
For more information on consciousness, visit Britannica.com.
The twentieth-century British psychologist Stuart Sutherland once defined consciousness as ‘a fascinating but elusive phenomenon: it is impossible to specify what it is, what it does, or why it evolved. Nothing worth reading has been written about it.’ Consciousness is indeed hard to define, but most people have an intuitive idea of what it is. It encompasses two different concepts: the notion of a self, and the feelings of which the self is aware, especially qualia — our raw sensory experiences.
Although some philosophers (panpsychists) have believed that all things, including inanimate objects such as chairs and umbrellas, are conscious, most people agree that consciousness is associated with brains (and, some would argue, with inanimate machines that work, in some crucial respect, like brains). Stated simply, then, the problem is how does the activity of nerve cells in the brain give rise to our subjective mental life? Neurons — specks of jelly in the brain, with their electrical impulses and their little squirts of neurotransmitter — seem so utterly different from the redness of red or the flavour of Marmite on toast.
The riddle of qualia is best illustrated with a thought experiment. Imagine a neuroscientist in some future century, who has complete knowledge of the workings of the brain — including the mechanisms of colour vision — but who happens to be colour blind and cannot herself distinguish between red and green. She uses the latest scanning techniques to generate a total description of all the electrical and chemical events in the brain of a normal human as he looks at a red object. The functional account may seem complete, but how could it be so without an explanation of the nature of the unique experience of red, which the scientist herself has never had? There is a deep epistemological gulf between descriptions of physical events in the brain and the personal, subjective experiences that we presume to be associated with those events.
Is consciousness a property of the entire brain — does it ‘emerge’ when the brain reaches a certain level of complexity? Or are only some parts of the brain conscious? (After all, if we argue that only brains and not other organs are conscious, why not imagine that only some parts of the brain are involved?) Indeed, neurological evidence suggests that we are unconscious of most of the activity in our brains — not just the below-stairs business of running the heart, digestion, posture, and so on, but also the pre-perceptual processing of information from the senses, and the complex task of selecting and controlling the individual muscles that carry out actions.
A rare disorder, aptly called ‘blindsight’, strikingly demonstrates a dissociation between conscious and unconscious visual processing. It results from damage restricted to the primary visual cortex in the cerebral hemispheres, which classically causes ‘cortical blindness’ in a corresponding part of the visual field. Although the patient denies seeing, say, a small spot of light presented in the blind part of the field, he or she can fairly accurately point towards the spot. Moreover, if a moving spot or a line is shown, the patient can ‘guess’ the direction of movement or the angle of the line, all the time unaware that it exists! This amazing paradox is explained by the fact that there are two main pathways of interconnected nerve cells from the eyes and through the brain. One goes to the primary visual cortex, and on into the lower parts of the temporal lobe, which is responsible for the identification of objects and the laying down of personal memories. The other projects via the reflex visual centres of the midbrain (which control eye movements) and thence up to the parietal lobes of the cortex, where the information is used to guide hand movements. Since the latter pathway is still intact in the patient with blindsight, he or she can use it for reaching for the object. But the other pathway into the temporal lobe seems to be intimately involved in conscious perception. A more subtle dissociation can occur in patients who have extensive damage to the temporal lobe, which does not interfere with basic visual functions but can cause agnosia — an incapacity to distinguish consciously between different objects and shapes. However, such patients can correctly shape their hands to pick up different objects that they cannot perceptually distinguish. It is almost as though there is an unconscious ‘zombie’ inside the heads of such patients, ‘seeing’ the world and guiding the hands but not troubling consciousness with what it is doing.
Unconscious vision is not just a neurological anomaly — it occurs even in normal people. If you are driving a car while talking to the person next to you or on a mobile telephone, many parts of your brain are processing enormous amounts of visual information to enable you to negotiate the traffic. Yet little of it reaches consciousness so long as your attention is focused on the conversation. Interestingly, it is hard to imagine the opposite scenario — of having a conversation unconsciously while paying attention to the traffic. At any instant, we seem to be fully aware of only a minute fraction of the things that we could be aware of. As you stand chatting to a friend at a party, you are unaware of the content of the other conversations around you — unless you deliberately eavesdrop out of the ‘corner of your ear’. Equally, our embarrassingly poor ability to recall the detail of a visual scene if the lights are suddenly switched off indicates that we are genuinely aware of only a tiny fraction of the flood of information that pours into our brains from our eyes. Only the focus of current attention seems fully represented in our consciousness, in the sense that it can be remembered. This all suggests that there is a link between consciousness, attention, and memory, and also that we cannot use language creatively without being conscious.
