existence of squareness, redness or gentleness as distinct entities.

Though it is not the norm, one could nonetheless take a more robustly realist view of consciousness as a component of reality. That is one could think of consciousness as more on a par with electromagnetic fields than with life.

Since the demise of vitalism, we do not think of life per se as something distinct from living things. There are living things including organisms, states, properties and parts of organisms, communities and evolutionary lineages of organisms, but life is not itself a further thing, an additional component of reality, some vital force that gets added into living things. We apply the adjectives “living” and “alive” correctly to many things, and in doing so we might be said to be attributing life to them but with no meaning or reality other than that involved in their being living things.

Electromagnetic fields by contrast are regarded as real and independent parts of our physical world. Even though one may sometimes be able to specify the values of such a field by appeal to the behavior of particles in it, the fields themselves are regarded as concrete constituents of reality and not merely as abstractions or sets of relations among particles.

Similarly one could regard “consciousness” as referring to a component or aspect of reality that manifests itself in conscious states and creatures but is more than merely the abstract nominalization of the adjective “conscious” we apply to them. Though such strongly realist views are not very common at present, they should be included within the logical space of options.

There are thus many concepts of consciousness, and both “conscious” and “consciousness” are used in a wide range of ways with no privileged or canonical meaning. However, this may be less of an embarrassment than an embarrassment of riches. Consciousness is a complex feature of the world, and understanding it will require a diversity of conceptual tools for dealing with its many differing aspects. Conceptual plurality is thus just what one would hope for. As long as one avoids confusion by being clear about one's meanings, there is great value in having a variety of concepts by which we can access and grasp consciousness in all its rich complexity. However, one should not assume that conceptual plurality implies referential divergence. Our multiple concepts of consciousness may in fact pick out varying aspects of a single unified underlying mental phenomenon. Whether and to what extent they do so remains an open question.

3. Problems of Consciousness

The task of understanding consciousness is an equally diverse project. Not only do many different aspects of mind count as conscious in some sense, each is also open to various respects in which it might be explained or modeled. Understanding consciousness involves a multiplicity not only of explananda but also of questions that they pose and the sorts of answers they require. At the risk of oversimplifying, the relevant questions can be gathered under three crude rubrics as the What, How, and Why questions:

  • The Descriptive Question: What is consciousness? What are its principal features? And by what means can they be best discovered, described and modeled?
  • The Explanatory Question: How does consciousness of the relevant sort come to exist? Is it a primitive aspect of reality, and if not how does (or could) consciousness in the relevant respect arise from or be caused by nonconscious entities or processes?
  • The Functional Question: Why does consciousness of the relevant sort exist? Does it have a function, and if so what is it? Does it act causally and if so with what sorts of effects? Does it make a difference to the operation of systems in which it is present, and if so why and how?

The three questions focus respectively on describing the features of consciousness, explaining its underlying basis or cause, and explicating its role or value. The divisions among the three are of course somewhat artificial, and in practice the answers one gives to each will depend in part on what one says about the others. One can not, for example, adequately answer the what question and describe the main features of consciousness without addressing the why issue of its functional role within systems whose operations it affects. Nor could one explain how the relevant sort of consciousness might arise from nonconscious processes unless one had a clear account of just what features had to be caused or realized to count as producing it. Those caveats notwithstanding, the three-way division of questions provides a useful structure for articulating the overall explanatory project and for assessing the adequacy of particular theories or models of consciousness.

4. The descriptive question: What are the features of consciousness?

The What question asks us to describe and model the principal features of consciousness, but just which features are relevant will vary with the sort of consciousness we aim to capture. The main properties of access consciousness may be quite unlike those of qualitative or phenomenal consciousness, and those of reflexive consciousness or narrative consciousness may differ from both. However, by building up detailed theories of each type, we may hope to find important links between them and perhaps even to discover that they coincide in at least some key respects.

4.1 First-person and third-person data

The general descriptive project will require a variety of investigational methods (Flanagan 1992). Though one might naively regard the facts of consciousness as too self-evident to require any systematic methods of gathering data, the epistemic task is in reality far from trivial (Husserl 1913).

First-person introspective access provides a rich and essential source of insight into our conscious mental life, but it is neither sufficient in itself nor even especially helpful unless used in a trained and disciplined way. Gathering the needed evidence about the structure of experience requires us both to become phenomenologically sophisticated self-observers and to complement our introspective results with many types of third-person data available to external observers (Searle 1992, Varela 1995, Siewert 1998)

As phenomenologists have known for more than a century, discovering the structure of conscious experience demands a rigorous inner-directed stance that is quite unlike our everyday form of self-awareness (Husserl 1929, Merleau-Ponty 1945). Skilled observation of the needed sort requires training, effort and the ability to adopt alternative perspectives on one's experience.

The need for third-person empirical data gathered by external observers is perhaps most obvious with regard to the more clearly functional types of consciousness such as access consciousness, but it is required even with regard to phenomenal and qualitative consciousness. For example, deficit studies that correlate various neural and functional sites of damage with abnormalities of conscious experience can make us aware of aspects of phenomenal structure that escape our normal introspective awareness. As such case studies show, things can come apart in experience that seem inseparably unified or singular from our normal first-person point of view (Sacks 1985, Shallice 1988, Farah 1995).

Or to pick another example, third-person data can make us aware of how our experiences of acting and our experiences of event-timing affect each other in ways that we could never discern through mere introspection (Libet 1985, Wegner 2002). Nor are the facts gathered by these third person methods merely about the causes or bases of consciousness; they often concern the very structure of phenomenal consciousness itself. First-person, third-person and perhaps even second-person (Varela 1995) interactive methods will all be needed to collect the requisite evidence.

Using all these sources of data, we will hopefully be able to construct detailed descriptive models of the various sorts of consciousness. Though the specific features of most importance may vary among the different types, our overall descriptive project will need to address at least the following seven general aspects of consciousness (sections 4.2–4.7).

4.2 Qualitative character

Qualitative character is often equated with so called “raw feels” and illustrated by the redness one experiences when one looks at ripe tomatoes or the specific sweet savor one encounters when one tastes an equally ripe pineapple (Locke 1688). The relevant sort of qualitative character is not restricted to sensory states, but is typically taken to be present as an aspect of experiential states in general, such as experienced thoughts or desires (Siewert 1998).

The existence of such feels may seem to some to mark the threshold for states or creatures that are really conscious. If an organism senses and responds in apt ways to its world but lacks such qualia, then it might count as conscious at best in a loose and less than literal sense. Or so at least it would seem to those who take qualitative consciousness in the “what it is like” sense to be philosophically and scientifically central (Nagel 1974, Chalmers 1996).

Qualia problems in many forms—Can there be inverted qualia? (Block 1980a 1980b, Shoemaker 1981, 1982) Are qualia epiphenomenal? (Jackson 1982, Chalmers 1996) How could neural states give rise to qualia? (Levine 1983, McGinn 1991)—have loomed large in the recent past. But the What question raises a more basic problem of qualia: namely that of giving a clear and articulated description of our qualia space and the status of specific qualia within it.

Absent such a model, factual or descriptive errors are all too likely. For example, claims about the unintelligibility of the link between experienced red and any possible neural substrate of such an experience sometimes treat the relevant color quale as a simple and sui generis property (Levine 1983), but phenomenal redness in fact exists within a complex color space with multiple systematic dimensions and similarity relations (Hardin 1992). Understanding the specific color quale relative to that larger relational structure not only gives us a better descriptive grasp of its qualitative nature, it may also provide some “hooks” to which one might attach intelligible psycho-physical links.

Color may be the exception in terms of our having a specific and well developed formal understanding of the relevant qualitative space, but it is not likely an exception with regard to the importance of such spaces to our understanding of qualitative properties in general (Clark 1993, P.M. Churchland 1995). (See the entry on qualia.)

4.3 Phenomenal structure

Phenomenal structure should not be conflated with qualitative structure, despite the sometimes interchangeable use of “qualia” and “phenomenal properties” in the literature. “Phenomenal organization” covers all the various kinds of order and structure found within the domain of experience, i.e., within the domain of the world as it appears to us. There are obviously important links between the phenomenal and the qualitative. Indeed qualia might be best understood as properties of phenomenal or experienced objects, but there is in fact far more to the phenomenal than raw feels. As Kant (1787), Husserl (1913), and generations of phenomenologists have shown, the phenomenal structure of experience is richly intentional and involves not only sensory ideas and qualities but complex representations of time, space, cause, body, self, world and the organized structure of lived reality in all its conceptual and nonconceptual forms.

Since many non-conscious states also have intentional and representational aspects, it may be best to consider phenomenal structure as involving a special kind of intentional and representational organization and content, the kind distinctively associated with consciousness (Siewert 1998). (See the entry on representational theories of consciousness).

Answering the What question requires a careful account of the coherent and densely organized representational framework within which particular experiences are embedded. Since most of that structure is only implicit in the organization of experience, it can not just be read off by introspection. Articulating the structure of the phenomenal domain in a clear and intelligible way is a long and difficult process of inference and model building (Husserl 1929). Introspection can aid it, but a lot of theory construction and ingenuity are also needed.

There has been recent philosophical debate about the range of properties that are phenomenally present or manifest in conscious experience, in particular with respect to cognitive states such as believing or thinking. Some have argued for a so called “thin” view according to which phenomenal properties are limited to qualia representing basic sensory properties, such as colors, shapes, tones and feels. According to such theorists, there is no distinctive “what-it-is-likeness” involved in believing that Paris is the capital of France or that 17 is a prime number (Tye, Prinz 2012). Some imagery, e.g., of the Eiffel Tower, may accompany our having such a thought, but that is incidental to it and the cognitive state itself has no phenomenal feel. On the thin view, the phenomenal aspect of perceptual states as well is limited to basic sensory features; when one sees an image of Winston Churchill, one's perceptual phenomenology is limited only to the spatial aspects of his face.

