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Consciousness is the quality or state of being aware of an external object or something within oneself. It has been defined as: sentience, awareness, subjectivity, 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. 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."
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; whether consciousness can be understood in a way that does not require a dualistic distinction between mental and physical states or properties; and whether it may ever be possible for computers or robots to be conscious.
At one time consciousness was viewed with skepticism by many scientists, but in recent years it 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. 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.
"Consciousness" derives from Latin conscientia which primarily means moral conscience. In the literal sense, "conscientia" (or "con scientia") means knowledge-with, that is, shared knowledge. The word first appears in Latin juridic texts by writers such as Cicero. Here, conscientia is the knowledge that a witness has of the deed of someone else. In Christian theology, conscience stands for the moral conscience in which our actions and intentions are registered and which is only fully known to God. Medieval writers such as Thomas Aquinas describe the conscientia as the act by which we apply practical and moral knowledge to our own actions. René Descartes has been said to be the first philosopher to use "conscientia" in a way that does not seem to fit this traditional meaning, and, as a consequence, the translators of his writings in other languages like French and English coined new words in order to denote merely psychological consciousness. These are, for instance, conscience, and Bewusstsein. However, it has also been argued that John Locke was in fact the first one to use the modern meaning of consciousness in his Essay Concerning Human Understanding, although it remains closely intertwined with moral conscience (I may be held morally responsible only for the act of which I am conscious of having achieved; and my personal identity - my self - goes as far as my consciousness extends itself). The modern sense of "consciousness" was therefore first found not in Descartes' work - who sometimes used the word in a modern sense, but did not distinguish it as much as Locke would do -, but in Locke's text. The contemporary sense of the word (consciousness associated to the idea of personal identity, which is assured by the repeated consciousness of oneself) was therefore introduced by Locke; but the word "conscience" itself was coined by Pierre Costes, French translator of Locke. Henceforth, the modern sense first appeared in Locke's works, but the word itself first appeared in the French language. Locke's influence upon the concept can be found in Samuel Johnson's celebrated Dictionary, in which Johnson abstains from offering a definition of "consciousness," choosing instead to simply quote Locke.
- Main article: Philosophy of mind
There are many philosophical stances on consciousness, including: behaviorism, dualism, idealism, functionalism, reflexive monism, phenomenalism, phenomenology and intentionality, physicalism, emergentism, mysticism, personal identity etc.
Phenomenal and access consciousness
Phenomenal consciousness (P-consciousness) is simply experience; it is moving, coloured 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. The hard problem of consciousness was formulated by Chalmers in 1996, dealing with the issue of "how to explain a state of phenomenal consciousness in terms of its neurological basis" (Block 2004).
Access consciousness (A-consciousness) 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 often access conscious; when we introspect, information about our thoughts is access conscious; when we remember, information about the past (e.g., something that we learned) is often access conscious; and so on. Chalmers thinks that access consciousness is less mysterious than phenomenal consciousness, so that it is held to pose one of the easy problems of consciousness. Dennett denies that there is a "hard problem", asserting that the totality of consciousness can be understood in terms of impact on behavior, as studied through heterophenomenology. There have been numerous approaches to the processes that act on conscious experience from instant to instant. Philosophers who have explored this problem include Gerald Edelman, Edmund Husserl and Daniel Dennett. Daniel Dennett (1988) suggests that what people think of as phenomenal consciousness, such as qualia, are judgements and consequent behaviour. He extends this analysis (Dennett, 1996) by arguing that phenomenal consciousness can be explained in terms of access consciousness, denying the existence of qualia, hence denying the existence of a "hard problem."
Events that occur in the mind or brain that are not within phenomenal or access consciousness are known as subconscious events.
The description and location of phenomenal consciousness
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Philosophers have investigated phenomenal consciousness for centuries. René Descartes, who arrived upon the famous dictum 'cogito ergo sum', wrote Meditations on First Philosophy in the seventeenth century, containing extensive descriptions of what it is to be conscious. Descartes described conscious experience as ideas such as imaginings and perceptions laid out in space and time that are viewed from a point, and appearing as a result of some quality (qualia) such as color, smell, and so on; this notion of interchangeability between the terms 'idea' and 'imaginings' can cause confusion among modern readers.