This raises the so-called ‘Zombie problem’. If we are able to do so much without being aware of it, what purpose does consciousness serve, and how did it evolve? Imagine an unconscious zombie that looks exactly like a person and does all the things a conscious human does, but without being conscious. There seems to be nothing logically impossible about this. Indeed, we have no way of knowing, for sure, that machines, animals, or even other human beings are truly conscious in the way that we feel ourselves to be. Some philosophers, most notably Gilbert Ryle, have argued that concepts of mind, such as self and intention, are merely ‘category mistakes’ — muddles that arise from the misuse of language. Such virtuosic philosophical argument reinforces the ‘Zombie problem’, but is deeply unsatisfactory. We know that we are conscious. Indeed, as René Déscartes pointed out, knowing that we are aware is the only thing that we are really sure about — ‘cogito, ergo sum’.
In parallel with Ryle's attempt to explain away the ‘Ghost in the Machine’, the school of psychology called behaviourism also argued that consciousness does not (or need not) exist and that science should confine itself to an attempt to explain externally observable behaviour. To behavioural psychologists, it has indeed been valuable to view the brain objectively, merely seeking accounts of behaviour without the baggage of common-language concepts such as will, intention, and need. However, it is difficult for most people — even brain researchers — to accept the extreme notion of ‘eliminative materialism’, namely that words such as ‘love’, ‘want’, and even ‘red’ have the same logical status as the once universal but now arcane view that living things have some kind of ‘vital essence’, which distinguishes them from the inanimate world.
More intriguing is epiphenomenalism. Just as the shadow of a running horse appears to run along with it but plays no causal role in the running, consciousness may simply accompany certain brain events but not itself have a function. Can it really be true that when you feel that you are choosing to pick up a cup, it is not the conscious intention that initiates the picking up? In fact, there is growing evidence that our subjective impressions of events in the world and of our intended actions are a kind of post-hoc ‘commentary’ on things that have already happened. Disturbing though it is, our conscious lives may be a plausible but illusory tale, a translation of the zombie world into the domain of subjectivity. But why should we have such a self-deluding system in the brain? How did it evolve? What could its value be?
Faced with such philosphical conundrums, many neuroscientists, with Francis Crick as their standard-bearer, have argued that we should simply aim to define the ‘neural correlate of consciousness’ — the parts of the brain and the nature and activity of nerve cells that implement conscious states. Once we have a clear understanding of the neural activity that is both necessary and sufficient for subjectivity, perhaps many of the philosophic problems will disappear.
The pragmatic advantage of this approach is that it transforms consciousness into an empirical problem that is approachable experimentally. Instead of asking ‘What is consciousness?’, one asks ‘What parts of the brain are active, or in what special way are they active, when someone does something consciously?’ One experimental approach that is proving fruitful is to monitor the activity of different parts of the cerebral cortex (with microelectrodes in animals, or with imaging techniques in human beings) while the retinal image is unchanging but the content of consciousness changes. For instance, how does activity in the brain change as a person or animal shifts attention from one thing to another? What happens when they view ambiguous visual images that can appear, at one moment, to be one thing, but, at another instant, to be something else?
That other mysterious aspect of subjectivity — the feeling of ‘free will’ and intention — is more difficult to study. However, fingers of evidence point towards the anterior cingulate cortex, a region on the inner surface of the frontal lobe. Patients with damage here sometimes feel that their own actions occur without being intended — alien hand syndrome. Conversely, they may be fully conscious but feel that they don't want to do anything at all — akinetic mutism.
The early decades of the twenty-first century will undoubtedly see great advances in our understanding of the neural correlate of consciousness. What is less certain is whether such empirical observations will take us any closer to resolving what philosopher David Chalmers has called the ‘Hard Problem’, that is, what really is the nature of subjectivity? We may be forced to admit that consciousness, like infinity and the particle-wave concepts in quantum mechanics, is a property that cannot be made intuitively straighforward. Consciousness, like gravity, mass, and charge, may be one of the irreducible properties of the universe for which no further account is possible.
