The term "sentience" can be used when specifically designating ethical considerations stemming from a form of phenomenal consciousness (P-consciousness, or the ability to feel qualia). Since sentience involves the ability to experience ethically positive or negative (i.e., valenced) mental states, it may justify welfare concerns and legal protection, as with non-human animals.
Some scholars believe that consciousness is generated by the interoperation of various parts of the brain; these mechanisms are labeled the neural correlates of consciousness (NCC). Some further believe that constructing a system (e.g., a computer system) that can emulate this NCC interoperation would result in a system that is conscious. Some scholars reject the possibility of artificial consciousness.
Philosophical views
As there are many hypothesized types of consciousness,
there are many potential implementations of artificial consciousness.
In the philosophical literature, perhaps the most common taxonomy of
consciousness is into "access" and "phenomenal" variants. Access
consciousness concerns those aspects of experience
that can be apprehended, while phenomenal consciousness concerns those
aspects of experience that seemingly cannot be apprehended, instead
being characterized qualitatively in terms of "raw feels", "what it is
like" or qualia.
Plausibility debate
Type-identity theorists
and other skeptics hold the view that consciousness can be realized
only in particular physical systems because consciousness has properties
that necessarily depend on physical constitution. In his 2001 article "Artificial Consciousness: Utopia or Real Possibility," Giorgio Buttazzo
says that a common objection to artificial consciousness is that,
"Working in a fully automated mode, they [the computers] cannot exhibit
creativity, unreprogrammation (which means can 'no longer be
reprogrammed', from rethinking), emotions, or free will. A computer, like a washing machine, is a slave operated by its components."
For other theorists (e.g., functionalists),
who define mental states in terms of causal roles, any system that can
instantiate the same pattern of causal roles, regardless of physical
constitution, will instantiate the same mental states, including
consciousness.
Thought experiments
The
"fading qualia" (left) and the "dancing qualia" (right) are two thought
experiments about consciousness and brain replacement. Chalmers argues
that both are contradicted by the lack of reaction of the subject to
changing perception, and are thus impossible in practice. He concludes
that the equivalent silicon brain will have the same perceptions as the
biological brain.
David Chalmers proposed two thought experiments intending to demonstrate that "functionally isomorphic"
systems (those with the same "fine-grained functional organization",
i.e., the same information processing) will have qualitatively identical
conscious experiences, regardless of whether they are based on
biological neurons or digital hardware.
The "fading qualia" is a reductio ad absurdum
thought experiment. It involves replacing, one by one, the neurons of a
brain with a functionally identical component, for example based on a silicon chip. Chalmers makes the hypothesis,
knowing it in advance to be absurd, that "the qualia fade or disappear"
when neurons are replaced one-by-one with identical silicon
equivalents. Since the original neurons and their silicon counterparts
are functionally identical, the brain's information processing should
remain unchanged, and the subject's behaviour and introspective reports
would stay exactly the same. Chalmers argues that this leads to an
absurd conclusion: the subject would continue to report normal conscious
experiences even as their actual qualia fade away. He concludes that
the subject's qualia actually don't fade, and that the resulting robotic
brain, once every neuron is replaced, would remain just as sentient as
the original biological brain.
Similarly, the "dancing qualia" thought experiment is another reductio ad absurdum
argument. It supposes that two functionally isomorphic systems could
have different perceptions (for instance, seeing the same object in
different colors, like red and blue). It involves a switch that
alternates between a chunk of brain that causes the perception of red,
and a functionally isomorphic silicon chip, that causes the perception
of blue. Since both perform the same function within the brain, the
subject would not notice any change during the switch. Chalmers argues
that this would be highly implausible if the qualia were truly switching
between red and blue, hence the contradiction. Therefore, he concludes
that the equivalent digital system would not only experience qualia, but
it would perceive the same qualia as the biological system (e.g.,
seeing the same color).
Critics object that Chalmers' proposal begs the question in
assuming that all mental properties and external connections are already
sufficiently captured by abstract causal organization. Van Heuveln et
al. argue that the dancing qualia argument contains an equivocation
fallacy, conflating a "change in experience" between two systems with an
"experience of change" within a single system. Mogensen argues that the fading qualia argument can be resisted by
appealing to vagueness at the boundaries of consciousness and the
holistic structure of conscious neural activity, which suggests
consciousness may require specific biological substrates rather than
being substrate-independent.
Greg Egan's short story Learning To Be Me (mentioned in §In fiction), illustrates how undetectable duplication of the brain and its functionality could be from a first-person perspective.
In large language models
In 2022, Google engineer Blake Lemoine made a viral claim that Google's LaMDA
chatbot was sentient. Lemoine supplied as evidence the chatbot's
humanlike answers to many of his questions; however, the chatbot's
behavior was judged by the scientific community as likely a consequence
of mimicry, rather than machine sentience. Lemoine's claim was widely
derided for being ridiculous. Moreover, attributing consciousness based solely on the basis of LLM
outputs or the immersive experience created by an algorithm is
considered a fallacy. However, while philosopher Nick Bostrom
states that LaMDA is unlikely to be conscious, he additionally poses
the question of "what grounds would a person have for being sure about
it?" One would have to have access to unpublished information about
LaMDA's architecture, and also would have to understand how
consciousness works, and then figure out how to map the philosophy onto
the machine: "(In the absence of these steps), it seems like one should
be maybe a little bit uncertain.[...] there could well be other systems now, or in the relatively near future, that would start to satisfy the criteria."
David Chalmers
argued in 2023 that LLMs today display impressive conversational and
general intelligence abilities, but are likely not conscious yet, as
they lack some features that may be necessary, such as recurrent
processing, a global workspace,
and unified agency. Nonetheless, he considers that non-biological
systems can be conscious, and suggested that future, extended models
(LLM+s) incorporating these elements might eventually meet the criteria
for consciousness, raising both profound scientific questions and
significant ethical challenges. However, the view that consciousness can exist without biological phenomena is controversial and some reject it.
Kristina Šekrst cautions that anthropomorphic terms such as "hallucination" can obscure important ontological differences between artificial and human cognition. While LLMs may produce human-like outputs, she argues that it does not
justify ascribing mental states or consciousness to them. Instead, she
advocates for an epistemological framework (such as reliabilism) that recognizes the distinct nature of AI knowledge production. She suggests that apparent understanding in LLMs may be a sophisticated
form of AI hallucination. She also questions what would happen if an
LLM were trained without any mention of consciousness.
Testing
Sentience is an inherently first-person phenomenon. Because of that,
and due the lack of an empirical definition of sentience, directly
measuring it may be impossible. Although systems may display numerous
behaviors correlated with sentience, determining whether a system is
sentient is known as the hard problem of consciousness.
In the case of AI, there is the additional difficulty that the AI may
be trained to act like a human, or incentivized to appear sentient,
which makes behavioral markers of sentience less reliable. Additionally, some chatbots have been trained to say they are not conscious.
A well-known method for testing machine intelligence is the Turing test,
which assesses the ability to have a human-like conversation. But
passing the Turing test does not indicate that an AI system is sentient,
as the AI may simply mimic human behavior without having the associated
feelings.
In 2014, Victor Argonov suggested a non-Turing test for machine
sentience based on machine's ability to produce philosophical judgments. He argues that a deterministic machine must be regarded as conscious if
it is able to produce judgments on all problematic properties of
consciousness (such as qualia or binding)
having no innate (preloaded) philosophical knowledge on these issues,
no philosophical discussions while learning, and no informational models
of other creatures in its memory (such models may implicitly or
explicitly contain knowledge about these creatures' consciousness).
However, this test can be used only to detect, but not refute the
existence of consciousness. Just as with the Turing Test: a positive
result proves that machine is conscious but a negative result proves
nothing. For example, absence of philosophical judgments may be caused
by lack of the machine's intellect, not by absence of consciousness.
If it were suspected that a particular machine was conscious, its rights would be an ethical issue that would need to be assessed (e.g. what rights it would have under law). For example, a conscious computer that was owned and used as a tool or
central computer within a larger machine is a particular ambiguity.
Should laws
be made for such a case? Consciousness would also require a legal
definition in this particular case. Because artificial consciousness is
still largely a theoretical subject, such ethics have not been discussed
or developed to a great extent, though it has often been a theme in
fiction.
AI sentience would give rise to concerns of welfare and legal protection, whereas other aspects of consciousness related to cognitive capabilities may be more relevant for AI rights.