Like Aristotle Descartes defines ideas as extended things, as in this excerpt from his Treatise on Man:
Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H [where the seat of the imagination and the 'common sense' is located]. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.
Thus Descartes does not identify mental ideas or 'qualia' with activity within the sense organs, or even with brain activity, but rather with interaction between body and the 'rational soul', through the mediating 'gland H'. This organ is now known as the pineal gland. Descartes notes that, anatomically, while the human brain consists of two symmetrical hemispheres the pineal gland, which lies close to the brain's centre, is singular. Thus he extrapolated from this that it was the mediator between body and soul.
Other philosophers agreed with Descartes to varying degrees, such as Nicolas Malebranche, Thomas Reid, John Locke, David Hume and Immanuel Kant. Malebranche, for example, agreed with Descartes that the human being was composed of two elements, body and mind, and that conscious experience resided in the latter. He did, however, disagree with Descartes as to the ease with which we might become aware of our mental constitution, stating 'I am not my own light unto myself'. David Hume and Immanuel Kant also differ from Descartes, in that they avoid mentioning a place from which experience is viewed (see "Further reading" below); certainly, few if any modern philosophers have identified the pineal gland as the seat of dualist interaction.
The extension of things in time was considered in more detail by Kant and James. Kant wrote that "only on the presupposition of time can we represent to ourselves a number of things as existing at one and the same time [simultaneously] or at different times [successively]." William James stressed the extension of experience in time and said that time is "the short duration of which we are immediately and incessantly sensible."
When we look around a room or have a dream, things are laid out in space and time and viewed as if from a point. However, when philosophers and scientists consider the location of the form and contents of this phenomenal consciousness, there are fierce disagreements. As an example, Descartes proposed that the contents are brain activity seen by a non-physical place without extension (the Res Cogitans), which, in Meditations on First Philosophy, he identified as the soul. This idea is known as Cartesian Dualism. Another example is found in the work of Thomas Reid who thought the contents of consciousness are the world itself, which becomes conscious experience in some way. This concept is a type of Direct realism. The precise physical substrate of conscious experience in the world, such as photons, quantum fields, etc. is usually not specified.
Other philosophers, such as George Berkeley, have proposed that the contents of consciousness are an aspect of minds and do not necessarily involve matter at all. This is a type of Idealism. Yet others, such as Leibniz, have considered that each point in the universe is endowed with conscious content. This is a form of Panpsychism. Panpsychism is the belief that all matter, including rocks for example, is sentient or conscious. The concept of the things in conscious experience being impressions in the brain is a type of representationalism, and representationalism is a form of indirect realism.
It is sometimes held that consciousness emerges from the complexity of brain processing. The general label 'emergence' applies to new phenomena that emerge from a physical basis without the connection between the two explicitly specified.
Some theorists hold that phenomenal consciousness poses an explanatory gap. Colin McGinn takes the New Mysterianism position that it can't be solved, and Chalmers criticizes purely physical accounts of mental experiences based on the idea that philosophical zombies are logically possible and supports property dualism. But others have proposed speculative scientific theories to explain the explanatory gap, such as Quantum mind, space-time theories of consciousness, reflexive monism, and Electromagnetic theories of consciousness to explain the correspondence between brain activity and experience.
Types of consciousness
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. 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 is an umbrella term encompassing a variety of distinct meanings with no simple element in common.
Ned Block proposed a distinction between two types of consciousness that he called phenomenal (P-consciousness) and access (A-consciousness). 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, 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.
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.
- Main article: Mind–body problem
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). He suggested that the interaction between these two domains occurs inside the brain, perhaps in a small midline structure called the pineal gland.
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. Alternative solutions, however, have been very diverse. They 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 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.
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. The most influential modern physical theories of consciousness are based on psychology and neuroscience. Theories proposed by neuroscientists such as Gerald Edelman and Antonio Damasio, and by philosophers such as Daniel Dennett, seek to explain consciousness in terms of neural events occurring within the brain. Many other neuroscientists, such as Christof Koch, 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.
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. 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. 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.
Apart from the general question of the "hard problem" of consciousness, roughly speaking, the question of how mental experience arises from a physical basis, 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
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? This is called the problem of other minds. 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.
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. 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. 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. 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.
