Consciousness
Consciousness is the quality or state of self-awareness,
or, 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 computing machines
like computers or robots to be conscious as
studied in the field of artificial intelligence.
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, neuropsychology and
neuroscience. The primary focus is on understanding
what it means biologically and psychologically
for information to be present in consciousness—that
is, on determining the neural and psychological
correlates of consciousness. The majority
of experimental studies assess consciousness
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 drugs and alcohol, 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.
Etymology and early history
The origin of the modern concept of consciousness
is often attributed to John Locke's Essay
Concerning Human Understanding, published
in 1690. Locke defined consciousness as "the
perception of what passes in a man's own mind".
His essay influenced the 18th-century view
of consciousness, and his definition appeared
in Samuel Johnson's celebrated Dictionary
(1755).
The earliest English language uses of "conscious"
and "consciousness" date back, however, to
the 1500s. The English word "conscious" originally
derived from the Latin conscius (con- "together"
and scio "to know"), but the Latin word did
not have the same meaning as our word—it
meant "knowing with", in other words "having
joint or common knowledge with another". There
were, however, many occurrences in Latin writings
of the phrase conscius sibi, which translates
literally as "knowing with oneself", or in
other words "sharing knowledge with oneself
about something". This phrase had the figurative
meaning of "knowing that one knows", as the
modern English word "conscious" does. In its
earliest uses in the 1500s, the English word
"conscious" retained the meaning of the Latin
conscius. For example, Thomas Hobbes in Leviathan
wrote: "Where two, or more men, know of one
and the same fact, they are said to be Conscious
of it one to another." The Latin phrase conscius
sibi, whose meaning was more closely related
to the current concept of consciousness, was
rendered in English as "conscious to oneself"
or "conscious unto oneself". For example,
Archbishop Ussher wrote in 1613 of "being
so conscious unto myself of my great weakness".
Locke's definition from 1690 illustrates that
a gradual shift in meaning had taken place.
A related word was conscientia, which primarily
means moral conscience. In the literal sense,
"conscientia" means knowledge-with, that is,
shared knowledge. The word first appears in
Latin juridical texts by writers such as Cicero.
Here, conscientia is the knowledge that a
witness has of the deed of someone else. René
Descartes (1596–1650) is generally taken
to be the first philosopher to use "conscientia"
in a way that does not fit this traditional
meaning. Descartes used "conscientia" the
way modern speakers would use "conscience".
In Search after Truth he says "conscience
or internal testimony" (conscientia vel interno
testimonio).
In the dictionary
The dictionary meaning of the word consciousness
extends through several centuries and associated
cognate meanings which have ranged from formal
definitions to somewhat more skeptical definitions.
One formal definition indicating the range
of these cognate meanings is given in Webster's
Third New International Dictionary stating
that consciousness is: "(1) a. awareness or
perception of an inward psychological or spiritual
fact: intuitively perceived knowledge of something
in one's inner self. b. inward awareness of
an external object, state, or fact. c: concerned
awareness: INTEREST, CONCERN -- often used
with an attributive noun. (2): the state or
activity that is characterized by sensation,
emotion, volition, or thought: mind in the
broadest possible sense: something in nature
that is distinguished from the physical. (3):
the totality in psychology of sensations,
perceptions, ideas, attitudes and feelings
of which an individual or a group is aware
at any given time or within a particular time
span -- compare STREAM OF CONSCIOUSNESS."
Philosophy of mind
The philosophy of mind has given rise to many
stances regarding consciousness. The Routledge
Encyclopedia of Philosophy in 1998 defines
consciousness as follows:
In a more skeptical definition of consciousness,
Stuart Sutherland has exemplified some of
the difficulties in fully ascertaining all
of its cognate meanings in his entry for the
1989 version of the Macmillan Dictionary of
Psychology:
Most writers on the philosophy of consciousness
have been concerned to defend a particular
point of view, and have organized their material
accordingly. For surveys, the most common
approach is to follow a historical path by
associating stances with the philosophers
who are most strongly associated with them,
for example Descartes, Locke, Kant, etc. An
alternative is to organize philosophical stances
according to basic issues.
The validity of the concept
Philosophers and non-philosophers differ in
their intuitions about what consciousness
is. While most people have a strong intuition
for the existence of what they refer to as
consciousness, skeptics argue that this intuition
is false, either because the concept of consciousness
is intrinsically incoherent, or because our
intuitions about it are based in illusions.
Gilbert Ryle, for example, argued that traditional
understanding of consciousness depends on
a Cartesian dualist outlook that improperly
distinguishes between mind and body, or between
mind and world. He proposed that we speak
not of minds, bodies, and the world, but of
individuals, or persons, acting in the world.
Thus, by speaking of "consciousness" we end
up misleading ourselves by thinking that there
is any sort of thing as consciousness separated
from behavioral and linguistic understandings.
More generally, many philosophers and scientists
have been unhappy about the difficulty of
producing a definition that does not involve
circularity or fuzziness.