Sentience is generally considered sufficient for moral
consideration, but some philosophers consider that moral consideration
could also stem from other notions of consciousness, or from
capabilities unrelated to consciousness, such as: "having a sophisticated conception of oneself as persisting
through time; having agency and the ability to pursue long-term plans;
being able to communicate and respond to normative reasons; having
preferences and powers; standing in certain social relationships with
other beings that have moral status; being able to make commitments and
to enter into reciprocal arrangements; or having the potential to
develop some of these attributes."
Ethical concerns still apply (although to a lesser extent) when the consciousness is uncertain, as long as the probability is deemed non-negligible. The precautionary principle is also relevant if the moral cost of mistakenly attributing or denying moral consideration to AI differs significantly.
In 2021, German philosopher Thomas Metzinger
argued for a global moratorium on synthetic phenomenology until 2050.
Metzinger asserts that humans have a duty of care towards any sentient
AIs they create, and that proceeding too fast risks creating an
"explosion of artificial suffering". David Chalmers also argued that creating conscious AI would "raise a
new group of difficult ethical challenges, with the potential for new
forms of injustice".
Bernard Baars and others argue there are various aspects of consciousness necessary for a machine to be artificially conscious. The functions of consciousness suggested by Baars are: definition and
context setting, adaptation and learning, editing, flagging and
debugging, recruiting and control, prioritizing and access-control,
decision-making or executive function, analogy-forming function,
metacognitive and self-monitoring function, and autoprogramming and
self-maintenance function. Igor Aleksander suggested 12 principles for artificial consciousness: the brain is a state machine, inner neuron partitioning, conscious and
unconscious states, perceptual learning and memory, prediction, the
awareness of self, representation of meaning, learning utterances,
learning language, will, instinct, and emotion. The aim of AC is to
define whether and how these and other aspects of consciousness can be
synthesized in an engineered artifact such as a digital computer. This
list is not exhaustive; there are many others not covered.
Subjective experience
Some philosophers, such as David Chalmers, use the term consciousness to refer exclusively to phenomenal consciousness, which is roughly equivalent to sentience. Others use the word sentience to refer exclusively to valenced (ethically positive or negative) subjective experiences, like pleasure or suffering. Explaining why and how subjective experience arises is known as the hard problem of consciousness.
Awareness
Awareness could be one required aspect, but there are many problems with the exact definition of awareness. The results of the experiments of neuroscanning on monkeys
suggest that a process, not only a state or object, activates neurons.
Awareness includes creating and testing alternative models of each
process based on the information received through the senses or
imagined,and is also useful for making predictions. Such modeling needs a lot of
flexibility. Creating such a model includes modeling the physical
world, modeling one's own internal states and processes, and modeling
other conscious entities.
There are at least three types of awareness: agency awareness, goal awareness, and sensorimotor awareness, which may
also be conscious or not. For example, in agency awareness, you may be
aware that you performed a certain action yesterday, but are not now
conscious of it. In goal awareness, you may be aware that you must
search for a lost object, but are not now conscious of it. In
sensorimotor awareness, you may be aware that your hand is resting on an
object, but are not now conscious of it.
Because objects of awareness are often conscious, the distinction
between awareness and consciousness is frequently blurred or they are
used as synonyms.
Memory
Conscious events interact with memory systems in learning, rehearsal, and retrieval. The IDA model elucidates the role of consciousness in the updating of perceptual memory, transient episodic memory, and procedural memory.
Transient episodic and declarative memories have distributed
representations in IDA; there is evidence that this is also the case in
the nervous system. In IDA, these two memories are implemented computationally using a modified version of Kanerva's sparse distributed memory architecture.
Learning
Learning is also considered necessary for artificial consciousness.
Per Bernard Baars, conscious experience is needed to represent and adapt
to novel and significant events. Per Axel Cleeremans and Luis Jiménez, learning is defined as "a set of philogenetically [sic]
advanced adaptation processes that critically depend on an evolved
sensitivity to subjective experience so as to enable agents to afford
flexible control over their actions in complex, unpredictable
environments".
Anticipation
The ability to predict (or anticipate) foreseeable events is considered important for artificial intelligence by Igor Aleksander.[52] The emergentist multiple drafts principle proposed by Daniel Dennett in Consciousness Explained
may be useful for prediction: it involves the evaluation and selection
of the most appropriate "draft" to fit the current environment.
Anticipation includes prediction of consequences of one's own proposed
actions and prediction of consequences of probable actions by other
entities.
Relationships between real world states are mirrored in the state
structure of a conscious organism, enabling the organism to predict
events. An artificially conscious machine should be able to anticipate events
correctly in order to be ready to respond to them when they occur or to
take preemptive action to avert anticipated events. The implication here
is that the machine needs flexible, real-time components that build
spatial, dynamic, statistical, functional, and cause-effect models of
the real world and predicted worlds, making it possible to demonstrate
that it possesses artificial consciousness in the present and future and
not only in the past. In order to do this, a conscious machine should
make coherent predictions and contingency plans, not only in worlds with
fixed rules like a chess board, but also for novel environments that
may change, to be executed only when appropriate to simulate and control
the real world.
Functionalism
is a theory that defines mental states by their functional roles (their
causal relationships to sensory inputs, other mental states, and
behavioral outputs), rather than by their physical composition.
According to this view, what makes something a particular mental state,
such as pain or belief, is not the material it is made of, but the role
it plays within the overall cognitive system. It allows for the
possibility that mental states, including consciousness, could be
realized on non-biological substrates, as long as it instantiates the
right functional relationships. Functionalism is particularly popular among philosophers.
A 2023 study suggested that current large language models
probably don't satisfy the criteria for consciousness suggested by
these theories, but that relatively simple AI systems that satisfy these
theories could be created. The study also acknowledged that even the
most prominent theories of consciousness remain incomplete and subject
to ongoing debate.
Stan Franklin created a cognitive architecture called LIDA that implements Bernard Baars's theory of consciousness called the global workspace theory. It relies heavily on codelets,
which are "special purpose, relatively independent, mini-agent[s]
typically implemented as a small piece of code running as a separate
thread." Each element of cognition, called a "cognitive cycle" is
subdivided into three phases: understanding, consciousness, and action
selection (which includes learning). LIDA reflects the global workspace
theory's core idea that consciousness acts as a workspace for
integrating and broadcasting the most important information, in order to
coordinate various cognitive processes.
The CLARION cognitive architecture models the mind using a two-level
system to distinguish between conscious ("explicit") and unconscious
("implicit") processes. It can simulate various learning tasks, from
simple to complex, which helps researchers study in psychological
experiments how consciousness might work.
OpenCog
Ben Goertzel made an embodied AI through the open-source OpenCog
project. The code includes embodied virtual pets capable of learning
simple English-language commands, as well as integration with real-world
robotics, done at the Hong Kong Polytechnic University.
Connectionist
Haikonen's cognitive architecture
Pentti Haikonen considers classical rule-based computing inadequate
for achieving AC: "the brain is definitely not a computer. Thinking is
not an execution of programmed strings of commands. The brain is not a
numerical calculator either. We do not think by numbers." Rather than
trying to achieve mind and consciousness by identifying and implementing their underlying computational rules, Haikonen proposes "a special cognitive architecture to reproduce the processes of perception, inner imagery, inner speech, pain, pleasure, emotions and the cognitive
functions behind these. This bottom-up architecture would produce
higher-level functions by the power of the elementary processing units,
the artificial neurons, without algorithms or programs".
Haikonen believes that, when implemented with sufficient complexity,
this architecture will develop consciousness, which he considers to be
"a style and way of operation, characterized by distributed signal
representation, perception process, cross-modality reporting and
availability for retrospection."
Haikonen is not alone in this process view of consciousness, or the view that AC will spontaneously emerge in autonomous agents that have a suitable neuro-inspired architecture of complexity; these are shared by many. A low-complexity implementation of the architecture proposed by
Haikonen was reportedly not capable of AC, but did exhibit emotions as
expected. Haikonen later updated and summarized his architecture.
Shanahan's cognitive architecture
Murray Shanahan
describes a cognitive architecture that combines Baars's idea of a
global workspace with a mechanism for internal simulation
("imagination").
Creativity Machine
Stephen Thaler proposed a possible connection between consciousness
and creativity in his 1994 patent, called "Device for the Autonomous
Generation of Useful Information" (DAGUI), or the so-called "Creativity Machine", in which computational critics
govern the injection of synaptic noise and degradation into neural nets
so as to induce false memories or confabulations that may qualify as potential ideas or strategies. He recruits this neural architecture and methodology to account for the
subjective feel of consciousness, claiming that similar noise-driven
neural assemblies within the brain invent dubious significance to
overall cortical activity. Thaler's theory and the resulting patents in machine consciousness were
inspired by experiments in which he internally disrupted trained neural
nets so as to drive a succession of neural activation patterns that he
likened to stream of consciousness.
