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发表于 2011-1-23 13:44
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! ]* S; D" P9 r% X/ dConsciousness is variously defined as subjective experience, awareness, the ability to experience "feeling", wakefulness, the understanding of the concept "self", or the executive control system of the mind.[1] It is an umbrella term that may refer to a variety of mental phenomena.[2] Although humans realize what everyday experiences are, consciousness itself resists being defined, philosophers note (e.g. John Searle in The Oxford Companion to Philosophy):[3]"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."1 }' `" h0 k Q4 p! Q( Y6 L' T/ @
—Schneider and Velmans, 2007[4]
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Consciousness in medicine (e.g., anesthesiology) is assessed by observing a patient's alertness and responsiveness, and can be seen as a continuum of states ranging from alert, oriented to time and place, and communicative, through disorientation, then delirium, then loss of any meaningful communication, and ending with loss of movement in response to painful stimulation.[5]
# t a( V6 a! m! ]8 fConsciousness in psychology and philosophy typically means something beyond what it means for anesthesiology, and may be said in many contexts to imply four characteristics: subjectivity, change, continuity, and selectivity.[1][6] Philosopher Franz Brentano has suggested intentionality or aboutness (that consciousness is about something). However, within the philosophy of mind there is no consensus on whether intentionality is a requirement for consciousness.[7]9 X* Z9 W& m, k, U3 ~9 P4 t) S
Consciousness is the subject of much research in philosophy of mind, psychology, neuroscience, cognitive science and artificial intelligence. Issues of practical concern include how the presence of consciousness can be assessed in severely ill or comatose people;[8] whether non-human consciousness exists and if so how it can be measured; at what point in fetal development consciousness begins; and whether computers can achieve a conscious state.[9][10][11]
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Etymology& _0 `0 q2 P4 U+ P
The word "conscious" is derived from Latin conscius meaning "1. having joint or common knowledge with another, privy to, cognizant of; 2. conscious to oneself; esp., conscious of guilt".[12] A related word was conscientia, which primarily means moral conscience. In the literal sense, "conscientia" means knowledge-with, that is, shared knowledge. The word first appears in Latin juridical texts by writers such as Cicero.[13] Here, conscientia is the knowledge that a witness has of the deed of someone else.[14]$ _3 X% g9 I( h) N9 ^: ~) b$ T
René Descartes (1596–1650) is generally taken to be the first philosopher to use "conscientia" in a way that does not seem to fit this traditional meaning.[citation needed] Descartes used "conscientia" the way modern speakers would use "conscience." In Search after Truth he says "conscience or internal testimony" (conscientia vel interno testimonio).[15]- v- J, ^) h2 g; O4 X
Shortly thereafter, in Britain, the neo-Platonist theologian Ralph Cudworth used the modern meaning of consciousness in his "True Intellectual System of the Universe" (1678) and associated the concept with personal identity, which is assured by the repeated consciousness of oneself. Cudworth's use of the term also remained intertwined with moral agency.[citation needed] While there were no elaborate theories of consciousness in the seventeenth century, there was an awareness of the idea of consciousness. Cudworth was the first English philosopher to make extensive use of the noun "consciousness" with a specific philosophical meaning.[16]8 w p0 o- a$ V/ b
Twelve years later, Locke in Essay Concerning Human Understanding (1690) connected consciousness with personal identity.[17] Locke argued that being the same person from one time to another was not dependent upon having the same soul or same body, but instead the same consciousness.[18] Locke defined consciousness as “the perception of what passes in a man’s own mind.”[19] Locke had much influence on the 18th Century view of consciousness: in Samuel Johnson's celebrated Dictionary (1755), Johnson uses this definition of "consciousness."[citation needed]# C2 J: v! a) l+ {6 g( M
Events that occur in the mind or brain that are not within phenomenal or access consciousness are known as subconscious events.' _2 ~2 F! h/ q3 Z' j# U8 y6 j: W
Philosophical approaches
, W O6 F: a8 y j+ vThere are many philosophical stances on consciousness, including behaviorism, dualism, idealism, functionalism, reflexive monism, phenomenalism, phenomenology and intentionality, physicalism, emergentism, mysticism, personal identity, and externalism.
- O9 m, j# K% iPhenomenal and access consciousness
- S6 `" ~7 U% M8 O4 S$ {$ u' w2 g& RPhenomenal consciousness (P-consciousness) is simply experience;[20] 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. The hard problem of consciousness, formulated by David Chalmers in 1996, deals with the issue of "how to explain a state of phenomenal consciousness in terms of its neurological basis".[21] H6 R/ S* F& q( M4 M4 }% m
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. Daniel 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. Dennett suggests that what people think of as phenomenal consciousness, such as qualia, are judgments and consequent behavior.[22] He extends this analysis 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."[22] Chalmers, on the other hand, argues that Dennett's explanatory processes merely address aspects of the easy problem. Eccles and others have pointed out the difficulty of explaining the evolution of qualia, or of 'minds', which experience them, given that all the processes governing evolution are physical and so have no direct access to them. There is no guarantee that all people have minds, nor any way to verify whether one does or does not possess one.: f1 t+ Z$ U+ {5 m
The description and location of phenomenal consciousness
4 m5 \0 n D: a4 \/ CFor centuries, philosophers have investigated phenomenal consciousness. René Descartes, who coined the famous dictum 'cogito ergo sum', wrote Meditations on First Philosophy in the seventeenth century.[23] According to Descartes, all thought is conscious.[24] Conscious experience, according to Descartes, included such ideas as imaginings and perceptions laid out in space and time that are viewed from a point, and appearing as a result of some quality such as color, smell, and so on. (Modern readers are often confused by this Descartes' notion of interchangeability between the terms 'idea' and 'imaginings.')[citation needed]2 C0 T+ }; E* n* F
Descartes defines ideas as extended things, as in this excerpt from his Treatise on Man:! ]4 A/ U; _% R0 I& g9 Y
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 that 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.[25] & E. V9 ]6 p# h) r1 q _/ {, G
Thus Descartes does not identify mental ideas with activity within the sense organs, or even with brain activity, but rather with the "forms or images" that unite the 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, appears to be singular. Thus he extrapolated from this that it was the mediator between body and soul.[25]; o" b+ l4 ~. l. ^9 @3 m+ R! C! ?! t
Philosophical responses, including those of Nicolas Malebranche, Thomas Reid, John Locke, David Hume and Immanuel Kant, were varied. 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. 7 _8 `7 s. E: K
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'.[26] David Hume and Immanuel Kant also differ from Descartes, in that they avoid mentioning a place from which experience is viewed; certainly, few if any modern philosophers have identified the pineal gland as the seat of dualist interaction.0 Y: Q; I# O- U* y1 n
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.[27] 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.* T, V# [) R' N' Y$ h
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." C+ K3 b; U3 s, D9 f$ \1 Y6 C
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.
& t. h% g; k' W5 ~+ g5 r2 MSome 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,[28] reflexive monism, and Electromagnetic theories of consciousness to explain the correspondence between brain activity and experience.2 r, j Y" D O
Parapsychologists and some philosophers e.g. Stephen Braude sometimes appeal to the concepts of psychokinesis or telepathy to support the belief that consciousness is not confined to the brain. |
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