— V. S. Ramachandran, Colin Blakemore
Bibliography
See also brain; colour blindness; illusions; imaging techniques; perception; vision.
noun
Definition: knowledge
Antonyms: senselessness, stupidity, unconsciousness
Possibly the most challenging and pervasive source of problems in the whole of philosophy. Our own consciousness seems to be the most basic fact confronting us, yet it is almost impossible to say what consciousness is. Is mine like yours? Is ours like that of animals? Might machines come to have consciousness? Is it possible for there to be disembodied consciousness? Whatever complex biological and neural processes go on backstage, it is my consciousness that provides the theatre where my experiences and thoughts have their existence, where my desires are felt and where my intentions are formed. But then how am I to conceive the ‘I’, or self that is the spectator, or at any rate the owner of this theatre? These problems together make up what is sometimes called ‘the hard problem’ of consciousness. One of the difficulties in thinking about consciousness is that the problems seem not to be scientific ones; Leibniz remarked that if we could construct a machine that could think and feel, and blow it up to the size of a mill and thus be able to examine its working parts as thoroughly as we pleased, we would still not find consciousness (Monadology, para. 17), and drew the conclusion that consciousness resides in simple subjects, not complex ones. Even if we are convinced that consciousness somehow emerges from the complexity of brain functioning, we may still feel baffled about the way the emergence takes place, or why it takes place in just the way it does.
The nature of conscious experience has been the largest single obstacle to physicalism, behaviourism, and functionalism in the philosophy of mind: these are all views that according to their opponents, can only be believed by feigning permanent anaesthesia. But many philosophers are convinced that we can divide and conquer: we may make progress not by thinking of one ‘hard’ problem, but by breaking the subject up into different skills and recognizing that rather than a single self or observer we would do better to think of a relatively undirected whirl of cerebral activity, with no inner theatre, no inner lights, and above all no inner spectator.
1. The condition of a person who is awake, rather than asleep, so that he or she is able to respond to stimuli.
2. Clinically, different levels of behaviour that can be described on a continuum from a high state of consciousness (alertness and great awareness) to a depressed state of consciousness (coma).
3. The mechanism or process by which humans are aware of sensations, elements in memory, or internal events.
Bibliography
See D. C. Dennett, Consciousness Explained (1991); A. Damasto, The Feeling of What Happens (1999); S. Blackmore, Consciousness: A Very Short Introduction (2005); C. S. Hill, Consciousness (2009); D. J. Chalmers, The Character of Consciousness (2010).
In psychology, consciousness is the subject's immediate apprehension of mental activity. Although Freud thought that conscious processes are "the same as the consciousness of the philosophers and of everyday opinion" and "a fact without parallel, which defies all explanation or description" (1940a [1938], pp. 159, 157), he argued that they could not be considered the "essence" of mental life. Rather, consciousness has a fugitive quality and does not "form unbroken sequences which are complete in themselves" (p. 157). "The psychical, whatever its nature may be, is in itself unconscious and probably similar in kind to all the other natural processes of which we have obtained knowledge" (1940b [1938], p. 283). Freud stressed, however, that consciousness still plays an importance role; indeed, it is "the one light which illuminates our path and leads us through the darkness of mental life" (p. 286).
The work of psychoanalysis, as Freud saw it, is "translating unconscious processes into conscious ones, and thus filling in the gaps in conscious perception" (p. 286). Consciousness is the qualitative perception of information arising both from the external world and from the internal world: an external world that is unknowable in itself and to which we have access only via subjective elements collected by our sense organs and an internal world that consists of unconscious mental processes and that we are aware of solely through sensations of pleasure/unpleasure and revived memories. According to Freud, "A person's own body, and above all its surface, is a place from which both external and internal perceptions may spring" (1923b, p. 25).
From the beginning Freud treated consciousness and perception as indissolubly linked, indeed, so much so that throughout his work he deemed them to constitute a single structure, the perception-consciousness system. Freud also drew a distinction, within nonconscious phenomena, between latent states susceptible of becoming conscious at any moment and repressed psychic processes inaccessible to consciousness. This led him to differentiate the unconscious system proper from a preconscious system, cut off from consciousness by censorship but also controlling access to consciousness. In this sense, the preconscious and the conscious are very close: both are governed by secondary processes and both draw on a bound form of psychic energy. In The Interpretation of Dreams (1900a), Freud spoke of the preconscious-conscious system, and in "The Unconscious" (1915e), he described the preconscious as "conscious knowledge" (p. 167), even though it provides access to unconscious contents and processes, provided that they have been transformed.
From his earliest writings on, Freud saw the link between consciousness and the ego as very close. And although by 1920 Freud viewed the ego as in large part unconscious in its defensive activities, he continued to attach consciousness to it as both the "nucleus" and the "surface of the mental apparatus" (1923b, p. 19).