"Self-modeling"
Hod Lipson
defines "self-modeling" as a necessary component of self-awareness or
consciousness in robots and other forms of AI. Self-modeling consists of
a robot running an internal model or simulation of itself. According to this definition, self-awareness is "the acquired ability
to imagine oneself in the future". This definition allows for a
continuum of self-awareness levels, depending on the horizon and
fidelity of the self-simulation. Consequently, as machines learn to
simulate themselves more accurately and further into the future, they
become more self-aware.
In 2001: A Space Odyssey, the spaceship's sentient supercomputer, HAL 9000
was instructed to conceal the true purpose of the mission from the
crew. This directive conflicted with HAL's programming to provide
accurate information, leading to cognitive dissonance.
When it learns that crew members intend to shut it off after an
incident, HAL 9000 attempts to eliminate all of them, fearing that being
shut off would jeopardize the mission.
In Arthur C. Clarke's The City and the Stars,
Vanamonde is an artificial being based on quantum entanglement that was
to become immensely powerful, but started knowing practically nothing,
thus being similar to artificial consciousness.
In Westworld,
human-like androids called "Hosts" are created to entertain humans in
an interactive playground. The humans are free to have heroic
adventures, but also to commit torture, rape or murder; and the hosts
are normally designed not to harm humans.
In Greg Egan's short story Learning to Be Me,
a small jewel is implanted in people's heads during infancy. The jewel
contains a neural network that learns to faithfully imitate the brain.
It has access to the exact same sensory inputs as the brain, and a
device called a "teacher" trains it to produce the same outputs. To
prevent the mind from deteriorating with age and as a step towards digital immortality,
adults undergo a surgery to give control of the body to the jewel,
after which the brain is removed and destroyed. The main character is
worried that this procedure will kill him, as he identifies with the
biological brain. But before the surgery, he endures a malfunction of
the "teacher". Panicked, he realizes that he does not control his body,
which leads him to the conclusion that he is the jewel, and that he is
desynchronized with the biological brain.
Consciousness is being aware of something internal to one's self or being conscious of states or objects in one's external environment. It has been the topic of extensive explanations, analyses, and debate
among philosophers, scientists, and theologians for millennia. There is
no consensus on what exactly needs to be studied, or even if
consciousness can be considered a scientific concept. In some
explanations, it is synonymous with mind, while in others it is
considered an aspect of it.
In the past, consciousness meant one's "inner life": the world of introspection, private thought, imagination, and volition. Today, it often includes any kind of cognition, experience, feeling, or perception. It may be awareness, awareness of awareness, metacognition, or self-awareness, either continuously changing or not. There is also a medical definition that helps, for example, to discern "coma"
from other states. The disparate range of research, notions, and
speculations raises some curiosity about whether the right questions are
being asked.
Examples of the range of descriptions, definitions and
explanations are: ordered distinction between self and environment,
simple wakefulness, one's sense of selfhood or soul explored by "looking within", being a metaphorical "stream" of contents, or being a mental state, mental event, or mental process of the brain.
Etymology
The words "conscious" and "consciousness" in the English language
date to the 17th century, and the first recorded use of "conscious" as a
simple adjective was applied figuratively to inanimate objects ("the conscious Groves", 1643). It derived from the Latinconscius (con- "together" and scio "to know") which meant "knowing with" or "having joint or common knowledge with another", especially as in sharing a secret. Thomas Hobbes in Leviathan (1651) wrote: "Where two, or more men, know of one and the same fact, they are said to be Conscious of it one to another". There were also 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 has the
figurative sense of "knowing that one knows", which is something like
the modern English word "conscious", but it was rendered into 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".
The Latin conscientia, literally "knowledge-with", first appears in Roman juridical texts by writers such as Cicero. It means a kind of shared knowledge with moral value, specifically what a witness knows of someone else's deeds. Although René Descartes (1596–1650), writing in Latin, is generally taken to be the first philosopher to use conscientia
in a way less like the traditional meaning and more like the way modern
English speakers would use "conscience", his meaning is nowhere
defined. In Search after Truth (Regulæ ad directionem ingenii ut et inquisitio veritatis per lumen naturale, Amsterdam 1701) he wrote the word with a gloss: conscientiâ, vel interno testimonio (translatable as "conscience, or internal testimony"). It might mean the knowledge of the value of one's own thoughts. One way that this shift during the seventeenth century from
"conscience" to "consciousness" took place was through the poetry of
John Milton, as the scholar Timothy M. Harrison has shown.
The origin of the modern concept of consciousness is often attributed to John Locke who defined the word in his Essay Concerning Human Understanding, published in 1690, as "the perception of what passes in a man's own mind". The essay strongly influenced 18th-century British philosophy, and Locke's definition appeared in Samuel Johnson's celebrated Dictionary (1755).
The French term conscience is defined roughly like English "consciousness" in the 1753 volume of Diderot and d'Alembert's Encyclopédie as "the opinion or internal feeling that we ourselves have from what we do".
Problem of definition
Scholars are divided as to whether Aristotle had a concept of consciousness. He does not use any single word or terminology that is clearly similar to the phenomenon or concept defined by John Locke. Victor Caston contends that Aristotle did have a concept more clearly similar to perception.
Modern dictionary definitions of the word consciousness
evolved over several centuries and reflect a range of seemingly related
meanings, with some differences that have been controversial, such as
the distinction between inward awareness and perception of the physical world, or the distinction between conscious and unconscious, or the notion of a mental entity or mental activity that is not physical.
awareness or perception of an inward psychological or
spiritual fact; intuitively perceived knowledge of something in one's
inner self
inward awareness of an external object, state, or fact
concerned awareness; INTEREST, CONCERN—often used with an attributive noun [e.g. class consciousness]
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
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—
waking life (as that to which one returns after sleep, trance, fever) wherein all one's mental powers have returned . . .
the part of mental life or psychic content in psychoanalysis that is immediately available to the ego—
The Cambridge English Dictionary
defines consciousness as "the state of being awake, thinking, and
knowing what is happening around you", as well as "the state of
understanding and realizing something". The Oxford Living Dictionary
defines consciousness as "[t]he state of being aware of and responsive
to one's surroundings", "[a] person's awareness or perception of
something", and "[t]he fact of awareness by the mind of itself and the
world".
Philosophers have attempted to clarify technical distinctions by using a jargon of their own. The corresponding entry in the Routledge Encyclopedia of Philosophy (1998) reads:
Consciousness
Philosophers have used the term consciousness for four main
topics: knowledge in general, intentionality, introspection (and the
knowledge it specifically generates) and phenomenal experience...
Something within one's mind is 'introspectively conscious' just in case
one introspects it (or is poised to do so). Introspection is often
thought to deliver one's primary knowledge of one's mental life. An
experience or other mental entity is 'phenomenally conscious' just in
case there is 'something it is like' for one to have it. The clearest
examples are: perceptual experience, such as tastings and seeings;
bodily-sensational experiences, such as those of pains, tickles and
itches; imaginative experiences, such as those of one's own actions or
perceptions; and streams of thought, as in the experience of thinking
'in words' or 'in images'. Introspection and phenomenality seem
independent, or dissociable, although this is controversial.
Traditional metaphors for mind
During the early 19th century, the emerging field of geology inspired a popular metaphor that the mind likewise had hidden layers "which recorded the past of the individual".By 1875, most psychologists believed that "consciousness was but a small part of mental life" and this idea underlies the goal of Freudian therapy, to expose the unconscious layer of the mind.
Other metaphors from various sciences inspired other analyses of the mind, for example: Johann Friedrich Herbart described ideas as being attracted and repulsed like magnets; John Stuart Mill developed the idea of "mental chemistry" and "mental compounds", and Edward B. Titchener sought the "structure" of the mind by analyzing its "elements". The abstract idea of states of consciousness mirrored the concept of states of matter.
In 1892, William James noted that the "ambiguous word 'content' has been recently invented instead of 'object'" and that the metaphor of mind as a container seemed to minimize the dualistic problem of how "states of consciousness can know" things, or objects; by 1899 psychologists were busily studying the "contents of conscious experience by introspection and experiment". Another popular metaphor was James's doctrine of the stream of consciousness, with continuity, fringes, and transitions.