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.
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 may provide 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 publications
by G. Guerreshi, J. Cia, S. Popescu, and H.
Briegel 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. Related issues have also
been studied extensively by Greg Littmann
of the University of Illinois. and Colin Allen
a professor at Indiana University regarding
the literature and research studying artificial
intelligence in androids.
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.
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.
Artifact 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:
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. A third
group of scholars have argued that with technological
growth once machines begin to display any
substantial signs of human-like behavior then
the dichotomy (of human consciousness compared
to human-like consciousness) becomes passe
and issues of machine autonomy begin to prevail
even as observed in its nascent form within
contemporary industry and technology.
In a lively exchange over what has come to
be referred to as "the Chinese room argument",
John Searle sought to refute the claim of
proponents of what he calls "strong artificial
intelligence (AI)" that a computer program
can be conscious, though he does agree with
advocates of "weak AI" that computer programs
can be formatted to "simulate" conscious states.
His own view is that consciousness has subjective,
first-person causal powers by being essentially
intentional due simply to the way human brains
function biologically; conscious persons can
perform computations, but consciousness is
not inherently computational the way computer
programs are. To make a Turing machine that
speaks Chinese, Searle imagines a room stocked
with computers and algorithms programmed to
respond to Chinese questions, i.e., Turing
machines, programmed to correctly answer in
Chinese any questions asked in Chinese. Searle
argues that with such a machine, he would
be able to process the inputs to outputs perfectly
without having any understanding of Chinese,
nor having any idea what the questions and
answers could possibly mean. 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 would pass the Turing
test of answering the questions in both languages,
but he is only conscious of what he is doing
when he speaks English. Another way of putting
the argument is to say that 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,
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.
Scientific study
For many decades, consciousness as a research
topic was avoided by the majority of mainstream
scientists, because of a general feeling that
a phenomenon defined in subjective terms could
not properly be studied using objective experimental
methods. 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 medical and psychological investigations
into consciousness are based on psychological
experiments (including, for example, the investigation
of priming effects using subliminal stimuli),
and on case studies of alterations in consciousness
produced by trauma, illness, or drugs. Broadly
viewed, scientific approaches are based on
two core concepts. The first identifies the
content of consciousness with the experiences
that are reported by human subjects; the second
makes use of the concept of consciousness
that has been developed by neurologists and
other medical professionals who deal with
patients whose behavior is impaired. In either
case, the ultimate goals are to develop techniques
for assessing consciousness objectively in
humans as well as other animals, and to understand
the neural and psychological mechanisms that
underlie it.
Measurement
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.
Neural correlates
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.
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
a virtually unlimited number of different
possible scenes and details (differentiation)
because it integrates those details from our
sensory systems, while the integrative nature
of consciousness in this view easily explains
how our experience can seem unified as one
whole despite all of these individual parts.
However, it remains unspecified which kinds
of information are integrated in a conscious
manner and which kinds can be integrated without
consciousness. Nor is it explained what specific
causal role conscious integration plays, nor
why the same functionality cannot be achieved
without consciousness. Obviously not all kinds
of information are capable of being disseminated
consciously (e.g., neural activity related
to vegetative functions, reflexes, unconscious
motor programs, low-level perceptual analyses,
etc.) and many kinds of information can be
disseminated and combined with other kinds
without consciousness, as in intersensory
interactions such as the ventriloquism effect.
Hence it remains unclear why any of it is
conscious. For a review of the differences
between conscious and unconscious integrations,
see the article of E. Morsella.
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 article "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. Others, still, argue about
all these theories.
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 and alcohol
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 as well understood as
alcoholism, 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
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,
and (2) memory. Signals arising from sensory
organs are transmitted to the brain and then
processed in a series of stages, which extract
multiple types of information from the raw
input. In the visual system, for example,
sensory signals from the eyes are transmitted
to the thalamus and then to the primary visual
cortex; inside the cerebral cortex they are
sent to areas that extract features such as
three-dimensional structure, shape, color,
and motion. 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".
Medical aspects
The medical approach to consciousness is practically
oriented. It derives from a need to treat
people whose brain function has been impaired
as a result of disease, brain damage, toxins,
or drugs. In medicine, conceptual distinctions
are considered useful to the degree that they
can help to guide treatments. Whereas the
philosophical approach to consciousness focuses
on its fundamental nature and its contents,
the medical approach focuses on the amount
of consciousness a person has: in medicine,
consciousness is assessed as a "level" ranging
from coma and brain death at the low end,
to full alertness and purposeful responsiveness
at the high end.
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.
Assessment
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 "alert and oriented
times four" (sometimes denoted "A&Ox4" 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.
In 2013, an experimental procedure was developed
to measure degrees of consciousness, the procedure
involving stimulating the brain with a magnetic
pulse, measuring resulting waves of electrical
activity, and developing a consciousness score
based on the complexity of the brain activity.
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.
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:
Spiritual approaches
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.