Others holds a “thick” view according to which the phenomenology of perception includes a much wider range of features and cognitive states have a distinctive phenomenology as well (Strawson 2003, Pitt 2004, Seigel 2010). On the thick view, the what-it-is-likeness of perceiving an image of Marilyn Monroe includes one's recognition of her history as part of the felt aspect of the experience, and beliefs and thoughts as well can and typically do have a distinctive nonsensory phenomenology. Both sides of the debate are well represented in the volume Cognitive Phenomenology (Bayne and Montague 2010).

4.4 Subjectivity

Subjectivity is another notion sometimes equated with the qualitative or the phenomenal aspects of consciousness in the literature, but again there are good reason to recognize it, at least in some of its forms, as a distinct feature of consciousness—related to the qualitative and the phenomenal but different from each. In particular, the epistemic form of subjectivity concerns apparent limits on the knowability or even the understandability of various facts about conscious experience (Nagel 1974, Van Gulick 1985, Lycan 1996).

On Thomas Nagel's (1974) account, facts about what it is like to be a bat are subjective in the relevant sense because they can be fully understood only from the bat-type point of view. Only creatures capable of having or undergoing similar such experiences can understand their what-it's-likeness in the requisite empathetic sense. Facts about conscious experience can be at best incompletely understood from an outside third person point of view, such as those associated with objective physical science. A similar view about the limits of third-person theory seems to lie behind claims regarding what Frank Jackson's (1982) hypothetical Mary, the super color scientist, could not understand about experiencing red because of her own impoverished history of achromatic visual experience.

Whether facts about experience are indeed epistemically limited in this way is open to debate (Lycan 1996), but the claim that understanding consciousness requires special forms of knowing and access from the inside point of view is intuitively plausible and has a long history (Locke 1688). Thus any adequate answer to the What question must address the epistemic status of consciousness, both our abilities to understand it and their limits (Papineau 2002, Chalmers 2003). (See the entry on self-knowledge).

4.5 Self-perspectival organization

The perspectival structure of consciousness is one aspect of its overall phenomenal organization, but it is important enough to merit discussion in its own right. Insofar as the key perspective is that of the conscious self, the specific feature might be called self-perspectuality. Conscious experiences do not exist as isolated mental atoms, but as modes or states of a conscious self or subject (Descartes 1644, Searle 1992, though pace Hume 1739). A visual experience of a blue sphere is always a matter of there being some self or subject who is appeared to in that way. A sharp and stabbing pain is always a pain felt or experienced by some conscious subject. The self need not appear as an explicit element in our experiences, but as Kant (1787) noted the “I think” must at least potentially accompany each of them.

The self might be taken as the perspectival point from which the world of objects is present to experience (Wittgenstein 1921). It provides not only a spatial and temporal perspective for our experience of the world but one of meaning and intelligibility as well. The intentional coherence of the experiential domain relies upon the dual interdependence between self and world: the self as perspective from which objects are known and the world as the integrated structure of objects and events whose possibilities of being experienced implicitly define the nature and location of the self (Kant 1787, Husserl 1929).

Conscious organisms obviously differ in the extent to which they constitute a unified and coherent self, and they likely differ accordingly in the sort or degree of perspectival focus they embody in their respective forms of experience (Lorenz 1977). Consciousness may not require a distinct or substantial self of the traditional Cartesian sort, but at least some degree of perspectivally self-like organization seems essential for the existence of anything that might count as conscious experience. Experiences seem no more able to exist without a self or subject to undergo them than could ocean waves exist without the sea through which they move. The Descriptive question thus requires some account of the self-perspectival aspect of experience and the self-like organization of conscious minds on which it depends, even if the relevant account treats the self in a relatively deflationary and virtual way (Dennett 1991, 1992).

4.6 Unity

Unity is closely linked with the self-perspective, but it merits specific mention on its own as a key aspect of the organization of consciousness. Conscious systems and conscious mental states both involve many diverse forms of unity. Some are causal unities associated with the integration of action and control into a unified focus of agency. Others are more representational and intentional forms of unity involving the integration of diverse items of content at many scales and levels of binding (Cleeremans 2003).

Some such integrations are relatively local as when diverse features detected within a single sense modality are combined into a representation of external objects bearing those features, e.g. when one has a conscious visual experience of a moving red soup can passing above a green striped napkin (Triesman and Gelade 1980).

Other forms of intentional unity encompass a far wider range of contents. The content of one's present experience of the room in which one sits depends in part upon its location within a far larger structure associated with one's awareness of one's existence as an ongoing temporally extended observer within a world of spatially connected independently existing objects (Kant 1787, Husserl 1913). The individual experience can have the content that it does only because it resides within that larger unified structure of representation. (See the entry on unity of consciousness.)

Particular attention has been paid recently to the notion of phenomenal unity (Bayne 2010) and its relation to other forms of conscious unity such as those involving representational, functional or neural integration. Some have argued that phenomenal unity can be reduced to representational unity (Tye 2005) while others have denied the possibility of any such reduction (Bayne 2010).

4.7 Intentionality and transparency

Conscious mental states are typically regarded as having a representational or intentional aspect in so far as they are about things, refer to things or have satisfaction conditions. One's conscious visual experience correctly represents the world if there are lilacs in a white vase on the table (pace Travis 2004), one's conscious memory is of the attack on the World Trade Center, and one's conscious desire is for a glass of cold water. However, nonconscious states can also exhibit intentionality in such ways, and it is important to understand the ways in which the representational aspects of conscious states resemble and differ from those of nonconscious states (Carruthers 2000). Searle (1990) offers a contrary view according to which only conscious states and dispositions to have conscious states can be genuinely intentional, but most theorists regard intentionality as extending widely into the unconscious domain. (See the entry on consciousness and intentionality.)

One potentially important dimension of difference concerns so called transparency, which is an important feature of consciousness in two interrelated metaphoric senses, each of which has an intentional, an experiential and a functional aspect.

Conscious perceptual experience is often said to be transparent, or in G.E. Moore's (1922) phrase “diaphanous”. We transparently “look through” our sensory experience in so far as we seem directly aware of external objects and events present to us rather than being aware of any properties of experience by which it presents or represents such objects to us. When I look out at the wind-blown meadow, it is the undulating green grass of which I am aware not of any green property of my visual experience. (See the entry on representational theories of consciousness.) Moore himself believed we could become aware of those latter qualities with effort and redirection of attention, though some contemporary transparency advocates deny it (Harman 1990, Tye 1995, Kind 2003).

Conscious thoughts and experiences are also transparent in a semantic sense in that their meanings seem immediately known to us in the very act of thinking them (Van Gulick 1992). In that sense we might be said to ‘think right through’ them to what they mean or represent. Transparency in this semantic sense may correspond at least partly with what John Searle calls the “intrinsic intentionality” of consciousness (Searle 1992).

Our conscious mental states seem to have their meanings intrinsically or from the inside just by being what they are in themselves, by contrast with many externalist theories of mental content that ground meaning in causal, counterfactual or informational relations between bearers of intentionality and their semantic or referential objects.

The view of conscious content as intrinsically determined and internally self-evident is sometimes supported by appeals to brain in the vat intuitions, which make it seem that the envatted brain's conscious mental states would keep all their normal intentional contents despite the loss of all their normal causal and informational links to the world (Horgan and Tienson 2002). There is continued controversy about such cases and about competing internalist (Searle 1992) and externalist views (Dretske 1995) of conscious intentionality.

Though semantic transparency and intrinsic intentionality have some affinities, they should not be simply equated, since it may be possible to accommodate the former notion within a more externalist account of content and meaning. Both semantic and sensory transparency obviously concern the representational or intentional aspects of consciousness, but they are also experiential aspects of our conscious life. They are part of what it's like or how it feels phenomenally to be conscious. They also both have functional aspects, in so far as conscious experiences interact with each other in richly content-appropriate ways that manifest our transparent understanding of their contents.

4.8 Dynamic flow

The dynamics of consciousness are evident in the coherent order of its ever changing process of flow and self-transformation, what William James (1890) called the “stream of consciousness.” Some temporal sequences of experience are generated by purely internal factors as when one thinks through a puzzle, and others depend in part upon external causes as when one chases a fly ball, but even the latter sequences are shaped in large part by how consciousness transforms itself.

Whether partly in response to outer influences or entirely from within, each moment to moment sequence of experience grows coherently out of those that preceded it, constrained and enabled by the global structure of links and limits embodied in its underlying prior organization (Husserl 1913). In that respect, consciousness is an autopoietic system, i.e., a self-creating and self-organizing system (Varela and Maturana 1980).

As a conscious mental agent I can do many things such as scan my room, scan a mental image of it, review in memory the courses of a recent restaurant meal along with many of its tastes and scents, reason my way through a complex problem, or plan a grocery shopping trip and execute that plan when I arrive at the market. These are all routine and common activities, but each involves the directed generation of experiences in ways that manifest an implicit practical understanding of their intentional properties and interconnected contents (Van Gulick 2000).

Consciousness is a dynamic process, and thus an adequate descriptive answer to the What question must deal with more than just its static or momentary properties. In particular, it must give some account of the temporal dynamics of consciousness and the ways in which its self-transforming flow reflects both its intentional coherence and the semantic self-understanding embodied in the organized controls through which conscious minds continually remake themselves as autopoietic systems engaged with their worlds.

A comprehensive descriptive account of consciousness would need to deal with more than just these seven features, but having a clear account of each of them would take us a long way toward answering the “What is consciousness?” question.

5. The explanatory question: How can consciousness exist?

The How question focuses on explanation rather than description. It asks us to explain the basic status of consciousness and its place in nature. Is it a fundamental feature of reality in its own right, or does its existence depend upon other nonconscious items, be they physical, biological, neural or computational? And if the latter, can we explain or understand how the relevant nonconscious items could cause or realize consciousness? Put simply, can we explain how to make something conscious out of things that are not conscious?