By the early twenty-first century, the problem of perception had become increasingly complex. Freud's near conflation of perception and consciousness, which required him to postulate that perceptual phenomena and the laying down of memory traces are incompatible, has come in for serious reconsideration. It is worth noting, though, that Freud himself, in his last years, was given pause on this issue by the problem of fetishism, apropos of which it was apparent that perceptions and mnemic traces could be caught up in one and the same conflict. This line of thinking has led to a reevaluation of all psychopathologies where disavowal and splitting predominate, such as borderline conditions, and more generally, to a review of all states involving the relationship between perception and hallucination (see Donald W. Winnicott's notions of the subjective object and of transitionality [1953]).
Bibliography
Freud, Sigmund. (1900a). The interpretation of dreams. SE, 4-5.
——. (1915e). The unconscious. SE, 14: 166-204.
——. (1923b). The ego and the id. SE, 19: 12-59.
——. (1940a [1938]). An outline of psychoanalysis. SE, 23: 139-207.
——. (1940b [1938]). Some elementary lessons in psycho-analysis. SE, 23: 279-286.
Winnicott, Donald W. (1953). Transitional objects and transitional phenomena: A study of the first not-me possession. International Journal of Psycho-Analysis, 34, 89-97.
—RAYMOND CAHN
Michael A. Arbib
Even 'simple' mammals may be aware of the difference between feeling maternal and feeling enraged. Such 'animal awareness' seems to be part of human consciousness but the latter seems qualitatively different in nature. I argue that we are conscious in a fully human sense only because we have language. However, I deny that consciousness is merely a function of language. For example, one may have a vivid, conscious perception of a face yet be unable to put it into words. The argument of this article is further developed in Arbib (2001).Susan Blackmore
Whenever we ask 'Am I conscious now?' the answer seems to be 'Yes'. We always seem to be consciously feeling, hearing, and seeing something. But how can the existence of millions of interconnected brain cells give rise to this personal, private, ineffable experience? Either we must answer this question, or show why it is the wrong question.Ned Block
There are two broad classes of empirical theories of consciousness, which I will call the biological and the functional. The biological approach is based on empirical correlations between experience and the brain. For example, there is a great deal of evidence that the neural correlate of visual experience is activity in a set of occipitotemporal pathways, with special emphasis on the inferotemporal cortex.David Chalmers
The conscious life of a subject comprises all sorts of subjective experiences: visual experiences, other sensory experiences, bodily sensations, mental imagery, and a stream of occurrent thought. There is something it is like to have these experiences, from the subject's point of view. The hard problem of consciousness is that of explaining how it is that physical processes in a brain are associated with experiences of this sort.Paul M. Churchland
This ill-defined topic, which has yet to find a governing research paradigm, is perhaps best defined by a series of unanswered questions. What distinguishes our waking state from such diverse states as deep sleep, trauma-induced coma, and the unconscious state induced by anaesthetics? Also, what distinguishes the brain's conscious representations and activities from the vast majority of its representational and computational activities that never ascend to that special status? Further, what structural, representational, or dynamical features of the brain are responsible for the emergence of conscious activity? And finally, what special functions does it perform that made conscious brains worthy of natural selection in the first place?Dan Dennett
Consciousness often seems to be utterly mysterious. I suspect that the principal cause of this bafflement is a sort of accounting error that is engendered by a familiar series of challenges and responses. A simplified version of one such path to mysteryland runs as follows:Ian Glynn
So far as we can tell, consciousness is always associated with nervous activity in a complex brain, and it is clear that interference with such activity — by changes in sensory input, or injury, or disease, or drugs, or direct electrical stimulation — can alter conscious states. It therefore seems likely that individual conscious states can exist only in the presence of particular patterns of nervous activity, and that the existence of these patterns is always associated with the corresponding conscious states. It is such patterns that are referred to as the neural correlates of consciousness. Why certain patterns of nervous activity should be always associated with certain thoughts or feelings is, of course, among the most difficult of all problems, but determining what these patterns are would seem to be a necessary first step — though only a first step — towards solving it.Richard L. Gregory
1. Flagging the present
One can imagine a bunch of interacting robots getting on fine without any awareness, or qualia, but surely they would not spend hours looking at pictures or listening to Beethoven. This is just how, only a few decades ago, behaviourist psychologists described us — as lacking qualia of red or pain, or the sound of violins. Why audiences without music qualia would sit through a symphony was hardly questioned. Psychology has now abandoned the behaviourism of J. B. Watson and B. F. Skinner, who tried to make psychology seem more scientific and less whimsical by denying consciousness, though at the cost of throwing out the baby with the bathwater. The situation is indeed reversed, as physicists, especially Roger Penrose, are now asking how the physical world can have consciousness.2. Exceptional cases