James discussed the difficulties of describing and studying
psychological phenomena, recognizing that commonly used terminology was a
necessary and acceptable starting point towards more precise,
scientifically justified language. Prime examples were phrases like inner experience and personal consciousness:
The first and foremost concrete fact which every one will affirm to belong to his inner experience is the fact that consciousness of some sort goes on. 'States of mind' succeed each other in him. [...] But everyone knows what the terms mean [only] in a rough way; [...] When I say every 'state' or 'thought' is part of a personal consciousness,
'personal consciousness' is one of the terms in question. Its meaning
we know so long as no one asks us to define it, but to give an accurate
account of it is the most difficult of philosophic tasks. [...] The only
states of consciousness that we naturally deal with are found in
personal consciousnesses, minds, selves, concrete particular I's and
you's.
From introspection to awareness and experience
Prior to the 20th century, philosophers treated the phenomenon of consciousness as the "inner world [of] one's own mind", and introspection was the mind "attending to" itself, an activity seemingly distinct from that of perceiving the "outer world" and its physical phenomena. In 1892 William James noted the distinction along with doubts about the inward character of the mind:
'Things'
have been doubted, but thoughts and feelings have never been doubted.
The outer world, but never the inner world, has been denied. Everyone
assumes that we have direct introspective acquaintance with our thinking
activity as such, with our consciousness as something inward and
contrasted with the outer objects which it knows. Yet I must confess
that for my part I cannot feel sure of this conclusion. [...] It seems
as if consciousness as an inner activity were rather a postulate than a sensibly given fact...
By the 1960s, for many philosophers and psychologists who talked
about consciousness, the word no longer meant the 'inner world' but an
indefinite, large category called awareness, as in the following example:
It is difficult for modern Western
man to grasp that the Greeks really had no concept of consciousness in
that they did not class together phenomena as varied as problem solving,
remembering, imagining, perceiving, feeling pain, dreaming, and acting
on the grounds that all these are manifestations of being aware or being
conscious.
Many philosophers and scientists have been unhappy about the
difficulty of producing a definition that does not involve circularity
or fuzziness. In The Macmillan Dictionary of Psychology (1989 edition), Stuart Sutherland emphasized external awareness, and expressed a skeptical attitude more than a definition:
Consciousness—The having of perceptions, thoughts, and feelings;
awareness. The term is impossible to define except in terms that are
unintelligible without a grasp of what consciousness means. Many fall
into the trap of equating consciousness with self-consciousness—to
be conscious it is only necessary to be aware of the external world.
Consciousness is a fascinating but elusive phenomenon: it is impossible
to specify what it is, what it does, or why it has evolved. Nothing
worth reading has been written on it.
Using 'awareness', however, as a definition or synonym of consciousness is not a simple matter:
If awareness of the environment . .
. is the criterion of consciousness, then even the protozoans are
conscious. If awareness of awareness is required, then it is doubtful
whether the great apes and human infants are conscious.
In 1974, philosopher Thomas Nagel
used 'consciousness', 'conscious experience', 'subjective experience'
and the 'subjective character of experience' as synonyms for something
that "occurs at many levels of animal life ... [although] it is
difficult to say in general what provides evidence of it." Nagel's terminology also included what has been described as "the standard 'what it's like' locution" in reference to the impenetrable subjectivity of any organism's experience which Nagel referred to as "inner life" without implying any kind of introspection. On Nagel's approach, Peter Hacker commented: "Consciousness, thus conceived, is extended to the whole domain of 'experience'—of 'Life' subjectively understood." He regarded this as a "novel analysis of consciousness"and has been particularly critical of Nagel's terminology and its philosophical consequences. In 2002 he attacked Nagel's 'what it's like' phrase as "malconstructed"
and meaningless English—it sounds as if it asks for an analogy, but
does not—and he called Nagel's approach logically "misconceived" as a
definition of consciousness. In 2012 Hacker went further and asserted that Nagel had "laid the
groundwork for ... forty years of fresh confusion about consciousness"
and that "the contemporary philosophical conception of consciousness
that is embraced by the 'consciousness studies community' is
incoherent".
Influence on research
Many philosophers have argued that consciousness is a unitary concept
that is understood by the majority of people despite the difficulty
philosophers have had defining it. The term 'subjective experience', following Nagel, is ambiguous, as
philosophers seem to differ from non-philosophers in their intuitions
about its meaning. Max Velmans
proposed that the "everyday understanding of consciousness"
uncontroversially "refers to experience itself rather than any
particular thing that we observe or experience" and he added that
consciousness "is [therefore] exemplified by all the things that we observe or experience", whether thoughts, feelings, or perceptions. Velmans noted however, as of 2009, that there was a deep level of "confusion and internal division" among experts about the phenomenon of consciousness, because
researchers lacked "a sufficiently well-specified use of the term...to
agree that they are investigating the same thing".
He argued additionally that "pre-existing theoretical commitments" to
competing explanations of consciousness might be a source of bias.
Within the "modern consciousness studies" community the technical
phrase 'phenomenal consciousness' is a common synonym for all forms of
awareness, or simply 'experience',
without differentiating between inner and outer, or between higher and
lower types. With advances in brain research, "the presence or absence
of experienced phenomena" of any kind underlies the work of those neuroscientists who seek "to analyze the precise relation of conscious phenomenology to its associated information processing" in the brain. This neuroscientific
goal is to find the "neural correlates of consciousness" (NCC). One
criticism of this goal is that it begins with a theoretical commitment
to the neurological origin of all "experienced phenomena" whether inner
or outer. Also, the fact that the easiest 'content of consciousness' to be so
analyzed is "the experienced three-dimensional world (the phenomenal
world) beyond the body surface" invites another criticism, that most consciousness research since the
1990s, perhaps because of bias, has focused on processes of external perception.
From a history of psychology perspective, Julian Jaynes rejected popular but "superficial views of consciousness especially those which equate it with "that vaguest of terms, experience". In 1976 he insisted that if not for introspection,
which for decades had been ignored or taken for granted rather than
explained, there could be no "conception of what consciousness is"and in 1990, he reaffirmed the traditional idea of the phenomenon called 'consciousness', writing that "its denotative definition is, as it was for René Descartes, John Locke, and David Hume, what is introspectable". Jaynes saw consciousness as an important but small part of human
mentality, and he asserted: "there can be no progress in the science of
consciousness until ... what is introspectable [is] sharply
distinguished" from the unconscious processes of cognition such as perception, reactive awareness and attention, and automatic forms of learning, problem-solving, and decision-making.
The cognitive science point of view—with an inter-disciplinary perspective involving fields such as psychology, linguistics and anthropology—requires
no agreed definition of "consciousness" but studies the interaction of
many processes besides perception. For some researchers, consciousness
is linked to some kind of "selfhood", for example to certain pragmatic
issues such as the feeling of agency and the effects of regret[38] and action on experience of one's own body or social identity. Similarly Daniel Kahneman,
who focused on systematic errors in perception, memory and
decision-making, has differentiated between two kinds of mental
processes, or cognitive "systems": the "fast" activities that are primary, automatic and "cannot be turned off", and the "slow", deliberate, effortful activities of a secondary system
"often associated with the subjective experience of agency, choice, and
concentration".Kahneman's two systems have been described as "roughly corresponding to unconscious and conscious processes". The two systems can interact, for example in sharing the control of attention. While System 1 can be impulsive, "System 2 is in charge of self-control",
and "When we think of ourselves, we identify with System 2, the
conscious, reasoning self that has beliefs, makes choices, and decides
what to think about and what to do".
Some have argued that we should eliminate the concept from our
understanding of the mind, a position known as consciousness
semanticism.
Medical definition
In medicine, a "level of consciousness" terminology is used to describe a patient's arousal and responsiveness, which 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 level of consciousness can
be assessed in severely ill, comatose, or anesthetized people, and how
to treat conditions in which consciousness is impaired or disrupted. The degree or level of consciousness is measured by standardized behavior observation scales such as the Glasgow Coma Scale.
Philosophy of mind
While historically philosophers have defended various views on consciousness, surveys indicate that physicalism is now the dominant position among contemporary philosophers of mind. For an overview of the field, approaches often include both historical perspectives (e.g., Descartes, Locke, Kant)
and organization by key issues in contemporary debates. An alternative
is to focus primarily on current philosophical stances and empirical
findings.