- 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 animals, lacking the ability to express human language, cannot tell us about their experiences. 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. 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.
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. Other thinkers, such as Douglas Hofstadter, dismiss this argument as incoherent. 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.
- 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. 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.
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. 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, while David Chalmers argues that a philosophical zombie could pass the test, yet fail to be conscious.
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.
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. 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, 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
The transitivity principle
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 concerning what 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.
Philosophical criticisms of the concept of consciousness
From the eighteenth to twentieth centuries many philosophers concentrated on relations, processes and thought as the most important aspects of consciousness. These aspects would later become known as "access consciousness" and this focus on relations allowed philosophers such as Marx, Nietzsche and Foucault to claim that individual consciousness was dependent on such factors as social relations, political relations and ideology.
Locke's "forensic" notion of personal identity founded on an individual conscious subject would be criticized in the 19th century by Marx, Nietzsche and Freud following different angles. Martin Heidegger's concept of the Dasein ("Being-there") would also be an attempt to think beyond the conscious subject.
Marx considered that social relations ontologically preceded individual consciousness, and criticized the conception of a conscious subject as an ideological conception on which liberal political thought was founded. Marx in particular criticized the 1789 Declaration of the Rights of Man and of the Citizen, considering that the so-called individual natural rights were ideological fictions camouflaging social inequality in the attribution of those rights. Later, Louis Althusser would criticize the "bourgeois ideology of the subject" through the concept of interpellation ("Hey, you!").
Nietzsche, for his part, once wrote that "they give you free will only to later blame yourself", thus reversing the classical liberal conception of free will in a critical account of the genealogy of consciousness as the effect of guilt and ressentiment, which he described in On the Genealogy of Morals. Hence, Nietzsche was the first one to make the claim that the modern notion of consciousness was indebted to the modern system of penalty, which judged a man according to his "responsibility", that is by the consciousness through which acts can be attributed to an individual subject: "I did this! this is me!". Consciousness is thus related by Nietzsche to the classic philosopheme of recognition which, according to him, defines knowledge.
According to Pierre Klossowski (1969), Nietzsche considered consciousness to be a hypostatization of the body, composed of multiple forces (the "Will to Power"). According to him, the subject was only a "grammatical fiction": we believed in the existence of an individual subject, and therefore of a specific author of each act, insofar as we speak. Therefore, the conscious subject is dependent on the existence of language, a claim which would be generalized by critical discourse analysis (see for example Judith Butler).
Michel Foucault's analysis of the creation of the individual subject through disciplines, in Discipline and Punish (1975), would extend Nietzsche's genealogy of consciousness and personal identity - i.e. individualism - to the change in the juridico-penal system: the emergence of penology and the disciplinization of the individual subject through the creation of a penal system which judged not the acts as it alleged to, but the personal identity of the wrong-doer. In other words, Foucault maintained that, by judging not the acts (the crime), but the person behind those acts (the criminal), the modern penal system was not only following the philosophical definition of consciousness, once again demonstrating the imbrications between ideas and social institutions ("material ideology" as Althusser would call it); it was by itself creating the individual person, categorizing and dividing the masses into a category of poor but honest and law-abiding citizens and another category of "professional criminals" or recidivists.
Gilbert Ryle has argued that traditional understandings of consciousness depend on a Cartesian outlook that divides into mind and body, 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 saying 'consciousness,' we end up misleading ourselves by thinking that there is any sort of thing as consciousness separated from behavioral and linguistic understandings.
The failure to produce a workable definition of consciousness also raises formidable philosophical questions. When Antonio Dimasio defines consciousness as "an organism's awareness of its own self and its surroundings," he hasn't said anything. The words "consciousness," "awareness," and "perception" convey a very passive sense, bringing up images of the homunculus observer. The idea of consciousness also implies a gratuitous distinction between awareness and sensation, as if sensation or thought is something we have to be aware of.
The neurological data shows, however, that experience is a very interactive thing. Our brain massages vast libraries of experience that it draws upon to create a coherent body and a coherent world for us. As in the act of reading a text, our reading of our bodies and the world around us is a very active thing. Maturana and Varela showed that the brain is massively involved with creating worlds of experience for us with meager input from the senses.