5.1 Diversity of explanatory projects

The How question is not a single question, but rather a general family of more specific questions (Van Gulick 1995). They all concern the possibility of explaining some sort or aspect of consciousness, but they vary in their particular explananda, the restrictions on their explanans, and their criteria for successful explanation. For example, one might ask whether we can explain access consciousness computationally by mimicking the requisite access relations in a computational model. Or one might be concerned instead with whether the phenomenal and qualitative properties of a conscious creature's mind can be a priori deduced from a description of the neural properties of its brain processes. Both are versions of the How question, but they ask about the prospects of very different explanatory projects, and thus may differ in their answers (Lycan 1996). It would be impractical, if not impossible, to catalog all the possible versions of the How question, but some of the main options can be listed.

Explananda. Possible explananda would include the various sorts of state and creature consciousness distinguished above, as well as the seven features of consciousness listed in response to the What question. Those two types of explananda overlap and intersect. We might for example aim to explain the dynamic aspect either of phenomenal or of access consciousness. Or we could try to explain the subjectivity of either qualitative or meta-mental consciousness. Not every feature applies to every sort of consciousness, but all apply to several. How one explains a given feature in relation to one sort of consciousness may not correspond with what is needed to explain it relative to another.

Explanans. The range of possible explanans is also diverse. In perhaps its broadest form, the How question asks how consciousness of the relevant sort could be caused or realized by nonconscious items, but we can generate a wealth of more specific questions by further restricting the range of the relevant explanans. One might seek to explain how a given feature of consciousness is caused or realized by underlying neural processes, biological structures, physical mechanisms, functional or teleofunctional relations, computational organization, or even by nonconscious mental states. The prospects for explanatory success will vary accordingly. In general the more limited and elementary the range of the explanans, the more difficult the problem of explaining how could it suffice to produce consciousness (Van Gulick 1995).

Criteria of explanation. The third key parameter is how one defines the criterion for a successful explanation. One might require that the explanandum be a priori deducible from the explanans, although it is controversial whether this is either a necessary or a sufficient criterion for explaining consciousness (Jackson 1993). Its sufficiency will depend in part on the nature of the premises from which the deduction proceeds. As a matter of logic, one will need some bridge principles to connect propositions or sentences about consciousness with those that do not mention it. If one's premises concern physical or neural facts, then one will need some bridge principles or links that connect such facts with facts about consciousness (Kim 1998). Brute links, whether nomic or merely well confirmed correlations, could provide a logically sufficient bridge to infer conclusions about consciousness. But they would probably not allow us to see how or why those connections hold, and thus they would fall short of fully explaining how consciousness exists (Levine 1983, 1993, McGinn 1991).

One could legitimately ask for more, in particular for some account that made intelligible why those links hold and perhaps why they could not fail to do so. A familiar two-stage model for explaining macro-properties in terms of micro-substrates is often invoked. In the first step, one analyzes the macro-property in terms of functional conditions, and then in the second stage one shows that the micro-structures obeying the laws of their own level nomically suffice to guarantee the satisfaction of the relevant functional conditions (Armstrong 1968, Lewis 1972).

The micro-properties of collections of H2O molecules at 20°C suffice to satisfy the conditions for the liquidity of the water they compose. Moreover, the model makes intelligible how the liquidity is produced by the micro-properties. A satisfactory explanation of how consciousness is produced might seem to require a similar two stage story. Without it, even a priori deducibility might seem explanatorily less than sufficient, though the need for such a story remains a matter of controversy (Block and Stalnaker 1999, Chalmers and Jackson 2001).

5.2 The explanatory gap

Our current inability to supply a suitably intelligible link is sometimes described, following Joseph Levine (1983), as the existence of an explanatory gap, and as indicating our incomplete understanding of how consciousness might depend upon a nonconscious substrate, especially a physical substrate. The basic gap claim admits of many variations in generality and thus in strength.

In perhaps its weakest form, it asserts a practical limit on our present explanatory abilities; given our current theories and models we can not now articulate an intelligible link. A stronger version makes an in principle claim about our human capacities and thus asserts that given our human cognitive limits we will never be able to bridge the gap. To us, or creatures cognitively like us, it must remain a residual mystery (McGinn 1991). Colin McGinn (1995) has argued that given the inherently spatial nature of both our human perceptual concepts and the scientific concepts we derive from them, we humans are not conceptually suited for understanding the nature of the psychophysical link. Facts about that link are as cognitively closed to us as are facts about multiplication or square roots to armadillos. They do not fall within our conceptual and cognitive repertoire. An even stronger version of the gap claim removes the restriction to our cognitive nature and denies in principle that the gap can be closed by any cognitive agents.

Those who assert gap claims disagree among themselves about what metaphysical conclusions, if any, follow from our supposed epistemic limits. Levine himself has been reluctant to draw any anti-physicalist ontological conclusions (Levine 1993, 2001). On the other hand some neodualists have tried to use the existence of the gap to refute physicalism (Foster 1996, Chalmers 1996). The stronger one's epistemological premise, the better the hope of deriving a metaphysical conclusion. Thus unsurprisingly, dualist conclusions are often supported by appeals to the supposed impossibility in principle of closing the gap.

If one could see on a priori grounds that there is no way in which consciousness could be intelligibly explained as arising from the physical, it would not be a big step to concluding that it in fact does not do so (Chalmers 1996). However, the very strength of such an epistemological claim makes it difficult to assume with begging the metaphysical result in question. Thus those who wish to use a strong in principle gap claim to refute physicalism must find independent grounds to support it. Some have appealed to conceivability arguments for support, such as the alleged conceivability of zombies molecularly identical with conscious humans but devoid of all phenomenal consciousness (Campbell 1970, Kirk 1974, Chalmers 1996). Other supporting arguments invoke the supposed non-functional nature of consciousness and thus its alleged resistance to the standard scientific method of explaining complex properties (e.g., genetic dominance) in terms of physically realized functional conditions (Block 1980a, Chalmers 1996). Such arguments avoid begging the anti-physicalist question, but they themselves rely upon claims and intuitions that are controversial and not completely independent of one's basic view about physicalism. Discussion on the topic remains active and ongoing.

Our present inability to see any way of closing the gap may exert some pull on our intuitions, but it may simply reflect the limits of our current theorizing rather than an unbridgeable in principle barrier (Dennett 1991). Moreover, some physicalists have argued that explanatory gaps are to be expected and are even entailed by plausible versions of ontological physicalism, ones that treat human agents as physically realized cognitive systems with inherent limits that derive from their evolutionary origin and situated contextual mode of understanding (Van Gulick 1985, 2003; McGinn 1991, Papineau 1995, 2002). On this view, rather than refuting physicalism, the existence of explanatory gaps may confirm it. Discussion and disagreement on these topics remains active and ongoing.

5.3 Reductive and non-reductive explanation

As the need for intelligible linkage has shown, a priori deducibility is not in itself obviously sufficient for successful explanation (Kim 1980), nor is it clearly necessary. Some weaker logical link might suffice in many explanatory contexts. We can sometimes tell enough of a story about how facts of one sort depend upon those of another to satisfy ourselves that the latter do in fact cause or realize the former even if we can not strictly deduce all the former facts from the latter.

Strict intertheoretical deduction was taken as the reductive norm by the logical empiricist account of the unity of science (Putnam and Oppenheim 1958), but in more recent decades a looser nonreductive picture of relations among the various sciences has gained favor. In particular, nonreductive materialists have argued for the so called “autonomy of the special sciences” (Fodor 1974) and for the view that understanding the natural world requires us to use a diversity of conceptual and representational systems that may not be strictly intertranslatable or capable of being put into the tight correspondence required by the older deductive paradigm of interlevel relations (Putnam 1975).

Economics is often cited as an example (Fodor 1974, Searle 1992). Economic facts may be realized by underlying physical processes, but no one seriously demands that we be able to deduce the relevant economic facts from detailed descriptions of their underlying physical bases or that we be able to put the concepts and vocabulary of economics in tight correspondence with those of the physical sciences.

Nonetheless our deductive inability is not seen as cause for ontological misgivings; there is no “money-matter” problem. All that we require is some general and less than deductive understanding of how economic properties and relations might be underlain by physical ones. Thus one might opt for a similar criterion for interpreting the How question and for what counts as explaining how consciousness might be caused or realized by nonconscious items. However, some critics, such as Kim (1987), have challenged the coherence of any view that aims to be both non-reductive and physicalist, though supporters of such views have replied in turn (Van Gulick 1993).

Others have argued that consciousness is especially resistant to explanation in physical terms because of the inherent differences between our subjective and objective modes of understanding. Thomas Nagel famously argued (1974) that there are unavoidable limits placed on our ability to understand the phenomenology of bat experience by our inability to empathetically take on an experiential perspective like that which characterizes the bat's echo-locatory auditory experience of its world. Given our inability to undergo similar experience, we can have at best partial understanding of the nature of such experience. No amount of knowledge gleaned from the external objective third-person perspective of the natural sciences will supposedly suffice to allow us to understand what the bat can understand of its own experience from its internal first-person subjective point of view.

5.4 Prospects of explanatory success

The How question thus subdivides into a diverse family of more specific questions depending upon the specific sort or feature of consciousness one aims to explain, the specific restrictions one places on the range of the explanans and the criterion one uses to define explanatory success. Some of the resulting variants seem easier to answer than others. Progress may seem likely on some of the so called “easy problems” of consciousness, such as explaining the dynamics of access consciousness in terms of the functional or computational organization of the brain (Baars 1988). Others may seem less tractable, especially the so-called “hard problem” (Chalmers 1995) which is more or less that of giving an intelligible account that lets us see in an intuitively satisfying way how phenomenal or “what it's like” consciousness might arise from physical or neural processes in the brain.

Positive answers to some versions of the How questions seem near at hand, but others appear to remain deeply baffling. Nor should we assume that every version has a positive answer. If dualism is true, then consciousness in at least some of its types may be basic and fundamental. If so,we will not be able to explain how it arises from nonconscious items since it simply does not do so.

One's view of the prospects for explaining consciousness will typically depend upon one's perspective. Optimistic physicalists will likely see current explanatory lapses as merely the reflection of the early stage of inquiry and sure to be remedied in the not too distant future (Dennett 1991, Searle 1992, P. M.Churchland 1995). To dualists, those same impasses will signify the bankruptcy of the physicalist program and the need to recognize consciousness as a fundamental constituent of reality in its own right (Robinson 1982, Foster 1989, 1996, Chalmers 1996). What one sees depends in part on where one stands, and the ongoing project of explaining consciousness will be accompanied by continuing debate about its status and prospects for success.