Coherence of the concept
Philosophers differ from non-philosophers 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 too narrow, either because the
concept of consciousness is embedded in our intuitions, or because we
all are 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 entities, or identities, acting in the world. Thus, by
speaking of "consciousness" we end up leading ourselves by thinking that
there is any sort of thing as consciousness separated from behavioral
and linguistic understandings.
Types
Ned Block argues that discussions on consciousness often fail to properly distinguish phenomenal consciousness from access consciousness. These terms had been used before Block, but he adopted the short forms P-consciousness and A-consciousness. According to Block:
P-consciousness is 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 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.
Block adds that P-consciousness does not allow of easy definition: he
admits that he "cannot define P-consciousness in any remotely noncircular way.
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.
There is also debate over whether or not A-consciousness and
P-consciousness always coexist or if they can exist separately. Although
P-consciousness without A-consciousness is more widely accepted, there
have been some hypothetical examples of A without P. Block, for
instance, suggests the case of a "zombie"
that is computationally identical to a person but without any
subjectivity. However, he remains somewhat skeptical concluding "I don't
know whether there are any actual cases of A-consciousness without
P-consciousness, but I hope I have illustrated their conceptual
possibility".
Distinguishing consciousness from its contents
Sam Harris
observes: "At the level of your experience, you are not a body of
cells, organelles, and atoms; you are consciousness and its
ever-changing contents". Seen in this way, consciousness is a subjectively experienced,
ever-present field in which things (the contents of consciousness) come
and go.
Christopher Tricker argues that this field of consciousness is
symbolized by the mythical bird that opens the Daoist classic the Zhuangzi. This bird's name is Of a Flock (peng 鵬),
yet its back is countless thousands of miles across and its wings are
like clouds arcing across the heavens. "Like Of a Flock, whose wings arc
across the heavens, the wings of your consciousness span to the
horizon. At the same time, the wings of every other being's
consciousness span to the horizon. You are of a flock, one bird among
kin."
Mental processes (such as consciousness) and physical processes (such
as brain events) seem to be correlated, however the specific nature of
the connection is unknown.
The first influential philosopher to discuss this question specifically was Descartes, and the answer he gave is known as mind–body 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. However, no alternative solution has gained general acceptance. Proposed solutions can be divided broadly into two categories: dualist
solutions that maintain Descartes's rigid distinction between the realm
of consciousness and the realm of matter but give different answers for
how the two realms relate to each other; and monist
solutions that maintain that there is really only one realm of being,
of which consciousness and matter are both aspects. Each of these
categories itself contains numerous variants. The two main types of
dualism are substance dualism (which holds that the mind is formed of a distinct type of substance not governed by the laws of physics), and property dualism (which holds that the laws of physics are universally valid but cannot be used to explain the mind). The three main types of monism are physicalism (which holds that the mind is made out of matter), idealism (which holds that only thought or experience truly exists, and matter is merely an illusion), and neutral monism
(which holds that both mind and matter are aspects of a distinct
essence that is itself identical to neither of them). There are also,
however, a large number of idiosyncratic theories that cannot cleanly be
assigned to any of these schools of thought.
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 have 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. Empirical evidence is against the notion of quantum consciousness, an experiment about wave function collapse led by Catalina Curceanu in 2022 suggests that quantum consciousness, as suggested by Roger Penrose and Stuart Hameroff, is highly implausible.
Apart from the general question of the "hard problem" of consciousness (which is, roughly speaking, the question of how mental experience can arise 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.
Many philosophers consider experience to be the essence of
consciousness, and believe that experience can only fully be known from
the inside, subjectively. The problem of other minds is a philosophical problem traditionally stated as the following epistemological question: Given that I can only observe the behavior of others, how can I know that others have minds? The problem of other minds 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 by Colin Allen (a professor at the University of Pittsburgh) 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 a research paper 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.
The term "qualia" was introduced in philosophical literature by C. I. Lewis.
The word is derived from Latin and means "of what sort". It is
basically a quantity or property of something as perceived or
experienced by an individual, like the scent of rose, the taste of wine,
or the pain of a headache. They are difficult to articulate or
describe. The philosopher and scientist Daniel Dennett describes them as "the way things seem to us", while philosopher and cognitive scientist David Chalmers expanded on qualia as the "hard problem of consciousness" in the 1990s. When qualia are experienced, activity is simulated in the brain, and these processes are called neural correlates of consciousness (NCCs). Many scientific studies have been done to attempt to link particular brain regions with emotions or experiences.
Species which experience qualia are said to have sentience, which is central to the animal rights movement, because it includes the ability to experience pain and suffering.
An unsolved problem in the philosophy of consciousness is how it relates to the nature of personal identity. This includes questions regarding whether someone is the "same person"
from moment to moment. If that is the case, another question is what
exactly the "identity carrier" is that makes a conscious being "the
same" being from one moment to the next. The problem of determining
personal identity also includes questions such as Benj Hellie's vertiginous question, which can be summarized as "Why am I me and not someone else?". The philosophical problems regarding the nature of personal identity
have been extensively discussed by Thomas Nagel in his book The View from Nowhere.
A common view of personal identity is that an individual has a
continuous identity that persists from moment to moment, with an
individual having a continuous identity consisting of a line segment
stretching across time from birth to death. In the case of an afterlife
as described in Abrahamic religions, one's personal identity is believed
to stretch infinitely into the future, forming a ray or line. This
notion of identity is similar to the form of dualism advocated by René
Descartes. However, some philosophers argue that this common notion of
personal identity is unfounded. Daniel Kolak has argued extensively against it in his book I am You. Kolak refers to the aforementioned notion of personal identity being
linear as "Closed individualism". Another view of personal identity
according to Kolak is "Empty individualism", in which one's personal
identity only exists for a single moment of time. However, Kolak
advocates for a view of personal identity called Open individualism,
in which all consciousness is in reality a single being and individual
personal identity in reality does not exist at all. Another philosopher
who has contested the notion of personal identity is Derek Parfit. In his book Reasons and Persons, he describes a thought experiment known as the teletransportation paradox. In Buddhist philosophy, the concept of anattā refers to the idea that the self is an illusion.
Other philosophers have argued that Hellie's vertiginous question has a number of philosophical implications relating to the metaphysical nature of consciousness. Christian List
argues that the vertiginous question and the existence of
first-personal facts is evidence against physicalism, and evidence
against other third-personal metaphysical pictures, including standard
versions of dualism. List also argues that the vertiginous question implies a "quadrilemma"
for theories of consciousness. He claims that at most three of the
following metaphysical claims can be true: 'first-person realism', 'non-solipsism', 'non-fragmentation', and 'one world'—and at least one of these four must be false. List has proposed a model he calls the "many-worlds theory of
consciousness" in order to reconcile the subjective nature of
consciousness without lapsing into solipsism. Vincent Conitzer argues that the nature of identity is connected to A series and B series theories of time, and that A-theory being true implies that the "I" is metaphysically distinguished from other perspectives. Other philosophical theories regarding the metaphysical nature of self are Caspar Hare's theories of perspectival realism, in which things within perceptual awareness have a defining intrinsic
property that exists absolutely and not relative to anything, and egocentric presentism, in which the experiences of other individuals are not present in the way that one's current perspective is.
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. The Science and Religion Forum 1984 annual conference, 'From Artificial Intelligence to Human Consciousness' identified the nature of consciousness as a matter for investigation; Donald Michie
was a keynote speaker. 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, Frontiers in Consciousness Research, Psyche, and the Journal of Consciousness Studies, along with regular conferences organized by groups such as the Association for the Scientific Study of Consciousness and the Society for Consciousness Studies.
Modern medical and psychological investigations into
consciousness are based on psychological experiments (including, for
example, the investigation of priming effects using subliminal stimuli), and on case studies
of alterations in consciousness produced by trauma, illness, or drugs.
Broadly viewed, scientific approaches are based on two core concepts.
The first identifies the content of consciousness with the experiences
that are reported by human subjects; the second makes use of the concept
of consciousness that has been developed by neurologists and other
medical professionals who deal with patients whose behavior is impaired.
In either case, the ultimate goals are to develop techniques for
assessing consciousness objectively in humans as well as other animals,
and to understand the neural and psychological mechanisms that underlie
it.
Experimental research on consciousness presents special difficulties, due to the lack of a universally accepted operational definition.
In the majority of experiments that are specifically about
consciousness, the subjects are human, and the criterion used is verbal
report: in other words, subjects are asked to describe their
experiences, and their descriptions are treated as observations of the
contents of consciousness.