This is not infallible. At least one person with exceptionally vivid memories has been described who confused memories with present reality. This is the remarkable case of Mr S, described by the Russian neuropsychologist Alexander Luria. Mr S was a professional memory man, with incredibly vast memory and extremely vivid imagination. But he confused his vivid memories with real-time reality, to the point of danger. He would confuse imagined with real traffic lights. And, as he said, 'I'd look at a clock and for a long while continue to see the hands fixed just as they were, and not realize time had passed ... That's why I'm often late.'Nicholas Humphrey
Fashions change. The problem of consciousness, once banned from serious consideration by psychologists, is again high on the agenda. Yet typically researchers are looking under the lamp that currently shines brightest rather than in the area where the phenomenon went missing. They are identifying consciousness with high-level thought processes and seeking to explain it in 'thinking machine' terms, but they are largely ignoring bodily feeling.David Papineau
To many it seems obvious that the conscious mind must be distinct from the physical brain. How could mere neural activity possibly constitute the vibrant subjective world of colour experience, pain, and emotion?Roger Penrose
Most scientific discussions concerning the nature of consciousness attempt to find an explanation for this phenomenon in terms of the physical picture of the world that is known today. Particularly popular is computational functionalism (or strong AI), which asserts that it is entirely the computational action of the pattern of neuron firings and synaptic responses that is responsible for our awareness, our feelings of free will, and other aspects of consciousness. Some neurophysiologists argue that the computational model is inadequate and that the detailed neurochemistry of the brain must play an essential role in determining consciousness. Still others would claim that the physics of quantum theory is a key ingredient, and that free will is dependent on quantum indeterminism.Brian Pippard
Nineteenth-century scientists, in their work as in their daily lives, took for granted the reality of the world around them and sought to account for it at every level by the Newtonian mechanics which, on the human scale, appeared both reasonable and flawless. The forces of gravitation and electromagnetism demanded a medium, the aether — intangible but still Newtonian — by which they could operate across apparently empty space. Failure to invent a plausible model, the advent of Einstein's relativity, and finally quantum mechanics demolished this ideal programme. Action-at-a-distance was restored to the status of an unexplained mathematical rule, as Newton had been forced to leave it, and a succession of new fundamental particles had to be accepted even if their behaviour defied visualization. No longer could we conceive of a definite path connecting one event with the next; indeterminacy was an inevitable consequence of Schrödinger's equation, which gave the right answer to a vast range of problems. Despite many ingenious attempts, which are still being made, no consistent substitute has been found for the early Copenhagen doctrine that limits the scientist's business to the precise description and correlation of observations shared by competent investigators. Ultimate reality, whatever it may be, is a matter for metaphysicians, not scientists.Steven Rose
A few years ago I was at a conference at which a bright young Harvard neurophysiologist referred to the study of consciousness as a 'CLM' — a career-limiting move. Today however I fear that the way most neuroscientists approach the matter is itself a CLM — a consciousness-limiting move. The term consciousness has multiple rich meanings. Social and political sciences deal with such concepts as class, race, and gender consciousness. Philosophers may ponder the etymological relationship between consciousness and conscience. Psychoanalysts will contrast consciousness and 'the unconscious', by which they definitely do not mean what an anaesthetist or neurologist might imply. All these rich, social, historical, and personal developmental meanings are lost in the discourse of most neuroscientists. For them, being conscious is merely the antithesis of being asleep or unconscious in the anaesthetist's sense. Thus consciousness reduces to mere 'awareness' and the discussion then focuses on how the multitude of sense data impinging on our brains at any moment becomes ordered and refined into that most relevant for our immediate needs. Francis Crick in his book The Astonishing Hypothesis puts this most clearly, following with a further reductionist move: on the basis that more is known about the neurobiology of the visual system than that of any other sensory process, he proposes to exploit the neural mechanisms of perception as a model system, tractable to experiment (and ends the book with an aside locating free will in the anterior cingulate!).
Quotes:
"But they for whom I am the supreme goal, who do all work renouncing self for me and meditate on me with single-hearted devotion, these I will swiftly rescue from death's vast sea, for their consciousness has entered into me."
- Bhagavad Gita
"The real history of consciousness starts with one's first lie."
- Joseph Brodsky
"It is our less conscious thoughts and our less conscious actions which mainly mould our lives and the lives of those who spring from us."
- Samuel Butler
"The unconscious is the ocean of the unsayable, of what has been expelled from the land of language, removed as a result of ancient prohibitions."
- Italo Calvino
"A sub-clerk in the post-office is the equal of a conqueror if consciousness is common to them."