6. The functional question: Why does consciousness exist?

The functional or Why question asks about the value or role or consciousness and thus indirectly about its origin. Does it have a function, and if so what is it? Does it make a difference to the operation of systems in which it is present, and if so why and how? If consciousness exists as a complex feature of biological systems, then its adaptive value is likely relevant to explaining its evolutionary origin, though of course its present function, if it has one, need not be the same as that it may have had when it first arose. Adaptive functions often change over biological time. Questions about the value of consciousness also have a moral dimension in at least two ways. We are inclined to regard an organism's moral status as at least partly determined by the nature and extent to which it is conscious, and conscious states, especially conscious affective states such as pleasures and pains, play a major role in many of the accounts of value that underlie moral theory (Singer 1975).

As with the What and How questions, the Why question poses a general problem that subdivides into a diversity of more specific inquiries. In so far as the various sorts of consciousness, e.g., access, phenomenal, meta-mental, are distinct and separable—which remains an open question—they likely also differ in their specific roles and values. Thus the Why question may well not have a single or uniform answer.

6.1 Causal status of consciousness

Perhaps the most basic issue posed by any version of the Why question is whether or not consciousness of the relevant sort has any causal impact at all. If it has no effects and makes no causal difference whatsoever, then it would seem unable to play any significant role in the systems or organisms in which it is present, thus undercutting at the outset most inquiries about its possible value. Nor can the threat of epiphenomenal irrelevance be simply dismissed as an obvious non-option, since at least some forms of consciousness have been seriously alleged in the recent literature to lack causal status. (See the entry on epiphenomenalism.) Such worries have been raised especially with regard to qualia and qualitative consciousness (Huxley 1874, Jackson 1982, Chalmers 1996), but challenges have also been leveled against the causal status of other sorts including meta-mental consciousness (Velmans 1991).

Both metaphysical and empirical arguments have been given in support of such claims. Among the former are those that appeal to intuitions about the conceivability and logical possibility of zombies, i.e., of beings whose behavior, functional organization, and physical structure down to the molecular level are identical to those of normal human agents but who lack any qualia or qualitative consciousness. Some (Kirk 1970, Chalmers 1996) assert such beings are possible in worlds that share all our physical laws, but others deny it (Dennett 1991, Levine 2001). If they are possible in such worlds, then it would seem to follow that even in our world, qualia do not affect the course of physical events including those that constitute our human behaviors. If those events unfold in the same way whether or not qualia are present, then qualia appear to be inert or epiphenomenal at least with respect to events in the physical world. However, such arguments and the zombie intuitions on which they rely are controversial and their soundness remains in dispute (Searle 1992, Yablo 1998, Balog 1999).

Arguments of a far more empirical sort have challenged the causal status of meta-mental consciousness, at least in so far as its presence can be measured by the ability to report on one's mental state. Scientific evidence is claimed to show that consciousness of that sort is neither necessary for any type of mental ability nor does it occur early enough to act as a cause of the acts or processes typically thought to be its effects (Velmans 1991). According to those who make such arguments, the sorts of mental abilities that are typically thought to require consciousness can all be realized unconsciously in the absence of the supposedly required self-awareness.

Moreover, even when conscious self-awareness is present, it allegedly occurs too late to be the cause of the relevant actions rather than their result or at best a joint effect of some shared prior cause (Libet 1985). Self-awareness or meta-mental consciousness according to these arguments turns out to be a psychological after-effect rather than an initiating cause, more like a post facto printout or the result displayed on one's computer screen than like the actual processor operations that produce both the computer's response and its display.

Once again the arguments are controversial, and both the supposed data and their interpretation are subjects of lively disagreement (see Flanagan 1992, and commentaries accompanying Velmans 1991). Though the empirical arguments, like the zombie claims, require one to consider seriously whether some forms of consciousness may be less causally potent than is typically assumed, many theorists regard the empirical data as no real threat to the causal status of consciousness.

If the epiphenomenalists are wrong and consciousness, in its various forms, is indeed causal, what sorts of effects does it have and what differences does it make? How do mental processes that involve the relevant sort of consciousness differ form those that lack it? What function(s) might consciousness play? The following six sections (6.2–6.7) discuss some of the more commonly given answers. Though the various functions overlap to some degree, each is distinct, and they differ as well in the sorts of consciousness with which each is most aptly linked.

6.2 Flexible control

Increased flexibility and sophistication of control. Conscious mental processes appear to provide highly flexible and adaptive forms of control. Though unconscious automatic processes can be extremely efficient and rapid, they typically operate in ways that are more fixed and predetermined than those which involve conscious self-awareness (Anderson 1983). Conscious awareness is thus of most importance when one is dealing with novel situations and previously unencountered problems or demands (Penfield 1975, Armstrong 1981).

Standard accounts of skill acquisition stress the importance of conscious awareness during the initial learning phase, which gradually gives way to more automatic processes of the sort that require little attention or conscious oversight (Schneider and Shiffrin 1977). Conscious processing allows for the construction or compilation of specifically tailored routines out of elementary units as well as for the deliberate control of their execution.

There is a familiar tradeoff between flexibility and speed; controlled conscious processes purchase their customized versatility at the price of being slow and effortful in contrast to the fluid rapidity of automatic unconscious mental operations (Anderson 1983). The relevant increases in flexibility would seem most closely connected with the meta-mental or higher-order form of consciousness in so far as the enhanced ability to control processes depends upon greater self-awareness. However, flexibility and sophisticated modes of control may be associated as well with the phenomenal and access forms of consciousness.

6.3 Social coordination

Enhanced capacity for social coordination. Consciousness of the meta-mental sort may well involve not only an increase in self-awareness but also an enhanced understanding of the mental states of other minded creatures, especially those of other members of one's social group (Humphreys 1982). Creatures that are conscious in the relevant meta-mental sense not only have beliefs, motives, perceptions and intentions but understand what it is to have such states and are aware of both themselves and others as having them.

This increase in mutually shared knowledge of each other's minds, enables the relevant organisms to interact, cooperate and communicate in more advanced and adaptive ways. Although meta-mental consciousness is the sort most obviously linked to such a socially coordinative role, narrative consciousness of the kind associated with the stream of consciousness is also clearly relevant in so far as it involves the application to one's own case of the interpretative abilities that derive in part from their social application (Ryle 1949, Dennett 1978, 1992).

6.4 Integrated representation

More unified and densely integrated representation of reality. Conscious experience presents us with a world of objects independently existing in space and time. Those objects are typically present to us in a multi-modal fashion that involves the integration of information from various sensory channels as well as from background knowledge and memory. Conscious experience presents us not with isolated properties or features but with objects and events situated in an ongoing independent world, and it does so by embodying in its experiential organization and dynamics the dense network of relations and interconnections that collectively constitute the meaningful structure of a world of objects (Kant 1787, Husserl 1913, Campbell 1997).

Of course, not all sensory information need be experienced to have an adaptive effect on behavior. Adaptive non-experiential sensory-motor links can be found both in simple organisms, as well as in some of the more direct and reflexive processes of higher organisms. But when experience is present, it provides a more unified and integrated representation of reality, one that typically allows for more open-ended avenues of response (Lorenz 1977). Consider for example the representation of space in an organism whose sensory input channels are simply linked to movement or to the orientation of a few fixed mechanisms such as those for feeding or grabbing prey, and compare it with that in an organism capable of using its spatial information for flexible navigation of its environment and for whatever other spatially relevant aims or goals it may have, as when a person visually scans her office or her kitchen (Gallistel 1990).

It is representation of this latter sort that is typically made available by the integrated mode of presentation associated with conscious experience. The unity of experienced space is just one example of the sort of integration associated with our conscious awareness of an objective world. (See the entry on unity of consciousness.)

This integrative role or value is most directly associated with access consciousness, but also clearly with the larger phenomenal and intentional structure of experience. It is relevant even to the qualitative aspect of consciousness in so far as qualia play an important role in our experience of unified objects in a unified space or scene. It is intimately tied as well to the transparency of experience described in response to the What question, especially to semantic transparency (Van Gulick 1993). Integration of information plays a major role in several current neuro-cognitive theories of consciousness especially Global Workspace theories (see section 9.5) and Giulio Tononi's Integrated Information theory. (section 9.6 below).

6.5 Informational access

More global informational access. The information carried in conscious mental states is typically available for use by a diversity of mental subsystems and for application to a wide range of potential situations and actions (Baars 1988). Nonconscious information is more likely to be encapsulated within particular mental modules and available for use only with respect to the applications directly connected to that subsystem's operation (Fodor 1983). Making information conscious typically widens the sphere of its influence and the range of ways it which it can be used to adaptively guide or shape both inner and outer behavior. A state's being conscious may be in part a matter of what Dennett calls “cerebral celebrity”, i.e., of its ability to have a content-appropriate impact on other mental states.

This particular role is most directly and definitionally tied to the notion of access consciousness (Block 1995), but meta-mental consciousness as well as the phenomenal and qualitative forms all seem plausibly linked to such increases in the availability of information (Armstrong 1981, Tye 1985). Diverse cognitive and neuro-cognitive theories incorporate access as a central feature of consciousness and conscious processing. Global Workspace theories, Prinz's Attendend Intermediate Representation (AIR) (Prinz 2012) and Tononi's Integrated Information Theory (IIT) all distinguish conscious states and processes at least partly in terms of enhanced wide spread access to the state's content (See section 9.6)

6.6 Freedom of will

Increased freedom of choice or free will. The issue of free will remains a perennial philosophical problem, not only with regard to whether or not it exists but even as to what it might or should consist in (Dennett 1984, van Inwagen 1983, Hasker 1999, Wegner 2002). (See the entry on free will.) The notion of free will may itself remain too murky and contentious to shed any clear light on the role of consciousness, but there is a traditional intuition that the two are deeply linked.