Evolutionary biologist Richard Dawkins sums up the interactive view of experience: "In a way, what sense organs do is assist our brains to construct a useful model and it is this model that we move around in. It is a kind of virtual reality simulation of the world."
Consciousness and language
Because humans express their conscious states using language, it is tempting to equate language abilities and consciousness. There are, however, speechless humans (infants, feral children, aphasics, severe forms of autism), to whom consciousness is attributed despite language lost or not yet acquired. Moreover, the study of brain states of non-linguistic primates, in particular the macaques, has been used extensively by scientists and philosophers in their quest for the neural correlates of the contents of consciousness.
Julian Jaynes argued to the contrary, in The Origin of Consciousness in the Breakdown of the Bicameral Mind, that for consciousness to arise in a person, language needs to have reached a fairly high level of complexity. According to Jaynes, human consciousness emerged as recently as 1300 BCE or thereabouts. Many philosophers, including W.V. Quine and neuroscientists, including Christof Koch, contest this hypothesis, as it suggests that prior to this "discovery" of consciousness, experience simply did not exist. Ned Block argued that Jaynes had confused consciousness with the concept of consciousness, the latter being what was discovered between the Iliad and the Odyssey. Daniel Dennett argues that consciousness is like money in that having the thing requires having the concept of it, so it is a revolutionary proposal and not a ridiculous error to suppose that consciousness only emerges when its concept does.
Consciousness and Brain Evolution
Other accounts of the origin of consciousness as a brain function approach it as an adaptation, a trait that must in some fashion increase biological fitness.  Sir John C. Eccles considers the problem in his paper "Evolution of consciousness." He argues that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness.  Budiansky, by contrast, limits consciousness to humans, proposing that human consciousness may have evolved as an adaptation to anticipate and counter social strategems of other humans, predators, and prey. Alternatively, it has been argued that the recursive circuitry underwriting consciousness is much more primitive, having evolved initially in pre-mammalian species because it improves the capacity for interaction with both social and natural environments by providing an energy saving "neutral" gear in an otherwise energy expensive motor output machine. Once in place, this recursive circuitry may well have provided a basis for the subsequent development of many of the functions which consciousness facilitates in higher organisms, as outlined by Bernard J. Baars.
Cognitive neuroscience approaches
Modern investigations into and discoveries about consciousness are based on psychological statistical studies and case studies of consciousness states and the deficits caused by lesions, stroke, injury, or surgery that disrupt the normal functioning of human senses and cognition. These discoveries suggest that the mind is a complex structure derived from various localized functions that are bound together with a unitary awareness.
Several studies point to common mechanisms in different clinical conditions that lead to loss of consciousness. Persistent vegetative state (PVS) is a condition in which an individual loses the higher cerebral powers of the brain, but maintains sleep-wake cycles with full or partial autonomic functions. Studies comparing PVS with healthy, awake subjects consistently demonstrate an impaired connectivity between the deeper (brainstem and thalamic) and the upper (cortical) areas of the brain. In addition, it is agreed that the general brain activity in the cortex is lower in the PVS state. Some electroneurobiological interpretations of consciousness characterize this loss of consciousness as a loss of the ability to resolve time (similar to playing an old phonographic record at very slow or very rapid speed), along a continuum that starts with inattention, continues on sleep, and arrives to coma and death  . It is likely that different components of consciousness can be teased apart with anesthetics, sedatives and hypnotics. These drugs appear to differentially act on several brain areas to disrupt, to varying degrees, different components of consciousness. The ability to recall information, for example, may be disrupted by anesthetics acting on the hippocampal cortex. Neurons in this region are particularly sensitive to anesthetics at the time loss of recall occurs. Direct anesthetic actions on hippocampal neurons have been shown to underlie EEG effects that occur in humans and animals during loss of recall (MacIver et al 1996; see also: http://www.stanford.edu/group/maciverlab/research.html).