- Albert Camus
"Consciousness is much more than the thorn, it is the dagger in the flesh."
- E. M. Cioran
See more famous quotes about Consciousness
The state of being conscious; responsiveness of the brain to impressions made by the senses. Altered states range from the normal, complete alertness to depression, confusion, delirium and finally loss of consciousness.
A state in which the individual is capable of rational response to questioning and has all protective reflexes intact, including the ability to maintain a patent airway.

Consciousness is a term that refers to the relationship between the mind and the world with which it interacts.[1] It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind.[2] Despite the difficulty in definition, many philosophers believe that there is a broadly shared underlying intuition about what consciousness is.[3] As Max Velmans and Susan Schneider wrote in The Blackwell Companion to Consciousness: "Anything that we are aware of at a given moment forms part of our consciousness, making conscious experience at once the most familiar and most mysterious aspect of our lives."[4]
Philosophers since the time of Descartes and Locke have struggled to comprehend the nature of consciousness and pin down its essential properties. Issues of concern in the philosophy of consciousness include whether the concept is fundamentally valid; whether consciousness can ever be explained mechanistically; whether non-human consciousness exists and if so how it can be recognized; how consciousness relates to language; and whether it may ever be possible for computers or robots to be conscious. Perhaps the thorniest issue is whether consciousness can be understood in a way that does not require a dualistic distinction between mental and physical states or properties.
In recent years, consciousness has become a significant topic of research in psychology 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 by asking human 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 psychoactive 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.[5] 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.[6]
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The origin of the modern concept of consciousness is often attributed to John Locke's Essay Concerning Human Understanding, published in 1690.[7] Locke defined consciousness as "the perception of what passes in a man's own mind."[8] His essay influenced the 18th century view of consciousness, and his definition appeared in Samuel Johnson's celebrated Dictionary (1755).[9]
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" + scire "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.[10] 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."[11] 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".[12] 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.[13] Here, conscientia is the knowledge that a witness has of the deed of someone else.[14] 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.[15] Descartes used "conscientia" the way modern speakers would use "conscience." In Search after Truth he says "conscience or internal testimony" (conscientia vel interno testimonio).[16]
The philosophy of mind has given rise to many stances regarding consciousness. Any attempt to impose an organization on them is bound to be somewhat arbitrary. Stuart Sutherland exemplified the difficulty in the entry he wrote 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.[17]
Most writers on the philosophy of consciousness have been concerned to defend 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. The main alternative, followed in the present article, is to organize philosophical stances according to the answers they give to a set of basic questions about the nature and status of consciousness.
The most compelling argument for the existence of consciousness is that the vast majority of mankind have an overwhelming intuition that there truly is such a thing.[18] Skeptics argue that this intuition, in spite of its compelling quality, 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.[19] More generally, many philosophers and scientists have been unhappy about the difficulty of producing a definition that does not involve circularity or fuzziness.[17]
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.[20] 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, or else is an umbrella term encompassing a variety of distinct meanings with no simple element in common.[21]
Ned Block proposed a distinction between two types of consciousness that he called phenomenal (P-consciousness) and access (A-consciousness).[22] 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,[23] 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.[24]
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.[25]
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).[26] He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the pineal gland.[27]
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.[28] Alternative solutions, however, have been very diverse. They can be divided broadly into two categories: dualist solutions that maintain Descartes's 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 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 camps.[29]
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.[30] The most influential modern physical theories of consciousness are based on psychology and neuroscience. Theories proposed by neuroscientists such as Gerald Edelman[31] and Antonio Damasio,[32] and by philosophers such as Daniel Dennett,[33] seek to explain consciousness in terms of neural events occurring within the brain. Many other neuroscientists, such as Christof Koch,[34] 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.[35]
A few theoretical physicists have argued that classical physics is intrinsically incapable of explaining the holistic aspects of consciousness, but that quantum theory provides the missing ingredients. Several theorists have therefore proposed quantum mind (QM) theories of consciousness.[36] 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 has been confirmed by experiment. Recent papers by Guerreshi, G., Cia, J., Popescu, S. and Briegel, H.[37] could falsify proposals such 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.[38]
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?[39] This is called the problem of other minds.[40] 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.[41]
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.[42] 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.[42] 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.[43] 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.[44] For further explanation for why people believe other people have consciousness look at Peter Carruthers Phenomenal Consciousness. He goes through explanations about theory of mind and higher order thought. His explanations provide more complex answers through our various mental strategies in theory of mind that lead us to believe we are conscious as well as other people while trees and rocks are not conscious.