Consciousness has been thought to open a realm of possibilities, a sphere of options within which the conscious self might choose or act freely. At a minimum, consciousness might seem a necessary precondition for any such freedom or self-determination (Hasker 1999). How could one engage in the requisite sort of free choice, while remaining solely within the unconscious domain? How can one determine one's own will without being conscious of it and of the options one has to shape it.

The freedom to chose one's actions and the ability to determine one's own nature and future development may admit of many interesting variations and degrees rather than being a simple all or nothing matter, and various forms or levels of consciousness might be correlated with corresponding degrees or types of freedom and self-determination (Dennett 1984, 2003). The link with freedom seems strongest for the meta-mental form of consciousness given its emphasis on self-awareness, but potential connections also seem possible for most of the other sorts as well.

6.7 Intrinsic motivation

Intrinsically motivating states. At least some conscious states appear to have the motive force they do intrinsically. In particular, the functional and motivational roles of conscious affective states, such as pleasures and pains, seem intrinsic to their experiential character and inseparable from their qualitative and phenomenal properties, though the view has been challenged (Nelkin 1989, Rosenthal 1991). The attractive positive motivational aspect of a pleasure seems a part of its directly experienced phenomenal feel, as does the negative affective character of a pain, at least in the case of normal non-pathological experience.

There is considerable disagreement about the extent to which the feel and motive force of pain can dissociate in abnormal cases, and some have denied the existence of such intrinsically motivating aspects altogether (Dennett 1991). However, at least in the normal case, the negative motivational force of pain seems built right into the feel of the experience itself.

Just how this might be so remains less than clear, and perhaps the appearance of intrinsic and directly experienced motivational force is illusory. But if it is real, then it may be one of the most important and evolutionarily oldest respects in which consciousness makes a difference to the mental systems and processes in which it is present (Humphreys 1992).

Other suggestions have been made about the possible roles and value of consciousness, and these six surely do not exhaust the options. Nonetheless, they are among the most prominent recent hypotheses, and they provide a fair survey of the sorts of answers that have been offered to the Why question by those who believe consciousness does indeed make a difference.

6.8 Constitutive and contingent roles

One further point requires clarification about the various respects in which the proposed functions might answer the Why question. In particular one should distinguish between constitutive cases and cases of contingent realization. In the former, fulfilling the role constitutes being conscious in the relevant sense, while in the latter case consciousness of a given sort is just one way among several in which the requisite role might be realized (Van Gulick 1993).

For example, making information globally available for use by a wide variety of subsystems and behavioral applications may constitute its being conscious in the access sense. By contrast, even if the qualitative and phenomenal forms of consciousness involve a highly unified and densely integrated representation of objective reality, it may be possible to produce representations having those functional characteristics but which are not qualitative or phenomenal in nature.

The fact that in us the modes of representation with those characteristics also have qualitative and phenomenal properties may reflect contingent historical facts about the particular design solution that happened to arise in our evolutionary ancestry. If so, there may be quite other means of achieving a comparable result without qualitative or phenomenal consciousness. Whether this is the right way to think about phenomenal and qualitative conscious is unclear; perhaps the tie to unified and densely integrated representation is in fact as intimate and constitutive as it seems to be in the case of access consciousness (Carruthers 2000). Regardless of how that issue gets resolved, it is important to not to conflate constitution accounts with contingent realization accounts when addressing the function of consciousness and answering the question of why it exists (Chalmers 1996).

7. Theories of consciousness

In response to the What, How and Why questions many theories of consciousness have been proposed in recent years. However, not all theories of consciousness are theories of the same thing. They vary not only in the specific sorts of consciousness they take as their object, but also in their theoretical aims.

Perhaps the largest division is between general metaphysical theories that aim to locate consciousness in the overall ontological scheme of reality and more specific theories that offer detailed accounts of its nature, features and role. The line between the two sorts of theories blurs a bit, especially in so far as many specific theories carry at least some implicit commitments on the more general metaphysical issues. Nonetheless, it is useful to keep the division in mind when surveying the range of current theoretical offerings.

8. Metaphysical theories of consciousness

General metaphysical theories offer answers to the conscious version of the mind-body problem, “What is the ontological status of consciousness relative to the world of physical reality?” The available responses largely parallel the standard mind-body options including the main versions of dualism and physicalism.

8.1 Dualist theories

Dualist theories regard at least some aspects of consciousness as falling outside the realm of the physical,but specific forms of dualism differ in just which aspects those are. (See the entry on dualism.)

Substance dualism, such as traditional Cartesian dualism (Descartes 1644), asserts the existence of both physical and non-physical substances. Such theories entail the existence of non-physical minds or selves as entities in which consciousness inheres. Though substance dualism is at present largely out of favor, it does have some contemporary proponents (Swinburne 1986, Foster 1989, 1996).

Property dualism in its several versions enjoys a greater level of current support. All such theories assert the existence of conscious properties that are neither identical with nor reducible to physical properties but which may nonetheless be instantiated by the very same things that instantiate physical properties. In that respect they might be classified as dual aspect theories. They take some parts of reality—organisms, brains, neural states or processes—to instantiate properties of two distinct and disjoint sorts: physical ones and conscious, phenomenal or qualitative ones. Dual aspect or property dualist theories can be of at least three different types.

Fundamental property dualism regards conscious mental properties as basic constituents of reality on a par with fundamental physical properties such as electromagnetic charge. They may interact in causal and law-like ways with other fundamental properties such as those of physics, but ontologically their existence is not dependent upon nor derivative from any other properties (Chalmers 1996).

Emergent property dualism treats conscious properties as arising from complex organizations of physical constituents but as doing so in a radical way such that the emergent result is something over and above its physical causes and is not a priori predictable from nor explicable in terms of their strictly physical natures. The coherence of such emergent views has been challenged (Kim 1998) but they have supporters (Hasker 1999).

Neutral monist property dualism treats both conscious mental properties and physical properties as in some way dependent upon and derivative from a more basic level of reality, that in itself is neither mental nor physical (Russell 1927, Strawson 1994). However, if one takes dualism to be a claim about there being two distinct realms of fundamental entities or properties, then perhaps neutral monism should not be classified as a version of property dualism in so far as it does not regard either mental or physical properties as ultimate or fundamental.

Panpsychism might be regarded as a fourth type of property dualism in that it regards all the constituents of reality as having some psychic, or at least proto-psychic, properties distinct from whatever physical properties they may have (Nagel 1979). Indeed neutral monism might be consistently combined with some version of panprotopsychism (Chalmers 1996) according to which the proto-mental aspects of micro-constituents can give rise under suitable conditions of combination to full blown consciousness. (See the entry on panpsychism.)

The nature of the relevant proto-psychic aspect remains unclear, and such theories face a dilemma if offered in hope of answering the Hard Problem. Either the proto-psychic properties involve the sort of qualitative phenomenal feel that generates the Hard Problem or they do not. If they do, it is difficult to understand how they could possibly occur as ubiquitous properties of reality. How could an electron or a quark have any such experiential feel? However, if the proto-psychic properties do not involve any such feel, it is not clear how they are any better able than physical properties to account for qualitative consciousness in solving the Hard Problem.

A more modest form of panpsychism has been advocated by the neuroscientist Giulio Tononi (2008) and endorsed by other neuroscientists including Christof Koch (2012). This version derives from Tononi's integrated information theory (IIT) of consciousness that identifies consciousness with integrated information which can exist in many degrees (see section 9.6 below). According to IIT, even a simple indicator device such as a single photo diode possesses some degree of integrated information and thus some limited degree of consciousness, a consequence which both Tononi and Koch embrace as a form of panpsychism.

A variety of arguments have been given in favor of dualist and other anti-physicalist theories of consciousness. Some are largelya priori in nature such as those that appeal to the supposed conceivability of zombies (Kirk 1970, Chalmers 1996) or versions of the knowledge argument (Jackson 1982, 1986) which aim to reach an anti-physicalist conclusion about the ontology of consciousness from the apparent limits on our ability to fully understand the qualitative aspects of conscious experience through third-person physical accounts of the brain processes. (See Jackson 1998, 2004 for a contrary view; see also entries on Zombies, and Qualia: The Knowledge Argument) Other arguments for dualism are made on more empirical grounds, such as those that appeal to supposed causal gaps in the chains of physical causation in the brain (Eccles and Popper 1977) or those based on alleged anomalies in the temporal order of conscious awareness (Libet 1982, 1985). Dualist arguments of both sorts have been much disputed by physicalists (P.S. Churchland 1981, Dennett and Kinsbourne 1992).

8.2 Physicalist theories

Most other metaphysical theories of consciousness are versions of physicalism of one familiar sort or another.

Eliminativist theories reductively deny the existence of consciousness or at least the existence of some of its commonly accepted sorts or features. (See the entry on eliminative materialism.) The radical eliminativists reject the very notion of consciousness as muddled or wrong headed and claim that the conscious/nonconscious distinction fails to cut mental reality at its joints (Wilkes 1984, 1988). They regard the idea of consciousness as sufficiently off target to merit elimination and replacement by other concepts and distinctions more reflective of the true nature of mind (P. S. Churchland 1983).

Most eliminativists are more qualified in their negative assessment. Rather than rejecting the notion outright, they take issue only with some of the prominent features that it is commonly thought to involve, such as qualia (Dennett 1990, Carruthers 2000), the conscious self (Dennett 1992), or the so called “Cartesian Theater” where the temporal sequence of conscious experience gets internally projected (Dennett and Kinsbourne 1992). More modest eliminativists, like Dennett, thus typically combine their qualified denials with a positive theory of those aspects of consciousness they take as real, such as the Multiple Drafts Model (section 9.3 below).

Identity theory, at least strict psycho-physical type-type identity theory, offers another strongly reductive option by identifying conscious mental properties, states and processes with physical ones, most typically of a neural or neurophysiological nature. If having a qualitative conscious experience of phenomenal red just is being in a brain state with the relevant neurophysiological properties, then such experiential properties are real but their reality is a straight forwardly physical reality.