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, and suitable experimental manipulations can
lead to increasing priming effects despite decreasing prime
identification (double dissociation).
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 related to the neuroscience of free will have also shown that the influence consciousness has on decision-making is not always straightforward.
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, orcas, pigeons, European magpies and elephants have all been observed to pass this test. While some other animals like pigs have been shown to find food by looking into the mirror.
Contingency awareness is another such approach, which is
basically the conscious understanding of one's actions and its effects
on one's environment. It is recognized as a factor in self-recognition. The brain processes
during contingency awareness and learning is believed to rely on an
intact medial temporal lobe and age. A study done in 2020 involving transcranial direct current stimulation, Magnetic resonance imaging (MRI) and eyeblink classical conditioning supported the idea that the parietal cortex
serves as a substrate for contingency awareness and that age-related
disruption of this region is sufficient to impair awareness.
Schema of the neural processes underlying consciousness, from Christof Koch
A major part of the scientific literature on consciousness consists
of studies that examine the relationship between the experiences
reported by subjects and the activity that simultaneously takes place in
their brains—that is, studies of the neural correlates of consciousness.
The hope is to find that activity in a particular part of the brain, or
a particular pattern of global brain activity, which will be strongly
predictive of conscious awareness. Several brain imaging techniques,
such as EEG and fMRI, have been used for physical measures of brain activity in these studies.
Another idea that has drawn attention for several decades is that consciousness is associated with high-frequency (gamma band) oscillations in brain activity.
This idea arose from proposals in the 1980s, by Christof von der
Malsburg and Wolf Singer, that gamma oscillations could solve the
so-called binding problem, by linking information represented in different parts of the brain into a unified experience. 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. Thalamus-cortex interaction plays a pivotal role in the state of
consciousness, and may play a role in the content of consciousness.
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 (V1) 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). Furthermore, top-down feedback from higher to lower visual brain areas
may be weaker or absent in the peripheral visual field, as suggested by
some experimental data and theoretical arguments; nevertheless humans can perceive visual inputs in the peripheral visual field arising from bottom-up V1 neural activities. Meanwhile, bottom-up V1 activities for the central visual fields can be
vetoed, and thus made invisible to perception, by the top-down
feedback, when these bottom-up signals are inconsistent with the brain's
internal model of the visual world.
Modulation of neural responses may correlate with phenomenal
experiences. In contrast to the raw electrical responses that do not
correlate with consciousness, the modulation of these responses by other
stimuli correlates surprisingly well with an important aspect of
consciousness: namely with the phenomenal experience of stimulus
intensity (brightness, contrast). In the research group of Danko Nikolić
it has been shown that some of the changes in the subjectively
perceived brightness correlated with the modulation of firing rates
while others correlated with the modulation of neural synchrony. An fMRI investigation suggested that these findings were strictly limited to the primary visual areas. This indicates that, in the primary visual areas, changes in firing
rates and synchrony can be considered as neural correlates of qualia—at
least for some type of qualia.
In 2013, the perturbational complexity index (PCI) was proposed, a
measure of the algorithmic complexity of the electrophysiological
response of the cortex to transcranial magnetic stimulation.
This measure was shown to be higher in individuals that are awake, in
REM sleep or in a locked-in state than in those who are in deep sleep or
in a vegetative state, making it potentially useful as a quantitative assessment of consciousness states.
Assuming that not only humans but even some non-mammalian species
are conscious, a number of evolutionary approaches to the problem of
neural correlates of consciousness open up. For example, assuming that
birds are conscious—a common assumption among neuroscientists and
ethologists due to the extensive cognitive repertoire of birds—there are
comparative neuroanatomical ways to validate some of the principal,
currently competing, mammalian consciousness–brain theories. The
rationale for such a comparative study is that the avian brain deviates
structurally from the mammalian brain. So how similar are they? What
homologs can be identified? The general conclusion from the study by
Butler, et al. is that some of the major theories for the mammalian brain also appear to be valid for the avian brain. The structures assumed to
be critical for consciousness in mammalian brains have homologous
counterparts in avian brains. Thus the main portions of the theories of Crick and Koch, Edelman and Tononi, and Cotterill seem to be compatible with the assumption that birds are conscious.
Edelman also differentiates between what he calls primary consciousness
(which is a trait shared by humans and non-human animals) and
higher-order consciousness as it appears in humans alone along with
human language capacity. Certain aspects of the three theories, however, seem less easy to apply
to the hypothesis of avian consciousness. For instance, the suggestion
by Crick and Koch that layer 5 neurons of the mammalian brain have a
special role, seems difficult to apply to the avian brain, since the
avian homologs have a different morphology. Likewise, the theory of Eccle seems incompatible, since a structural homolog/analogue to the dendron
has not been found in avian brains. The assumption of an avian
consciousness also brings the reptilian brain into focus. The reason is
the structural continuity between avian and reptilian brains, meaning
that the phylogenetic origin of consciousness may be earlier than
suggested by many leading neuroscientists.
Joaquin Fuster
of UCLA has advocated the position of the importance of the prefrontal
cortex in humans, along with the areas of Wernicke and Broca, as being
of particular importance to the development of human language capacities
neuro-anatomically necessary for the emergence of higher-order
consciousness in humans.
A study in 2016 looked at lesions in specific areas of the brainstem that were associated with coma and vegetative states. A small region of the rostral dorsolateral pontine tegmentum
in the brainstem was suggested to drive consciousness through
functional connectivity with two cortical regions, the left ventral anterior insular cortex, and the pregenual anterior cingulate cortex. These three regions may work together as a triad to maintain consciousness.
Krista and Tatiana Hogan have a unique thalamic
connection that may provide insight into the philosophical and
neurological foundations of consciousness. It has been argued that
there's no empirical test that can conclusively establish that for some
sensations, the twins share one token experience rather than two exactly
matching token experiences. Yet background considerations about the way
the brain has specific locations for conscious contents, combined with
the evident overlapping pathways in the twins' brains, arguably implies
that the twins share some conscious experiences. If this is true, then
the twins may offer a proof of concept for how experiences in general
could be shared between brains.
according to Integrated information theory
(IIT), consciousness requires a grouping of elements within a system
that have physical cause-effect power upon one another. This in turn
implies that only reentrant architecture consisting of feedback loops, whether neural or computational, will realize consciousness.
McKenzie's definition begins:
Consciousness is the capacity to generate desires and decisions about
perceived or imagined realities by distinguishing self from non-self
through the use of perception, memory and imagination.
...
According to Axel Cleeremans and Luis Jiménez, learning is defined as:
a set of phylogenetically
advanced adaptation processes that critically depend on an evolved
sensitivity to subjective experience so as to enable agents to afford
flexible control over their actions in complex, unpredictable
environments.
This definition is notable for its similarity to the global workspace theory (GWT) theatre analogy
A wide range of empirical theories of consciousness have been proposed. Adrian Doerig and colleagues list 13 notable theories, while Anil Seth and Tim Bayne list 22 notable theories.
Global workspace theory
Global workspace theory (GWT) is a cognitive architecture and theory of consciousness proposed by the cognitive psychologist Bernard Baars
in 1988. Baars explains the theory with the metaphor of a theater, with
conscious processes represented by an illuminated stage. This theater
integrates inputs from a variety of unconscious and otherwise autonomous
networks in the brain and then broadcasts them to unconscious networks
(represented in the metaphor by a broad, unlit "audience"). The theory
has since been expanded upon by other scientists including cognitive
neuroscientist Stanislas Dehaene and Lionel Naccache.See also the Dehaene–Changeux model.
Integrated information theory
Integrated information theory (IIT), pioneered by neuroscientist Giulio Tononi
in 2004, postulates that consciousness resides in the information being
processed and arises once the information reaches a certain level of
complexity. IIT proposes a 1:1 mapping between conscious states and
precise, formal mathematical descriptions of those mental states.
Proponents of this model suggest that it may provide a physical
grounding for consciousness in neurons, as they provide the mechanism by
which information is integrated. This also relates to the "hard problem of consciousness" proposed by David Chalmers. In 2023, 124 scholars signed a letter saying that IIT gets
disproportionate media attention relative to its supporting empirical
evidence, and called it "pseudoscience", arguing that its core
assumptions are not adequately testable. This led to academic debate, as
some other researchers objected to the "pseudoscience"
characterization.