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 animals, lacking the ability to express human language, cannot tell us about their experiences.[45] 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.[46] Most people have a strong intuition that some animals, such as dogs, are conscious, while others, such as insects, are not; but the sources of this intuition are not obvious.[45]
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.[47] Other thinkers, such as Douglas Hofstadter, dismiss this argument as incoherent.[48] 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.[49]
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.[50] 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.[51]
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.[52] 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,[53] while David Chalmers argues that a philosophical zombie could pass the test, yet fail to be conscious.[54]
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 gets in a room stocked with algorithms programmed to respond to Chinese questions, i.e., Turing machines, programmed to correctly answer in Chinese questions asked in Chinese, and he finds he's 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. And, this is all a current computer program would do. 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 affectively aware of what was being said and the purposes it might serve: Searle passes the Turing test of answering the questions in both languages, but he's only conscious of what he's doing when he speaks English. Another way of putting the argument is to say computational computer programs can pass the Turing test for processing the syntax of a language, but that semantics cannot be reduced to syntax in the way Strong AI advocates hoped: processing semantics is conscious and intentional because we use semantics to consciously produce meaning by what we say.[55]
In the literature concerning artificial intelligence (AI), Searle's essay has been second only to Turing's in the volume of debate it has generated.[55] 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,[56] 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[57]
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One argument in the field of philosophy of consciousness deals with what it is that makes a mental state “conscious” in the sense of there being something it is like to experience that state. David Rosenthal posits the “transitivity principle” as a possible answer to this question. This principle holds that what makes a state conscious is the individual being aware of being in that state. This happens, on Rosenthal’s account, through the use of a higher-order thought that is directed on the mental state in question.
Rosenthal cites several empirical paradigms in support of his theory. Blind-sight is one. This is a phenomenon that occurs in individuals with damage to the visual center of their brains. These individuals are often capable of relatively simple forms of visual awareness (like being able to spatially locate an x in a picture) but do not report anything it is like to experience these visual stimuli. Rosenthal claims that this can only be explained as a perception which the subject is not aware of experiencing.
Rosenthal also cites masked-priming, in which the individual is presented a priming stimulus which is quickly replaced by a masking stimulus. The individual does not report having experienced the state even though they clearly received the visual input. Again, Rosenthal claims that this can only be an instance of a visual stimulus of which the subject is not aware, and which there is therefore nothing it is like to experience.
Fred Dretske has objected to the transitivity principle on the basis that we often experience mental states that are consciously different without being aware of the conscious different. For instance, one might look at a picture of two forests. The pictures might be exactly the same except that there is one tree that is present in one picture but absent in the other. Dretske points out that what it is like to see the one forest is different from what it is like to see the other. And yet the individual looking at the pictures can easily fail to be aware that they differ at all.
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. Krishna consciousness, for example, is a term used to mean an intimate linkage between the mind of a worshipper and the god Krishna.[58] 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.[59] Many more examples could be given. 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.[60]
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.[61] 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.[62] 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,[63] journals such as Consciousness and Cognition, and methodological work published in journals such as the Journal of Consciousness Studies, along with regular conferences organized by groups such as the Association for the Scientific Study of Consciousness.[64]
Modern scientific 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.[34]
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 that is 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.[65] 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.[66] 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.[67]
Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues.[68] 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.[69] 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.[70] 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.[71]
Although verbal report is in practice the "gold standard" for ascribing consciousness, it is not the only possible criterion.[68] 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.[72] 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.[67] 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.[73]
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.[74] Humans (older than 18 months) and other great apes, bottlenose dolphins, pigeons, and elephants have all been observed to pass this test.[75]
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, 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.[76]
One 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.[77] 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 temporal coincidence.[78]
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.[79] 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.[80] 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).[81]
In 2011 Graziano and Kastner[82] proposed the “attention schema” theory of awareness. In that theory specific cortical machinery, notably in the superior temporal sulcus and the temporo-parietal junction, is 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 this cortical machinery can lead to deficits in consciousness such as hemispatial neglect. In the attention schema theory, the value of constructing 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 state. To be aware of X is to construct a model of one’s attentional focus on X.
"The evolution of the capacity to simulate seems to have culminated in subjective consciousness. Why this should have happened is, to me, the most profound mystery facing modern biology" Richard Dawkins, The Selfish Gene. Since 1976, it has remained so.