Type-type identity theory is so called because it identifies mental and physical types or properties on a par with identifying the property of being water with the property of being composed of H2O molecules. After a brief period of popularity in the early days of contemporary physicalism during the 1950s and 60s (Place 1956, Smart 1959) it has been far less widely held because of problems such as the multiple realization objection according to which mental properties are more abstract and thus capable of being realized by many diverse underlying structural or chemical substrates (Fodor 1974, Hellman and Thompson 1975). If one and the same conscious property can be realized by different neurophysiological (or even non-neurophysiological) properties in different organisms, then the two properties can not be strictly identical.

Nonetheless the type-type identity theory has enjoyed a recent if modest resurgence at least with respect to qualia or qualitative conscious properties. This has been in part because treating the relevant psycho-physical link as an identity is thought by some to offer a way of dissolving the explanatory gap problem (Hill and McLaughlin 1998, Papineau 1995, 2003). They argue that if the conscious qualitative property and the neural property are identical, then there is no need to explain how the latter causes or gives rise to the former. It does not cause it, it is it. And thus there is no gap to bridge, and no further explanation is needed. Identities are not the sort of thing that can be explained, since nothing is identical with anything but itself, and it makes no sense to ask why something is identical with itself.

However, others contend that the appeal to type-type identity does not so obviously void the need for explanation (Levine 2001). Even if two descriptions or concepts in fact refer to one and the same property, one may still reasonably expect some explanation of that convergence, some account of how they pick out one and the same thing despite not initially or intuitively seeming to do so. In other cases of empirically discovered property identities, such as that of heat and kinetic energy, there is a story to be told that explains the co-referential convergence, and it seems fair to expect the same in the psycho-physical case. Thus appealing to type-type identities may not in itself suffice to dissolve the explanatory gap problem.

Most physicalist theories of consciousness are neither eliminativist nor based on strict type-type identities. They acknowledge the reality of consciousness but aim to locate it within the physical world on the basis of some psycho-physical relation short of strict property identity.

Among the common variants are those that take conscious reality to supervene on the physical, be composed of the physical, or be realized by the physical.

Functionalist theories in particular rely heavily on the notion of realization to explicate the relation between consciousness and the physical. According to functionalism, a state or process counts as being of a given mental or conscious type in virtue of the functional role it plays within a suitably organized system (Block 1980a). A given physical state realizes the relevant conscious mental type by playing the appropriate role within the larger physical system that contains it. (See the entry on functionalism.) The functionalist often appeals to analogies with other inter-level relations, as between the biological and biochemical or the chemical and the atomic. In each case properties or facts at one level are realized by complex interactions between items at an underlying level.

Critics of functionalism often deny that consciousness can be adequately explicated in functional terms (Block 1980a, 1980b, Levine 1983, Chalmers 1996). According to such critics, consciousness may have interesting functional characteristics but its nature is not essentially functional. Such claims are sometimes supported by appeal to the supposed possibility of absent or inverted qualia, i.e., the possibility of beings who are functionally equivalent to normal humans but who have reversed qualia or none at all. The status of such possibilities is controversial (Shoemaker 1981, Dennett 1990, Carruthers 2000), but if accepted they would seem to pose a problem for the functionalist. (See the entry on qualia.)

Those who ground ontological physicalism on the realization relation often combine it with a nonreductive view at the conceptual or representational level that stresses the autonomy of the special sciences and the distinct modes of description and cognitive access they provide.

Non-reductive physicalism of this sort denies that the theoretical and conceptual resources appropriate and adequate for dealing with facts at the level of the underlying substrate or realization level must be adequate as well for dealing with those at the realized level (Putnam 1975, Boyd 1980). As noted above in response to the How question, one can believe that all economic facts are physically realized without thinking that the resources of the physical sciences provide all the cognitive and conceptual tools we need for doing economics (Fodor 1974).

Nonreductive physicalism has been challenged for its alleged failure to “pay its physicalist dues” in reductive coin. It is faulted for supposedly not giving an adequate account of how conscious properties are or could be realized by underlying neural, physical or functional structures or processes (Kim 1987, 1998). Indeed it has been charged with incoherence because of its attempt to combine a claim of physical realization with the denial of the ability to spell out that relation in a strict and a priori intelligible way (Jackson 2004).

However, as noted above in discussion of the How question, nonreductive physicalists reply by agreeing that some account of psycho-physical realization is indeed needed, but adding that the relevant account may fall far short of a priori deducibility, yet still suffice to satisfy our legitimate explanatory demands (McGinn 1991, Van Gulick 1985). The issue remains under debate.

9. Specific Theories of Consciousness

Although there are many general metaphysical/ontological theories of consciousness, the list of specific detailed theories about its nature is even longer and more diverse. No brief survey could be close to comprehensive, but seven main types of theories may help to indicate the basic range of options: higher-order theories, representational theories, interpretative narrative theories, cognitive theories, neural theories, quantum theories and nonphysical theories. The categories are not mutually exclusive; for example, many cognitive theories also propose a neural substrate for the relevant cognitive processes. Nonetheless grouping them in the seven classes provides a basic overview.

9.1 Higher-order theories

Higher-order (HO) theories analyze the notion of a conscious mental state in terms of reflexive meta-mental self-awareness. The core idea is that what makes a mental state M a conscious mental state is the fact that it is accompanied by a simultaneous and non-inferential higher-order (i.e., meta-mental) state whose content is that one is now in M. Having a conscious desire for some chocolate involves being in two mental states; one must have both a desire for some chocolate and also a higher-order state whose content is that one is now having just such a desire. Unconscious mental states are unconscious precisely in that we lack the relevant higher-order states about them. Their being unconscious consists in the fact that we are not reflexively and directly aware of being in them. (See the entry on higher-order theories of consciousness.)

Higher-order theories come in two main variants that differ concerning the psychological mode of the relevant conscious-making meta-mental states. Higher-order thought (HOT) theories take the required higher-order state to be an assertoric thought-like meta-state (Rosenthal 1986, 1993). Higher-order perception (HOP) theories take them to be more perception-like and associated with a kind of inner sense and intra-mental monitoring systems of some sort (Armstrong 1981, Lycan 1987, 1996).

Each has its relative strengths and problems. HOT theorists note that we have no organs of inner sense and claim that we experience no sensory qualities other than those presented to us by outer directed perception. HOP theorists on the other hand can argue that their view explains some of the additional conditions required by HO accounts as natural consequences of the perception-like nature of the relevant higher-order states. In particular the demands that the conscious-making meta-state be noninferential and simultaneous with its lower level mental object might be explained by the parallel conditions that typically apply to perception. We perceive what is happening now, and we do so in a way that involves no inferences, at least not any explicit personal-level inferences. Those conditions are no less necessary on the HOT view but are left unexplained by it, which might seem to give some explanatory advantage to the HOP model (Lycan 2004, Van Gulick 2000), though some HOT theorists argue otherwise (Carruthers 2000).

Whatever their respective merits, both HOP and HOT theories face some common challenges, including what might be called thegenerality problem. Having a thought or perception of a given item X—be it a rock, a pen or a potato—does not in general make X a conscious X. Seeing or thinking of the potato on the counter does not make it a conscious potato. Why then should having a thought or perception of a given desire or a memory make it a conscious desire or memory (Dretske 1995, Byrne 1997). Nor will it suffice to note that we do not apply the term “conscious” to rocks or pens that we perceive or think of, but only to mental states that we perceive or think of (Lycan 1997, Rosenthal 1997). That may be true, but what is needed is some account of why it is appropriate to do so.

The higher-order view is most obviously relevant to the meta-mental forms of consciousness, but some of its supporters take it to explain other types of consciousness as well, including the more subjective what it's like and qualitative types. One common strategy is to analyze qualia as mental features that are capable of occurring unconsciously; for example they might be explained as properties of inner states whose structured similarity relations given rise to beliefs about objective similarities in the world (Shoemaker 1975, 1990). Though unconscious qualia can play that functional role, there need be nothing that it is like to be in a state that has them (Nelkin 1989, Rosenthal 1991, 1997). According to the HO theorist, what-it's-likeness enters only when we become aware of that first-order state and its qualitative properties by having an appropriate meta-state directed at it.

Critics of the HO view have disputed that account, and some have argued that the notion of unconscious qualia on which it relies is incoherent (Papineau 2002). Whether or not such proposed HO accounts of qualia are successful, it is important to note that most HO advocates take themselves to be offering a comprehensive theory of consciousness, or at least the core of such a general theory, rather than merely one limited to some special meta-mental forms of it.

Other variants of HO theory go beyond the standard HOT and HOP versions including some that analyze consciousness in terms of dispositional rather than occurrent higher-order thoughts (Carruthers 2000). Others appeal to implicit rather than explicit higher-order understanding and weaken or remove the standard assumption that the meta-state must be distinct and separate from its lower-order object (Gennaro 1995, Van Gulick 2000, 2004) with such views overlapping with so called reflexive theories discussed in the section. Other variants of HO theory continue to be offered, and debate between supporters and critics of the basic approach remains active. (See the recent papers in Gennaro 2004.)

9.2 Reflexive theories

Reflexive theories, like higher-order theories, imply a strong link between consciousness and self-awareness. They differ in that they locate the aspect of self-awareness directly within the conscious state itself rather than in a distinct meta-state directed at it. The idea that conscious states involve a double intentionality goes back at least to Brentano (1874) in the 19th century. The conscious state is intentionally directed at an object outside itself—such as a tree or chair in the case of a conscious perception—as well as intentionally directed at itself. One and the same state is both an outer-directed awareness and an awareness of itself. Several recent theories have claimed that such reflexive awareness is a central feature of conscious mental states. Some view themselves as variants of higher-order theory (Gennaro 2004, 2012) while others reject the higher-order category and describe their theories as presenting a “same-order” account of consciousness as self-awareness (Kriegel 2009). Yet others challenge the level distinction by analyzing the meta-intentional content as implicit in the phenomenal first-order content of conscious states, as in so called Higher-Order Global State models (HOGS) (Van Gulick 2004,2006). A sample of papers, some supporting and some attacking the reflexive view can be found in Krigel and Williford (2006).