Loss of consciousness also occurs in other conditions, such as general (tonic-clonic) epileptic seizures, in general anaesthesia, maybe even in deep (slow-wave) sleep. At present, the best-supported hypotheses about such cases of loss of consciousness (or loss of time resolution) focus on the need for 1) a widespread cortical network, including particularly the frontal, parietal and temporal cortices, and 2) cooperation between the deep layers of the brain, especially the thalamus, and the upper layers, the cortex. Such hypotheses go under the common term "globalist theories" of consciousness, due to the claim for a widespread, global network necessary for consciousness to interact with non-mental reality in the first place.[How to reference and link to summary or text]
Brain chemistry affects human consciousness. Sleeping drugs (such as Midazolam = Dormicum) can bring the brain from the awake condition (conscious) to the sleep (unconscious). Wake-up drugs such as Anexate reverse this process. Many other drugs (such as alcohol, nicotine, Tetrahydrocannabinol (THC), heroin, cocaine, LSD, MDMA) have a consciousness-changing effect.
There is a neural link between the left and right hemispheres of the brain, known as the corpus callosum. This link is sometimes surgically severed to control severe seizures in epilepsy patients. This procedure was first performed by Roger Sperry in the 1960s. Tests of these patients have shown that, after the link is completely severed, the hemispheres are no longer able to communicate, leading to certain problems that usually arise only in test conditions. For example, while the left side of the brain can verbally describe what is going on in the right visual field, the right hemisphere is essentially mute, instead relying on its spatial abilities to interact with the world on the left visual field. Some say that it is as if two separate minds now share the same skull, but both still represent themselves as a single "I" to the outside world.[How to reference and link to summary or text]
The bilateral removal of the centromedian nucleus (part of the Intra-laminar nucleus of the Thalamus) appears to abolish consciousness, causing coma, PVS, severe mutism and other features that mimic brain death. The centromedian nucleus is also one of the principal sites of action of general anaesthetics and anti-psychotic drugs. This evidence suggests that a functioning thalamus is necessary, but not sufficient, for human consciousness.
Neurophysiological studies in awake, behaving monkeys point to advanced cortical areas in prefrontal cortex and temporal lobes as carriers of neuronal correlates of consciousness. Christof Koch and Francis Crick argued that neuronal mechanisms of consciousness are intricately related to prefrontal cortex — the most advanced cortical area. Rodolfo Llinas proposes that consciousness results from recurrent thalamo-cortical resonance where the specific (dorsal thalamus) thalamocortical system (content) and the non-specific (centromedial thalamus) thalamocortical system (context) interact at gamma band frequency via time coincidence. According to this view the "I" represents a global predictive function required for intentionality. Experimental work of Steven Wise, Mikhail Lebedev and their colleagues supports this view. They demonstrated that activity of prefrontal cortex neurons reflects illusory perceptions of movements of visual stimuli. Nikos Logothetis and colleagues made similar observations on visually responsive neurons in the temporal lobe. These neurons reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry). The studies of blindsight — vision without awareness after lesions to parts of the visual system such as the primary visual cortex — performed by Lawrence Weiskrantz and David P. Carey provided important insights on how conscious perception arises in the brain. In recent years the theory of two visual streams, vision for perception versus vision for action was developed by Melvyn Goodale, David Milner and others. According to this theory, visual perception arises as the result of processing of visual information by the ventral stream areas (located mostly in the temporal lobe), whereas the dorsal stream areas (located mostly in the parietal lobe) process visual information unconsciously. For example, quick catching of the ball would engage mostly the dorsal stream areas, and viewing a painting would be handled by the ventral stream. Overall, these studies show that conscious versus unconscious behaviors can be linked to specific brain areas and patterns of neuronal activation.[How to reference and link to summary or text]. However, neuroscience only focuses on the neural correlates of consciousness. The hard problem of consciousness is to explain how all these flows and electrochemical processes in the brain give rise to the inner experience of subjective awareness.
One of the promising approaches in modern Neuroscience is Operational Architectonicstheory of brain-mind functioning developed by Andrew and Alexander Fingelkurts. This theory states that whenever any pattern of phenomenality (including reflective thought) is instantiated, there is neuro-physiological pattern (revealed directly by EEG) of appropriate kind that corresponds to it. These neuron-physiological EEG patterns (expressed as the virtual operational modules) are brought to existence by joint operations of many functional and transient neuronal assemblies in the brain. The activity of neuronal assemblies per se is 'hidden' in the complex nonstationary structure of EEG field. Therefore, a proper EEG analysis is needed that would be able to reveal the EEG architecture which reflects or instantiates the kind of phenomenal world (considering that there should be the ‘well-defined’ and ‘well-detected’ EEG phenomena) which humans subjectively experience. Currently available EEG methods can reveal the EEG architecture which is amazingly similar to the architecture of a phenomenal world of consciousness (see review on EEG and Operational Architectonics).