In 2004, eight neuroscientists felt it was too soon for a definition. They wrote an apology in "Human Brain Function":[83]
In contrast to philosophical definitions, an operational definition can be tested experimentally, and is useful for current research. A current definition for self awareness, proposed in the 1970s by Gordon Gallup, is known as the mirror test. An operational definition proposed in 2012 [84] states "consciousness is the sum of the electrical discharges occurring throughout the nervous system of a being at any given instant". This operational definition is based on Dennett's theory of the Multiple Drafts Model of Consciousness, arising from the Buddha's pluripotent model of consciousness. What many consider consciousness may simply be the personal awareness of all the neurons delivering messages to the mind, but operational consciousness can include all neuronal activity. Extending this concept to all sentient beings, one can measure a range of consciousness based on how many and how powerfully neurons are actually firing, varying from worms to humans. One can answer the question, is someone asleep less conscious than someone thinking about a difficult problem. Although technology does not exist currently to measure this, it can be estimated by determining oxygen consumption by the brain.
Christof Koch lists the following four definitions of consciousness in his latest book [85], which can be summarized as follows: Consciousness is the inner mental life that we lose each night when we fall into dreamless sleep, consciousness can be measured with the Glasgow Coma Scale that assesses the reactions of patients, an active cortico-thalamic complex is necessary for consciousness in humans, and put philosophically, consciousness is what it is like to feel something.
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.[86] 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.[87] 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 infinitely 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.[88] Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see [88]
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.[89] 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.[90] In his paper "Evolution of consciousness," John Eccles argued that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness.[91] 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.[92] 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.[93] 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.[94][95] 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.[96] 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.
There are some states in which consciousness seems to be abolished, including 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.[97]
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. 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.[98]
A variety of psychoactive drugs have notable effects on consciousness. These range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, or most notably by the class of drugs known as psychedelics.[97] LSD, mescaline, psilocybin, 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 well understood, but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter serotonin play an essential role.[99]
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.[100]
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.[101] 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.[102]
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.[103] 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.[104]
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.[105] 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.[24] 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.[106] Most psychologists and neuroscientists have not accepted these arguments — 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.[107]
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, (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.[108] 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.[109]
Despite the large amount of information available, the most important aspects of perception remain mysterious. A great deal is known about low-level signal processing in sensory systems, but the ways by which sensory systems interact with each other, with "executive" systems in the frontal cortex, and with the language system are very incompletely understood. At a deeper level, there are still basic conceptual issues that remain unresolved.[108] 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.[110] 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".[111]
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.[112]
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.[112] Also, bioethicists may be concerned with the ethical implications of consciousness in medical cases of patients such as Karen Ann Quinlan,[113] while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works.[114]
In medicine, consciousness is examined using a set of procedures known as neuropsychological assessment.[72] 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 "oriented times three" (sometimes denoted "Ox3" on a medical chart), and is usually considered fully conscious.[115]
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 indicating brain death (the lowest defined level of consciousness), 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.[112]
Medical conditions that inhibit consciousness are considered disorders of consciousness.[116] 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.[116][117] Differential diagnosis of these disorders is an active area of biomedical research.[118][119][120] Finally, brain death results in an irreversible disruption of consciousness.[116] 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 behavior. |
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.[121] 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 right 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.[122]
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".[123] A similar concept appears in Buddhist philosophy, expressed by the Sanskrit term Citta-saṃtāna, which is usually translated as mindstream or "mental continuum". In the Buddhist view, though, the "mindstream" is viewed primarily as a source of noise that distracts attention from a changeless underlying reality.[124]
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.[125]
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.[126]
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Dansk (Danish)
n. - bevidsthed, forståelse
idioms:
Nederlands (Dutch)
bewustzijn, besef
Français (French)
n. - conscience, conscience collective, (Méd) connaissance
idioms:
Deutsch (German)
n. - Bewußtsein
idioms:
Ελληνική (Greek)
n. - συνείδηση
idioms:
Italiano (Italian)
coscienza, conoscenza
idioms:
Português (Portuguese)
n. - consciência (f), conhecimento (m)
idioms:
Русский (Russian)
сознание, сознательность
idioms:
Español (Spanish)
n. - conciencia, conocimiento
idioms:
Svenska (Swedish)
n. - medvetande, medvetenhet
中文(简体)(Chinese (Simplified))
意识, 自觉, 知觉
idioms:
中文(繁體)(Chinese (Traditional))
n. - 意識, 自覺, 知覺
idioms:
日本語 (Japanese)
n. - 意識, 気づくこと, 精神
idioms:
العربيه (Arabic)
(الاسم) يقظه, تنبه, وعي
עברית (Hebrew)
n. - תודעה, מודעות, הכרה
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