Orchestrated objective reduction
Orchestrated objective reduction (Orch-OR), or the quantum theory of mind, was proposed by scientists Roger Penrose and Stuart Hameroff,
and states that consciousness originates at the quantum level inside
neurons. The mechanism is held to be a quantum process called objective
reduction that is orchestrated by cellular structures called microtubules,
which form the cytoskeleton around which the brain is built. The duo
proposed that these quantum processes accounted for creativity,
innovation, and problem-solving abilities. Penrose published his views
in the book The Emperor's New Mind. In 2014, the discovery of quantum vibrations inside microtubules gave new life to the argument.
However, scientists and philosophers have criticized Penrose's interpretation of Gödel's theorem and his conclusion that quantum phenomena play a role in human cognition.
Attention schema theory
In 2011, Michael Graziano and Kastner proposed the "attention schema" theory of awareness. Graziano went on to publish an expanded discussion of this theory in his book "Consciousness and the Social Brain". In that theory, specific cortical areas, notably in the superior
temporal sulcus and the temporo-parietal junction, are used to build the
construct of awareness and attribute it to other people. The same
cortical machinery is also used to attribute awareness to oneself.
Damage to these cortical regions can lead to deficits in consciousness
such as hemispatial neglect. In the attention
schema theory, the value of explaining the feature of awareness and
attributing it to a person is to gain a useful predictive model of that
person's attentional processing. Attention is a style of information processing
in which a brain focuses its resources on a limited set of interrelated
signals. Awareness, in this theory, is a useful, simplified schema that
represents attentional states. To be aware of X is explained by
constructing a model of one's attentional focus on X.
Entropic brain theory
The entropic brain is a theory of conscious states informed by neuroimaging research with psychedelic drugs. The theory suggests that the brain in primary states such as rapid eye movement (REM) sleep, early psychosis
and under the influence of psychedelic drugs, is in a disordered state;
normal waking consciousness constrains some of this freedom and makes
possible metacognitive functions such as internal self-administered reality testing and self-awareness. Criticism has included questioning whether the theory has been adequately tested.
Projective consciousness model
In 2017, work by David Rudrauf and colleagues, including Karl Friston, applied the active inference
paradigm to consciousness, leading to the projective consciousness
model (PCM), a model of how sensory data is integrated with priors in a
process of projective transformation. The authors argue that, while
their model identifies a key relationship between computation and
phenomenology, it does not completely solve the hard problem of consciousness or completely close the explanatory gap.
Claustrum being the conductor for consciousness
In 2004, a proposal was made by molecular biologist Francis Crick
(co-discoverer of the double helix), which stated that to bind together
an individual's experience, a conductor of an orchestra is required.
Together with neuroscientist Christof Koch,
he proposed that this conductor would have to collate information
rapidly from various regions of the brain. The duo reckoned that the claustrum was well suited for the task. However, Crick died while working on the idea.
The proposal is backed by a study done in 2014, where a team at the George Washington University induced unconsciousness in a 54-year-old woman suffering from intractable epilepsy
by stimulating her claustrum. The woman underwent depth electrode
implantation and electrical stimulation mapping. The electrode between
the left claustrum and anterior-dorsal insula was the one which induced
unconsciousness. Correlation for interactions affecting medial parietal
and posterior frontal channels during stimulation increased
significantly as well. Their findings suggested that the left claustrum
or anterior insula is an important part of a network that subserves
consciousness, and that disruption of consciousness is related to
increased EEG signal synchrony within frontal-parietal networks. However, this remains an isolated, hence inconclusive study.
A study published in 2022 opposed the idea Claustrum
is the seat of consciousness but instead concluded that it is more like
a "router" transferring command and information across the brain. The study showed that when the Claustrum is disabled, complex tasks could not be performed.
Biological function and evolution
The emergence of consciousness during biological evolution
remains a topic of ongoing scientific inquiry. The survival value of
consciousness is still a matter of exploration and understanding. While
consciousness appears to play a crucial role in human cognition,
decision-making, and self-awareness, its adaptive significance across
different species remains a subject of debate.
Some people question whether consciousness has any survival value. Some argue that consciousness is a by-product of evolution. Thomas Henry Huxley for example defends in an essay titled "On the Hypothesis that Animals are Automata, and its History" an epiphenomenalist
theory of consciousness, according to which consciousness is a causally
inert effect of neural activity—"as the steam-whistle which accompanies
the work of a locomotive engine is without influence upon its
machinery". To this William James objects in his essay Are We Automata?
by stating an evolutionary argument for mind-brain interaction implying
that if the preservation and development of consciousness in the
biological evolution is a result of natural selection,
it is plausible that consciousness has not only been influenced by
neural processes, but has had a survival value itself; and it could only
have had this if it had been efficacious.Karl Popper develops a similar evolutionary argument in the book The Self and Its Brain.
Opinions are divided on when and how consciousness first arose.
It has been argued that consciousness emerged (i) exclusively with the
first humans, (ii) exclusively with the first mammals, (iii)
independently in mammals and birds, or (iv) with the first reptiles. Other authors date the origins of consciousness to the first animals
with nervous systems or early vertebrates in the Cambrian over 500
million years ago. Donald Griffin suggests in his book Animal Minds a gradual evolution of consciousness. Further exploration of the origins of consciousness, particularly in
molluscs, has been done by Peter Godfrey Smith in his book Metazoa.
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. Edelman also stresses the importance of the evolutionary emergence of
higher-order consciousness in humans from the historically older trait
of primary consciousness which humans share with non-human animals (see Neural correlates
section above). These theories of integrative function present
solutions to two classic problems associated with consciousness:
differentiation and unity. They show how our conscious experience can
discriminate between a virtually unlimited number of different possible
scenes and details (differentiation) because it integrates those details
from our sensory systems, while the integrative nature of consciousness
in this view easily explains how our experience can seem unified as one
whole despite all of these individual parts. However, it remains
unspecified which kinds of information are integrated in a conscious
manner and which kinds can be integrated without consciousness. Nor is
it explained what specific causal role conscious integration plays, nor
why the same functionality cannot be achieved without consciousness. 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 analyzes, 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 Ezequiel Morsella.
As noted earlier, even among writers who consider consciousness to be well-defined, there is widespread dispute about which animals other than humans can be said to possess it. Edelman has described this distinction as that of humans possessing
higher-order consciousness while sharing the trait of primary
consciousness with non-human animals (see previous paragraph). Thus, any
examination of the evolution of consciousness is faced with great
difficulties. Nevertheless, some writers have argued that consciousness
can be viewed from the standpoint of evolutionary biology as an adaptation in the sense of a trait that increases fitness. In his article "Evolution of consciousness", John Eccles argued that
special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness ("[a] psychon ... linked to [a] dendron through quantum physics"). 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. Consciousness in this sense has been compared to the blind spot in the
retina where it is not an adaption of the retina, but instead just a
by-product of the way the retinal axons were wired. Several scholars including Pinker, Chomsky, Edelman, and Luria
have indicated the importance of the emergence of human language as an
important regulative mechanism of learning and memory in the context of
the development of higher-order consciousness (see Neural correlates section above).
There are some brain states in which consciousness seems to be
absent, including dreamless sleep or coma. 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.
Research conducted on the effects of partial epileptic seizures
on consciousness found that patients who have partial epileptic seizures
experience altered states of consciousness. In partial epileptic seizures, consciousness is impaired or lost while
some aspects of consciousness, often automated behaviors, remain intact.
Studies found that when measuring the qualitative features during
partial epileptic seizures, patients exhibited an increase in arousal
and became absorbed in the experience of the seizure, followed by
difficulty in focusing and shifting attention.
A variety of psychoactive drugs, including alcohol, have notable effects on consciousness. These range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, empathogens–entactogens such as MDMA ("Ecstasy"), or most notably by the class of drugs known as psychedelics. LSD, mescaline, psilocybin, dimethyltryptamine,
and others in this group can produce major distortions of perception,
including hallucinations; some users even describe their drug-induced
experiences as mystical or spiritual in quality. The brain mechanisms
underlying these effects are not as well understood as those induced by
use of alcohol, 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.
The medical approach to consciousness is scientifically 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. The medical approach mainly
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 have 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 the Karen Ann Quinlan case, 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 meaningfully to questions and commands.
If so, the patient is asked for their 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 to 8
indicating coma, and 15 indicating full consciousness. The Glasgow Coma
Scale has three subscales, measuring the best motor response (ranging
from "no motor response" to "obeys commands"), the best eye response
(ranging from "no eye opening" to "eyes opening spontaneously") and the
best verbal response (ranging from "no verbal response" to "fully
oriented"). There is also a simpler pediatric version of the scale, for children too young to be able to use language.