Even at the dawn of Newtonian science, Leibniz and many others were suggesting physical theories of consciousness. Modern physical theories of consciousness can be divided into three types: theories to explain behaviour and access consciousness, theories to explain phenomenal consciousness and theories to explain the quantum mechanical (QM) Quantum mind. Theories that seek to explain behaviour are an everyday part of neuroscience, some of these theories of access consciousness, such as Edelman's theory, contentiously identify phenomenal consciousness with reflex events in the brain. Theories that seek to explain phenomenal consciousness directly, such as Space-time theories of consciousness and Electromagnetic theories of consciousness, have been available for almost a century, but have not yet been confirmed by experiment. Theories that attempt to explain the QM measurement problem include Pribram and Bohm's Holonomic brain theory, Hameroff and Penrose's Orch-OR theory and the Many-minds interpretation. 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, and there are philosophers who argue that QM has no bearing on consciousness.
Functions of consciousness
We generally agree that our fellow human beings are conscious, and that much simpler life forms, such as bacteria, are not. Many of us attribute consciousness to higher-order animals such as dolphins and primates; academic research is investigating the extent to which animals are conscious. This suggests the hypothesis that consciousness has co-evolved with life, which would require it to have some sort of added value, especially survival value. People have therefore looked for specific functions and benefits of consciousness. Bernard Baars (1997), for instance, states that "consciousness is a supremely functional adaptation" and suggests a variety of functions in which consciousness plays an important, if not essential, role: prioritization of alternatives, problem solving, decision making, brain processes recruiting, action control, error detection, planning, learning, adaptation, context creation, and access to information.[How to reference and link to summary or text] Antonio Damasio (1999) regards consciousness as part of an organism's survival kit, allowing planned rather than instinctual responses.[How to reference and link to summary or text] He also points out that awareness of self allows a concern for one's own survival, which increases the drive to survive, although how far consciousness is involved in behaviour is an actively debated issue. Many psychologists, such as radical behaviorists, and many philosophers, such as those that support Ryle's approach, would maintain that behavior can be explained by non-conscious processes akin to artificial intelligence, and might consider consciousness to be epiphenomenal or only weakly related to function.
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 (see review in Baars, 2002). This has been called the integration consensus. However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated 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 can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect (cf., Morsella, 2005).
Ervin Laszlo argues that self-awareness, the ability to make observations of oneself, evolved. Emile Durkheim formulated the concept of so called collective consciousness, which is essential for organization of human, social relations. The accelerating drive of human race to explorations, cognition, understanding and technological progress can be explained by some features of collective consciousness (collective self - concepts) and collective intelligence
Tests of consciousness
As there is no clear definition of consciousness and no empirical measure exists to test for its presence, it has been argued that due to the nature of the problem of consciousness, empirical tests are intrinsically impossible. However, several tests have been developed which attempt to provide an operational definition of consciousness and try to determine whether computers and other non-human animals can demonstrate through their behavior, by passing these tests, that they are conscious.
In medicine, several neurological and brain imaging techniques, like EEG and fMRI, have proven useful for physical measures of brain activity associated with consciousness. This is particularly true for EEG measures during anesthesia that can provide an indication of anesthetic depth, although with still limited accuracies of ~ 70 % and a high degree of patient and drug variability seen.
Though often thought of as a test for consciousness, the Turing test (named after computer scientist Alan Turing, who first proposed it) is actually a test to determine whether or not a computer satisfied his operational definition of "intelligent" (which is actually quite different from a test for consciousness or self-awareness). This test is commonly cited in discussion of artificial intelligence. The essence of the test is based on "the Imitation Game", in which a human experimenter attempts to converse, via computer keyboards, with two others. One of the others is a human (who, it is assumed, is conscious) while the other is a computer. Because all of the conversation is via keyboards (teletypes, in Turing's original conception) no cues such as voice, prosody, or appearance will be available to indicate which is the human and which is the computer. If the human is unable to determine which of the conversants is human, and which is a computer, the computer is said to have "passed" the Turing test (satisfied Turing's operational definition of "intelligent").