9.3 Representationalist theories

Almost all theories of consciousness regard it as having representational features, but so called representationalist theories are defined by the stronger view that its representational features exhaust its mental features (Harman 1990, Tye 1995, 2000). According to the representationalist, conscious mental states have no mental properties other than their representational properties. Thus two conscious or experiential states that share all their representational properties will not differ in any mental respect.

The exact force of the claim depends on how one interprets the idea of being “representationally the same” for which there are many plausible alternative criteria. One could define it coarsely in terms of satisfaction or truth conditions, but understood in that way the representationalist thesis seems clearly false. There are too many ways in which states might share their satisfaction or truth conditions yet differ mentally, including those that concern their mode of conceptualizing or presenting those conditions.

At the opposite extreme, one could count two states as representationally distinct if they differed in any features that played a role in their representational function or operation. On such a liberal reading any differences in the bearers of content would count as representational differences even if they bore the same intentional or representational content; they might differ only in their means or mode of representation not their content.

Such a reading would of course increase the plausibility of the claim that a conscious state's representational properties exhaust its mental properties but at the cost of significantly weakening or even trivializing the thesis. Thus the representationalist seems to need an interpretation of representational sameness that goes beyond mere satisfaction conditions and reflects all the intentional or contentful aspects of representation without being sensitive to mere differences in underlying non-contentful features of the processes at the realization level. Thus most representationalists provide conditions for conscious experience that include both a content condition plus some further causal role or format requirements (Tye 1995, Dretske 1995, Carruthers 2000). Other representationalists accept the existence of qualia but treat them as objective properties that external objects are represented as having, i.e., they treat them as represented properties rather than as properties of representations or mental states (Dretske 1995, Lycan 1996).

Representationalism can be understood as a qualified form of eliminativism insofar as it denies the existence of properties of a sort that conscious mental states are commonly thought to have—or at least seem to have—namely those that are mental but not representational. Qualia, at least if understood as intrinsic monadic properties of conscious states accessible to introspection, would seem to be the most obvious targets for such elimination. Indeed part of the motivation for representationalism is to show that one can accommodate all the facts about consciousness, perhaps within a physicalist framework, without needing to find room for qualia or any other apparently non-representational mental properties (Dennett 1990, Lycan 1996, Carruthers 2000).

Representationalism has been quite popular in recent years and had many defenders, but it remains highly controversial and intuitions clash about key cases and thought experiments (Block 1996). In particular the possibility of inverted qualia provides a crucial test case. To anti-representationalists, the mere logical possibility of inverted qualia shows that conscious states can differ in a significant mental respect while coinciding representationally. Representationalists in reply deny either the possibility of such inversion or its alleged import (Dretske 1995, Tye 2000).

Many other arguments have been made for and against representationalism, such as those concerning perceptions in different sense modalities of one and the same state of affairs—seeing and feeling the same cube—which might seem to involve mental differences distinct from how the relevant states represent the world to be (Peacocke 1983, Tye 2003). In each case, both sides can muster strong intuitions and argumentative ingenuity. Lively debate continues.

9.4 Narrative Interpretative Theories

Some theories of consciousness stress the interpretative nature of facts about consciousness. According to such views, what is or is not conscious is not always a determinate fact, or at least not so independent of a larger context of interpretative judgments. The most prominent philosophical example is the Multiple Drafts Model (MDM) of consciousness, advanced by Daniel Dennett (1991). It combines elements of both representationalism and higher-order theory but does so in a way that varies interestingly from the more standard versions of either providing a more interpretational and less strongly realist view of consciousness.

The MDM includes many distinct but interrelated features. Its name reflects the fact that at any given moment content fixations of many sorts are occurring throughout the brain. What makes some of these contents conscious is not that they occur in a privileged spatial or functional location—the so called “Cartesian Theater”—nor in a special mode or format, all of which the MDM denies. Rather it a matter of what Dennett calls “cerebral celebrity”, i.e., the degree to which a given content influences the future development of other contents throughout the brain, especially with regard to how those effects are manifest in the reports and behaviors that the person makes in response to various probes that might indicate her conscious state. One of the MDM's key claims is that different probes (e. g., being asked different questions or being in different contexts that make differing behavioral demands) may elicit different answers about the person's conscious state. Moreover, according to the MDM there may be no probe-independent fact of the matter about what the person's conscious state really was. Hence the “multiple” of the Multiple Drafts Model.

The MDM is representationalist in that it analyzes consciousness in terms of content relations. It also denies the existence of qualia and thus rejects any attempt to distinguish conscious states from nonconscious states by their presence. It rejects as well the notion of the self as an inner observer, whether located in the Cartesian Theater or elsewhere. The MDM treats the self as an emergent or virtual aspect of the coherent roughly serially narrative that is constructed through the interactive play of contents in the system. Many of those contents are bound together at the intentional level as perceptions or fixations from a relatively unified and temporally extended point of view, i.e., they cohere in their contents as if they were the experiences of a ongoing self. But it is the order of dependence that is crucial to the MDM account. The relevant contents are not unified because they are all observed by a single self, but just the converse. It is because they are unified and coherent at the level of content that they count as the experiences of a single self, at least of a single virtual self.

It is in this respect that the MDM shares some elements with higher-order theories. The contents that compose the serial narrative are at least implicitly those of an ongoing if virtual self, and it is they that are most likely to be expressed in the reports the person makes of her conscious state in response to various probes. They thus involve a certain degree of reflexivity or self-awareness of the sort that is central to higher-order theories, but the higher-order aspect is more an implicit feature of the stream of contents rather than present in distinct explicit higher-order states of the sort found in standard HO theories.

Dennett's MDM has been highly influential but has also drawn criticism, especially from those who find it insufficiently realist in its view of consciousness and at best incomplete in achieving its stated goal to fully explain it (Block 1994, Dretske 1994, Levine 1994). Many of its critics acknowledge the insight and value of the MDM, but deny that there are no real facts of consciousness other than those captured by it (Rosenthal 1994, Van Gulick 1994, Akins 1996).

From a more empirical perspective, the neuroscientist Michael Gazzaniga (2011) has introduced the idea of an “interpreter module” based in the left hemisphere that makes sense of our actions in any inferential way and constructs an ongoing narrative of our actions and experience. Though the theory is not intended as a complete theory of consciousness, it accords a major role to such interpretative narrative activity.

9.5 Cognitive Theories

A number theories of consciousness associate it with a distinct cognitive architecture or with a special pattern of activity with that structure.

Global Workspace. A major psychological example of the cognitive approach is the Global Workspace theory. As initially developed by Bernard Baars (1988)) global workspace theory describes consciousness in terms of a competition among processors and outputs for a limited capacity resource that “broadcasts” information for widespread access and use. Being available in that way to the global workspace makes information conscious at least in the access sense. It is available for report and the flexible control of behavior. Much like Dennett's “cerebral celebrity”, being broadcast in the workspace makes contents more accessible and influential with respect to other contents and other processors. At the same time the original content is strengthened by recurrent support back from the workspace and from other contents with which it coheres. The capacity limits on the workspace correspond to the limits typically placed on focal attention or working memory in many cognitive models.

The model has been further developed with proposed connections to particular neural and functional brain systems by Stanislas Dehaene and others (2000). Of special importance is the claim that consciousness in both the access and phenomenal sense occurs when and only when the relevant content enters the larger global network involving both primary sensory areas as well as many other areas including frontal and parietal areas associated with attention. Dehaene claims that conscious perception begins only with the “ignition” of that larger global network; activity in the primary sensory areas will not suffice no matter how intense or recurrent (though see the contrary view of Victor Lamme in section 9.7).

Attended Intermediate Representation. Another cognitive theory is Jesse Prinz's (2012) Attended Intermediate level Representation theory (AIR). The theory is a neuro-cognitive hybrid account of conscious. According to AIR theory, a conscious perception must meet both cognitive and neural conditions. It must be a representation of a perceptually intermediate property which Prinz argues are the only properties of which we are aware in conscious experience—we experience only basic features of external objects such as colors, shapes, tones, and feels. According to Prinz, our awareness of higher level properties—such as being a pine tree or my car keys—is wholly a matter of judging and not of conscious experience. Hence the Intermediate Representational (IR) aspect of AIR. To be conscious such a represented content must also be Attended (the A aspect of AIR). Prinz proposes a particular neural substrate for each component. He identifies the intermediate level representations with gamma (40–80hz) vector activity in sensory cortex and the attentional component with synchronized oscillations that can incorporate that gamma vector activity.

9.6 Information Integration Theory

The integration of information from many sources is an important feature of consciousness and, as noted above (section 6.4), is often cited as one of its major functions. Content integration plays an important role in various theories especially global workspace theory (section 9.3). However, a proposal by the neuroscientist Giulio Tononi (2008) goes further in identifying consciousness with integrated information and asserting that information integration of the relevant sort is both necessary and sufficient for consciousness regardless of the substrate in which it is realized (which need not be neural or biological). According to Tononi's Integrated Information Theory (IIT), consciousness is a purely information-theoretic property of systems. He proposes a mathematical measure φ that aims to measure not merely the information in the parts of a given system but also the information contained in the organization of the system over and above that in its parts. φ thus corresponds to the system's degree of informational integration. Such a system can contain many overlapping complexes and the complex with the highest φ value will be conscious according to IIT.

According to IIT, consciousness varies in quantity and comes in many degrees which correspond to φ values. Thus even a simple system such a single photo diode will be conscious to some degree if it is not contained within a larger complex. In that sense, IIT implies a form of panpsychism that Tononi explicitly endorses. According to IIT, the quality of the relevant consciousness is determined by the totality of informational relations within the relevant integrated complex. Thus IIT aims to explain both the quantity and quality of phenomenal consciousness. Other neuroscientists, notably Christof Koch, have also endorsed the IIT approach (Koch 2012).

9.7 Neural Theories

Neural theories of consciousness come in many forms, though most in some way concern the so called “neural correlates of consciousness” or NCCs. Unless one is a dualist or other non-physicalist, more than mere correlation is required; at least some NCCs must be the essential substrates of consciousness. An explanatory neural theory needs to explain why or how the relevant correlations exist, and if the theory is committed to physicalism that will require showing how the underlying neural substrates could be identical with their neural correlates or at least realize them by satisfying the required roles or conditions (Metzinger 2000).