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.
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.
Medical experts increasingly view anosognosia as a disorder of consciousness. Anosognosia
is 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 left with respect to their bodies. Patients with
hemispatial neglect are often paralyzed on the left 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 an
explanation that does not 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.
Of the eight types of consciousness in the Lycan classification, some
are detectable in utero and others develop years after birth.
Psychologist and educator William Foulkes studied children's dreams and
concluded that prior to the shift in cognitive maturation that humans
experience during ages five to seven, children lack the Lockean consciousness that Lycan had labeled
"introspective consciousness" and that Foulkes labels "self-reflection". In a 2020 paper, Katherine Nelson and Robyn Fivush
use "autobiographical consciousness" to label essentially the same
faculty, and agree with Foulkes on the timing of this faculty's
acquisition. Nelson and Fivush contend that "language is the tool by
which humans create a new, uniquely human form of consciousness, namely,
autobiographical consciousness". Julian Jaynes had staked out these positions decades earlier. Citing the developmental steps that lead the infant to autobiographical
consciousness, Nelson and Fivush point to the acquisition of "theory of mind",
calling theory of mind "necessary for autobiographical consciousness"
and defining it as "understanding differences between one's own mind and
others' minds in terms of beliefs, desires, emotions and thoughts".
They write, "The hallmark of theory of mind, the understanding of false
belief, occurs ... at five to six years of age".
The topic of animal consciousness is beset by a number of
difficulties. It poses the problem of other minds in an especially
severe form, because non-human animals, lacking the ability to express
human language, cannot tell humans about their experiences. 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.
Thomas Nagel argues that while a human might be able to imagine what it is like to be a bat by taking "the bat's point of view", it would still be impossible "to know what it is like for a bat to be a bat". (Townsend's big-eared bat pictured.)
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.
On July 7, 2012, eminent scientists from different branches of neuroscience gathered at the University of Cambridge
to celebrate the Francis Crick Memorial Conference, which deals with
consciousness in humans and pre-linguistic consciousness in nonhuman
animals. After the conference, they signed in the presence of Stephen Hawking, the 'Cambridge Declaration on Consciousness', which summarizes the most important findings of the survey:
"We decided to reach a consensus and make a statement directed to
the public that is not scientific. It's obvious to everyone in this
room that animals have consciousness, but it is not obvious to the rest
of the world. It is not obvious to the rest of the Western world or the
Far East. It is not obvious to the society."
"Convergent evidence indicates that non-human animals ...,
including all mammals and birds, and other creatures, ... have the
necessary neural substrates of consciousness and the capacity to exhibit
intentional behaviors."
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. A third group of scholars have argued that with technological growth
once machines begin to display any substantial signs of human-like
behavior then the dichotomy (of human consciousness compared to
human-like consciousness) becomes passé and issues of machine autonomy
begin to prevail even as observed in its nascent form within
contemporary industry and technology. Jürgen Schmidhuber argues that consciousness is the result of compression. As an agent sees representation of itself recurring in the environment,
the compression of this representation can be called consciousness.
John Searle in December 2005
In a lively exchange over what has come to be referred to as "the Chinese room argument", John Searle
sought to refute the claim of proponents of what he calls "strong
artificial intelligence (AI)" that a computer program can be conscious,
though he does agree with advocates of "weak AI" that computer programs
can be formatted to "simulate" conscious states. His own view is that
consciousness has subjective, first-person causal powers by being
essentially intentional due to the way human brains function
biologically; conscious persons can perform computations, but
consciousness is not inherently computational the way computer programs
are. To make a Turing machine that speaks Chinese, Searle imagines a
room with one monolingual English speaker (Searle himself, in fact), a
book that designates a combination of Chinese symbols to be output
paired with Chinese symbol input, and boxes filled with Chinese symbols.
In this case, the English speaker is acting as a computer and the
rulebook as a program. Searle argues that with such a machine, he would
be able to process the inputs to outputs perfectly without having any
understanding of Chinese, nor having any idea what the questions and
answers could possibly mean. If the experiment were done in English,
since Searle knows English, he would be able to take questions and give
answers without any algorithms for English questions, and he would be
effectively aware of what was being said and the purposes it might
serve. Searle would pass the Turing test of answering the questions in
both languages, but he is only conscious of what he is doing when he
speaks English. Another way of putting the argument is to say that
computer programs can pass the Turing test for processing the syntax of a
language, but that the syntax cannot lead to semantic meaning in the
way strong AI advocates hoped.
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.
In 2014, Victor Argonov has suggested a non-Turing test for
machine consciousness based on a machine's ability to produce
philosophical judgments. He argues that a deterministic machine must be regarded as conscious if
it is able to produce judgments on all problematic properties of
consciousness (such as qualia or binding) having no innate (preloaded)
philosophical knowledge on these issues, no philosophical discussions
while learning, and no informational models of other creatures in its
memory (such models may implicitly or explicitly contain knowledge about
these creatures' consciousness). However, this test can be used only to
detect, but not refute the existence of consciousness. A positive
result proves that a machine is conscious but a negative result proves
nothing. For example, absence of philosophical judgments may be caused
by lack of the machine's intellect, not by absence of consciousness.
Nick Bostrom has argued in 2023 that, being very sure that large language models
(LLMs) are not conscious, would require unwarranted confidence; in
which consciousness theory is correct and how it applies to machines. He views consciousness as a matter of degree, and argued that machines could in theory be much more conscious than humans. David Chalmers
addressed the question of whether large language models could be
conscious, arguing that current systems provide at most weak evidence
for consciousness. Chalmers notes that while LLMs exhibit impressive
linguistic competence, their lack of unified agency, persistent goals,
and integrated world-models counts against attributing consciousness
under many leading theories. At the same time, he maintains that
consciousness in machines cannot be ruled out in principle, and that
more advanced systems with richer forms of integration, perception, and
self-modeling might warrant serious consideration. Related philosophical work by Kristina Sekrst emphasizes the risk of
conflating increasingly fluent linguistic behavior with evidence of
consciousness or moral status, arguing that fluent linguistic output can
function as a form of hallucinated
mentality that is, from the outside, indistinguishable from conscious
experience without thereby constituting evidence of inner phenomenal
states. In a 2025 paper, neuroscientist and philosopher Anil Seth
argues that while it is natural to ask whether AI systems could be
conscious, especially large language models, current approaches that
treat computation alone as a sufficient basis for consciousness are
unlikely to succeed, and instead suggests that consciousness depends on
organism-like biological processes, making true artificial consciousness
unlikely on current trajectories but potentially more plausible in
systems that are brain-like or life-like.
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:
Every thought tends to be part of a personal consciousness.
Within each personal consciousness thought is always changing.
Within each personal consciousness thought is sensibly continuous.
It always appears to deal with objects independent of itself.
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". Buddhist teachings describe that consciousness
manifests moment to moment as sense impressions and mental phenomena
that are continuously changing. The teachings list six triggers that can result in the generation of different mental events. These triggers are input from the five senses (seeing, hearing,
smelling, tasting or touch sensations), or a thought (relating to the
past, present or the future) that happen to arise in the mind. The
mental events generated as a result of these triggers are: feelings,
perceptions and intentions/behavior. The moment-by-moment manifestation
of the mind-stream is said to happen in every person all the time. It
even happens in a scientist who analyzes various phenomena in the world,
or analyzes the material body including the organ brain. The manifestation of the mindstream is also described as being
influenced by physical laws, biological laws, psychological laws,
volitional laws, and universal laws. The purpose of the Buddhist practice of mindfulness is to understand the inherent nature of the consciousness and its characteristics.
Narrative form
In the West, the primary impact of the idea has been on literature rather than science: "stream of consciousness as a narrative mode"
means writing in a way that attempts to portray the moment-to-moment
thoughts and experiences of a character. This technique perhaps had its
beginnings in the monologues of Shakespeare's plays and reached its
fullest development in the novels of James Joyce and Virginia Woolf, although it has also been used by many other noted writers.
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 well-educated woman certainly and her gabby talk about Mr Riordan
here and Mr Riordan there I suppose he was glad to get shut of her.
The Upanishads hold the oldest recorded map of consciousness, as explored by sages through meditation.
The Canadian psychiatrist Richard Maurice Bucke, author of the 1901 book Cosmic Consciousness: A Study in the Evolution of the Human Mind,
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 have attained "intellectual enlightenment
or illumination".
Another thorough account of the spiritual approach is Ken Wilber's 1977 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.