The Turing test has generated a great deal of research and philosophical debate. For example, Daniel Dennett and Douglas Hofstadter argue that anything capable of passing the Turing test is necessarily conscious, while David Chalmers, argues that a philosophical zombie could pass the test, yet fail to be conscious.
It has been argued that the question itself is excessively anthropomorphic. Edsger Dijkstra commented that "The question of whether a computer can think is no more interesting than the question of whether a submarine can swim", expressing the view that different words are appropriate for the workings of a machine to those of animals even if they produce similar results, just as submarines are not normally said to swim.
Philosopher John Searle developed a thought experiment, the Chinese room argument, which is intended to show problems with the Turing Test. Searle asks the reader to imagine a non-Chinese speaker in a room in which there are stored a very large number of Chinese symbols and rule books. Questions are passed to the person in the form of written Chinese symbols via a slot, and the person responds by looking up the symbols and the correct replies in the rule books. Based on the purely input-output operations, the "Chinese room" gives the appearance of understanding Chinese. However, the person in the room understands no Chinese at all. This argument has been the subject of intense philosophical debate since it was introduced in 1980, even leading to edited volumes on this topic alone.
The application of the Turing test to human consciousness has even led to an annual competition, the Loebner Prize with "Grand Prize of $100,000 and a Gold Medal for the first computer whose responses were indistinguishable from a human's." For a summary of research on the Turing Test, see here.
With the mirror test, devised by Gordon Gallup in the 1970s, one is interested in whether animals are able to recognize themselves in a mirror. The classic example of the test 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. Humans (older than 18 months), great apes (except for gorillas), bottlenose dolphins, pigeons , and elephants  have all been observed to pass this test. The test is usually carried out with an identical 'spot' being placed elsewhere on the head with a non-visible material as a control, to assure the subject is not responding to the touch stimuli of the spot's presence. Proponents of the hard problem of consciousness claim that the mirror test only demonstrates that some animals possess a particular cognitive capacity for modelling their environment, but not for the presence of phenomenal consciousness per se.
One problem researchers face is distinguishing nonconscious reflexes and instinctual responses from conscious responses. Neuroscientists Francis Crick and Christof Koch have proposed that by placing a delay between stimulus and execution of action, one may determine the extent of involvement of consciousness in an action of a biological organism.
For example, when psychologists Larry Squire and Robert Clark combined a tone of a specific pitch with a puff of air to the eye, test subjects came to blink their eyes in anticipation of the puff of air when the appropriate tone was played. When the puff of air followed a half of a second later, no such conditioning occurred. When subjects were asked about the experiment, only those who were asked to pay attention could consciously distinguish which tone preceded the puff of air.
Ability to delay the response to an action implies that the information must be stored in short-term memory, which is conjectured to be a closely associated prerequisite for consciousness. However, this test is only valid for biological organisms. While it is simple to create a computer program that passes, such success does not suggest anything beyond a clever programmer.
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. 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. 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, 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.
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.
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. 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. 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.
Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues. 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. 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. 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.
Although verbal report is in practice the "gold standard" for ascribing consciousness, it is not the only possible criterion. 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. 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. 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.
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. Humans (older than 18 months) and other great apes, bottlenose dolphins, pigeons, and elephants have all been observed to pass this test.
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.
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. 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.
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. 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. 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).
In 2011 Graziano and Kastner 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":
- "We have no idea how consciousness emerges from the physical activity of the brain and we do not know whether consciousness can emerge from non-biological systems, such as computers ... At this point the reader will expect to find a careful and precise definition of consciousness. You will be disappointed. Consciousness has not yet become a scientific term that can be defined in this way. Currently we all use the term consciousness in many different and often ambiguous ways. Precise definitions of different aspects of consciousness will emerge ... but to make precise definitions at this stage is premature."
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  states "consciousness is the sum of the electrical discharges occurring throughout the nervous system of a being at any given instant". 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.