Such theories are diverse not only in the neural processes or properties to which they appeal but also in the aspects of consciousness they take as their respective explananda. Some are based on high-level systemic features of the brain, but others focus on more specific physiological or structural properties, with corresponding differences in their intended explanatory targets. Most in some way aim to connect with theories of consciousness at other levels of description such as cognitive, representational or higher-order theories.

A sampling of recent neural theories might include models that appeal to global integrated fields (Kinsbourne), binding through synchronous oscillation (Singer 1999, Crick and Koch 1990), NMDA-mediated transient neural assemblies (Flohr 1995), thalamically modulated patterns of cortical activation (Llinas 2001), reentrant cortical loops (Edelman 1989), comparator mechanisms that engage in continuous action-prediction-assessment loops between frontal and midbrain areas (Gray 1995), left hemisphere based interpretative processes (Gazzaniga 1988), and emotive somatosensory hemostatic processes based in the frontal-limbic nexus (Damasio 1999) or in the periaqueductal gray (Panksepp 1998).

In each case the aim is to explain how organization and activity at the relevant neural level could underlie one or another major type or feature of consciousness. Global fields or transient synchronous assemblies could underlie the intentional unity of phenomenal consciousness. NMDA-based plasticity, specific thalamic projections into the cortex, or regular oscillatory waves could all contribute to the formation of short term but widespread neural patterns or regularities needed to knit integrated conscious experience out of the local activity in diverse specialized brain modules. Left hemisphere interpretative processes could provide a basis for narrative forms of conscious self-awareness. Thus it is possible for multiple distinct neural theories to all be true, with each contributing some partial understanding of the links between conscious mentality in its diverse forms and the active brain at its many levels of complex organization and structure.

One particular recent controversy has concerned the issue of whether global or merely local recurrent activity is sufficient for phenomenal consciousness. Supporters of the global neuronal workspace model (Dehaene 2000) have argued that consciousness of any sort can occur only when contents are activated with a large scale pattern of recurrent activity involving frontal and parietal areas as well as primary sensory areas of cortex. Others in particular the psychologist Victor Lamme (2006) and the philosopher Ned Block (2007) have argued that local recurrent activity between higher and lower areas within sensory cortex (e.g. with visual cortex) can suffice for phenomenal consciousness even in the absence of verbal reportability and other indicators of access consciousness.

9.8 Quantum theories

Other physical theories have gone beyond the neural and placed the natural locus of consciousness at a far more fundamental level, in particular at the micro-physical level of quantum phenomena. According to such theories, the nature and basis of consciousness can not be adequately understood within the framework of classical physics but must be sought within the alternative picture of physical reality provided by quantum mechanics. The proponents of the quantum consciousness approach regard the radically alternative and often counterintuitive nature of quantum physics as just what is needed to overcome the supposed explanatory obstacles that confront more standard attempts to bridge the psycho-physical gap.

Again there are a wide range of specific theories and models that have been proposed, appealing to a variety of quantum phenomena to explain a diversity of features of consciousness. It would be impossible to catalog them here or even explain in any substantial way the key features of quantum mechanics to which they appeal. However, a brief selective survey may provide a sense, however partial and obscure, of the options that have been proposed.

The physicist Roger Penrose (1989, 1994) and the anesthesiologist Stuart Hameroff (1998) have championed a model according to which consciousness arises through quantum effects occurring within subcellular structures internal to neurons known as microtubules. The model posits so called “objective collapses” which involve the quantum system moving from a superposition of multiple possible states to a single definite state, but without the intervention of an observer or measurement as in most quantum mechanical models. According to the Penrose and Hameroff, the environment internal to the microtubules is especially suitable for such objective collapses, and the resulting self-collapses produce a coherent flow regulating neuronal activity and making non-algorithmic mental processes possible.

The psychiatrist Ian Marshall has offered a model that aims to explain the coherent unity of consciousness by appeal to the production within the brain of a physical state akin to that of a Bose-Einstein condensate. The latter is a quantum phenomenon in which a collection of atoms acts as a single coherent entity and the distinction between discrete atoms is lost. While brain states are not literally examples of Bose-Einstein condensates, reasons have been offered to show why brains are likely to give rise to states that are capable of exhibiting a similar coherence (Marshall and Zohar 1990).

A basis for consciousness has also been sought in the holistic nature of quantum mechanics and the phenomenon of entanglement, according to which particles that have interacted continue to have their natures depend upon each other even after their separation. Unsurprisingly these models have been targeted especially at explaining the coherence of consciousness, but they have also been invoked as a more general challenge to the atomistic conception of traditional physics according to which the properties of wholes are to be explained by appeal to the properties of their parts plus their mode of combination, a method of explanation that might be regarded as unsuccessful to date in explaining consciousness (Silberstein 1998, 2001).

Others have taken quantum mechanics to indicate that consciousness is an absolutely fundamental property of physical reality, one that needs to be brought in at the very most basic level (Stapp 1993). They have appealed especially to the role of the observer in the collapse of the wave function, i.e., the collapse of quantum reality from a superposition of possible states to a single definite state when a measurement is made. Such models may or may not embrace a form of quasi-idealism, in which the very existence of physical reality depends upon its being consciously observed.

There are many other quantum models of consciousness to be found in the literature—some advocating a radically revisionist metaphysics and others not—but these four provide a reasonable, though partial, sample of the alternatives.

9.9 Non-physical theories

Most specific theories of consciousness—whether cognitive, neural or quantum mechanical—aim to explain or model consciousness as a natural feature of the physical world. However, those who reject a physicalist ontology of consciousness must find ways of modeling it as a nonphysical aspect of reality. Thus those who adopt a dualist or anti-physicalist metaphysical view must in the end provide specific models of consciousness different from the five types above. Both substance dualists and property dualists must develop the details of their theories in ways that articulate the specific natures of the relevant non-physical features of reality with which they equate consciousness or to which they appeal in order to explain it.

A variety of such models have been proposed including the following. David Chalmers (1996) has offered an admittedly speculative version of panpsychism which appeals to the notion of information not only to explain psycho-physical invariances between phenomenal and physically realized information spaces but also to possibly explain the ontology of the physical as itself derived from the informational (a version of “it from bit” theory). In a somewhat similar vein, Gregg Rosenberg has (2004) proposed an account of consciousness that simultaneously addresses the ultimate categorical basis of causal relations. In both the causal case and the conscious case, Rosenberg argues the relational-functional facts must ultimately depend upon a categorical non-relational base, and he offers a model according to which causal relations and qualitative phenomenal facts both depend upon the same base. Also, as noted just above (section 9.8), some quantum theories treat consciousness as a fundamental feature of reality (Stapp 1993), and insofar as they do so, they might be plausibly classified as non-physical theories as well.

10. Conclusion

A comprehensive understanding of consciousness will likely require theories of many types. One might usefully and without contradiction accept a diversity of models that each in their own way aim respectively to explain the physical, neural, cognitive, functional, representational and higher-order aspects of consciousness. There is unlikely to be any single theoretical perspective that suffices for explaining all the features of consciousness that we wish to understand. Thus a synthetic and pluralistic approach may provide the best road to future progress.

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consciousness: and intentionality | consciousness: higher-order theories | consciousness: representational theories of | consciousness: unity of | dualism | epiphenomenalism | free will | functionalism | materialism: eliminative | panpsychism | qualia | qualia: knowledge argument | quantum theory: and consciousness | self-knowledge | universals: the medieval problem of | zombies

Acknowledgments

The SEP editors would like to thank Claudio Vanin for pointing out a rather lengthy list of typographical errors that had crept into this entry. We're grateful to him for taking the time to compile the list.


Links  

https://en.wikipedia.org/wiki/Category:Consciousness

https://en.wikiversity.org/wiki/Category:Consciousness

Consciousness is the quality or state of being aware of an external object or something within oneself. It has been defined as: subjectivity, awareness, sentience, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind. Despite the difficulty in definition, many philosophers believe that there is a broadly shared underlying intuition about what consciousness is.

Subcategories

`0-9`A

`B

`C

` ► Cognition (27 C, 224 P)

► Coma (16 P)

`D

` ► Devices to alter consciousness (2 C, 19 P, 3 F)

`E

`F

` ► Fiction about consciousness transfer (1 C, 4 P)

`G`H

`I

Consciousness vs Intelligence

`J`K

`L

`M

`N

`O

`P

`Q

` ► Qualia (5 C, 8 P)

`R

`S

► Subjective experience (8 C, 24 P)

`T

`U

` ► Unconscious (1 C, 8 P)

`V

`W

` ► Works about consciousness (2 C, 1 P)

`X`Y`Z

`

Index

```[[[ёёё

Consciousness, Awareness and the Mind

`A

` Activation-synthesis hypothesis

Altered level of consciousness

Animal consciousness

Anti-nesting principle

Artificial consciousness

Awareness

`C

` Chaitanya (consciousness)

Choiceless awareness

Class consciousness

Collective Consciousness

Communalness

Consciousness after death

Consciousness and the Brain

Consciousness Industry

`D

` Disorders of consciousness

Divided consciousness

Dual consciousness (neuroscience)

`E

` Enactivism

Enchanted loom

Experience

Extended mind thesis

`F

` Functional approach

`G

Global Consciousness

`H

` Higher-order theories of consciousness

`I

` Introspection

`L

` Legal consciousness

`M

No Mental Processes at Full Consciousness

` Mental substance

`N

` Naivety

`O

` Online Consciousness Conference

`P

` Persistent vegetative state

Planetary consciousness

Primary Consciousness

`S

Secondary Consciousness

Self-Awareness

Self-consciousness

Self-consciousness (Vedanta)

Self-discovery

Self-Reflection

Subject (philosophy)

Svasaṃvedana

`T

` Ivan Tyrrell

`V

` Von Neumann–Wigner interpretation

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Categories:

Neuropsychological assessment

Phenomenology

Emergence

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