To properly understand the definition of consciousness, three principal meanings have been developed and it is critical to distinguish them. Firstly, consciousness can be defined as the waking state. This essentially means that to be conscious, one needs to be awake, aroused, alert or vigilant. The stages of consciousness can range from wakefulness, to sleep to coma even. Secondly, consciousness is defined as experience, a far more subjective approach. This notion suggests that consciousness is the content of experience from one moment to another. Consciousness is highly personal, involving a conscious subject with a limited point of view. Thirdly, consciousness can be defined as the mind. Any mental state with a propositional content is considered conscious. Thus this includes beliefs, fears, hopes, intentions, expectations and desires 
Christof Koch lists the following four definitions of consciousness in his latest book, 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.
Biological function and evolution
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. 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. 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. Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see 
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. 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. In his paper "Evolution of consciousness," John Eccles argued that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness. 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. 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. 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. 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. 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.
States of consciousness
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. 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.
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.
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. 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.
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.
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. 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.
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. 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.
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. 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. 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. Most psychologists and neuroscientists reject 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.
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. 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.
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. 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. 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".
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.
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. Also, bioethicists may be concerned with the ethical implications of consciousness in medical cases of patients such as Karen Ann Quinlan, while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works.
In medicine, consciousness is examined using a set of procedures known as neuropsychological assessment. 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.
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.
Disorders of consciousness
Medical conditions that inhibit consciousness are considered disorders of consciousness. 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. Differential diagnosis of these disorders is an active area of biomedical research. Finally, brain death results in an irreversible disruption of consciousness. 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.
|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.|
- 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. 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.
Stream of consciousness
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". 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.
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.
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.
- Further information: Level of consciousness (esotericism)
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. 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. 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.
- Consciousness (Buddhism)
- Higher Consciousness
- 8-Circuit Model of Consciousness
- Donald Davidson's swamp man thought experiment ("Knowing One Own's Mind", 1987)
- Dream argument
- False Consciousness (Marxism)
- Freedom of thought
- Mental body
- Mind at Large
- Mind-body problem
- Multiple Drafts theory (Daniel Dennett) cf. also Marvin Minsky
- New Mysterianism
- Personhood Theory
- Philosophy of mind
- Philosophy of perception
- Political consciousness, pertaining to marxist and post-marxist conceptions of consciousness.
- Stream of consciousness
- Theory of mind
Physical Hypotheses about Consciousness
- Orch-OR theory
- Electromagnetic theories of consciousness
- Holonomic brain theory
- Quantum mind
- Space-time theories of consciousness
- Simulated Reality
- Association for Consciousness Exploration
- Association for the Scientific Study of Consciousness
- Mind and Life Institute
- Mind Science Foundation
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- Morsella, E. (2005). The Function of Phenomenal States: Supramodular Interaction Theory. Psychological Review, 112, 1000-1021.
- Penrose, R., Hameroff, S. R. (1996), 'Conscious Events as Orchestrated Space-Time Selections', Journal of Consciousness Studies, 3 (1), pp. 36-53.
- Shanon, B. (1998). What is the function of consciousness? Journal of Consciousness Studies, 5, 295-308.
- Anthropology of Consciousness
- Journal of Consciousness Studies
- Consciousness and Cognition
- Science & Consciousness Review
- ASSC e-print archive containing articles, book chapters, theses, conference presentations by members of the ASSC.
- Publications of the Tufts Center for Cognitive Studies, including Daniel Dennett
- David Chalmers' directory of online papers on consciousness
- Intuitions about Consciousness: Experimental Studies an article describing the folk intuitions about what is a conscious agent
- Stanford Encyclopedia of Philosophy:
- Internet Encyclopedia of Philosophy:
- History of Consciousness Graduate Program, ("consciousness as forms of human expression and social action manifested in historical, cultural, and political contexts") at the University of California, Santa Cruz, headed by Dr. Angela Davis* Online lecture videos, from an undergraduate course taught by Christof Koch at Caltech on the neurobiological basis of consciousness in 2004.
- Piero Scaruffi's annotated bibliography on the mind
- Anesthesia and Drug effects on consciousness
- Brain Atlas, Brain Maps, Neuroinformatics
- Online course in consciousness at University of Virginia
- A survey course at University of Florida
- Edinburgh thesis (.ps) on consciousness including up-to-date reviews
- Consciousness-Related Engineering Anomaly Princeton
- Thy Mystery of Consciousness TIME.com
- Helen Keller Language and Consciousness
- Theory of the Red Blood Cells
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