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Facing Up to the Problem of Consciousness
The vague term "consciousness" poses the most baffling problems in the science of the mind. Philosopher David Chalmers presents a nonreductive theory of consciousness based on principles of structural coherence (tied to awareness) and organizational invariance (e.g., a silicon isomorph of a human can be conscious) and a double-aspect view of information (physical and phenomenal aspects).
Published on KurzweilAI.net August 17, 2002
[This appeared in the Journal of Consciousness Studies
in 1995. Also online is my response, "Moving
Forward on the problem of Consciousness," to 26 articles
commenting on this paper. That paper elaborates and extends many
of the ideas in this one. -- David Chalmers]
1 Introduction
Consciousness poses the most baffling problems in the science of
the mind. There is nothing that we know more intimately than conscious
experience, but there is nothing that is harder to explain. All
sorts of mental phenomena have yielded to scientific investigation
in recent years, but consciousness has stubbornly resisted. Many
have tried to explain it, but the explanations always seem to fall
short of the target. Some have been led to suppose that the problem
is intractable, and that no good explanation can be given.
To make progress on the problem of consciousness, we have to confront
it directly. In this paper, I first isolate the truly hard part
of the problem, separating it from more tractable parts and giving
an account of why it is so difficult to explain. I critique some
recent work that uses reductive methods to address consciousness,
and argue that such methods inevitably fail to come to grips with
the hardest part of the problem. Once this failure is recognized,
the door to further progress is opened. In the second half of the
paper, I argue that if we move to a new kind of nonreductive explanation,
a naturalistic account of consciousness can be given. I put forward
my own candidate for such an account: a nonreductive theory based
on principles of structural coherence and organizational invariance
and a double-aspect view of information.
2 The easy problems and the hard problem
There is not just one problem of consciousness. "Consciousness"
is an ambiguous term, referring to many different phenomena. Each
of these phenomena needs to be explained, but some are easier to
explain than others. At the start, it is useful to divide the associated
problems of consciousness into "hard" and "easy"
problems. The easy problems of consciousness are those that seem
directly susceptible to the standard methods of cognitive science,
whereby a phenomenon is explained in terms of computational or neural
mechanisms. The hard problems are those that seem to resist those
methods.
The easy problems of consciousness include those of explaining
the following phenomena:
- the ability to discriminate, categorize, and react to environmental
stimuli;
- the integration of information by a cognitive system;
- the reportability of mental states;
- the ability of a system to access its own internal states;
- the focus of attention;
- the deliberate control of behavior;
- the difference between wakefulness and sleep.
All of these phenomena are associated with the notion of consciousness.
For example, one sometimes says that a mental state is conscious
when it is verbally reportable, or when it is internally accessible.
Sometimes a system is said to be conscious of some information when
it has the ability to react on the basis of that information, or,
more strongly, when it attends to that information, or when it can
integrate that information and exploit it in the sophisticated control
of behavior. We sometimes say that an action is conscious precisely
when it is deliberate. Often, we say that an organism is conscious
as another way of saying that it is awake.
There is no real issue about whether these phenomena can
be explained scientifically. All of them are straightforwardly vulnerable
to explanation in terms of computational or neural mechanisms. To
explain access and reportability, for example, we need only specify
the mechanism by which information about internal states is retrieved
and made available for verbal report. To explain the integration
of information, we need only exhibit mechanisms by which information
is brought together and exploited by later processes. For an account
of sleep and wakefulness, an appropriate neurophysiological account
of the processes responsible for organisms' contrasting behavior
in those states will suffice. In each case, an appropriate cognitive
or neurophysiological model can clearly do the explanatory work.
If these phenomena were all there was to consciousness, then consciousness
would not be much of a problem. Although we do not yet have anything
close to a complete explanation of these phenomena, we have a clear
idea of how we might go about explaining them. This is why I call
these problems the easy problems. Of course, "easy" is
a relative term. Getting the details right will probably take a
century or two of difficult empirical work. Still, there is every
reason to believe that the methods of cognitive science and neuroscience
will succeed.
The really hard problem of consciousness is the problem of experience.
When we think and perceive, there is a whir of information-processing,
but there is also a subjective aspect. As Nagel (1974) has put it,
there is something it is like to be a conscious organism.
This subjective aspect is experience. When we see, for example,
we experience visual sensations: the felt quality of redness,
the experience of dark and light, the quality of depth in a visual
field. Other experiences go along with perception in different modalities:
the sound of a clarinet, the smell of mothballs. Then there are
bodily sensations, from pains to orgasms; mental images that are
conjured up internally; the felt quality of emotion, and the experience
of a stream of conscious thought. What unites all of these states
is that there is something it is like to be in them. All of them
are states of experience.
It is undeniable that some organisms are subjects of experience.
But the question of how it is that these systems are subjects of
experience is perplexing. Why is it that when our cognitive systems
engage in visual and auditory information-processing, we have visual
or auditory experience: the quality of deep blue, the sensation
of middle C? How can we explain why there is something it is like
to entertain a mental image, or to experience an emotion? It is
widely agreed that experience arises from a physical basis, but
we have no good explanation of why and how it so arises. Why should
physical processing give rise to a rich inner life at all? It seems
objectively unreasonable that it should, and yet it does.
If any problem qualifies as the problem of consciousness,
it is this one. In this central sense of "consciousness,"
an organism is conscious if there is something it is like to be
that organism, and a mental state is conscious if there is something
it is like to be in that state. Sometimes terms such as "phenomenal
consciousness" and "qualia" are also used here, but
I find it more natural to speak of "conscious experience"
or simply "experience." Another useful way to avoid confusion
(used by e.g. Newell 1990, Chalmers 1996) is to reserve the term
"consciousness" for the phenomena of experience, using
the less loaded term "awareness" for the more straightforward
phenomena described earlier. If such a convention were widely adopted,
communication would be much easier; as things stand, those who talk
about "consciousness" are frequently talking past each
other.
The ambiguity of the term "consciousness" is often exploited
by both philosophers and scientists writing on the subject. It is
common to see a paper on consciousness begin with an invocation
of the mystery of consciousness, noting the strange intangibility
and ineffability of subjectivity, and worrying that so far we have
no theory of the phenomenon. Here, the topic is clearly the hard
problem - the problem of experience. In the second half of the paper,
the tone becomes more optimistic, and the author's own theory of
consciousness is outlined. Upon examination, this theory turns out
to be a theory of one of the more straightforward phenomena - of
reportability, of introspective access, or whatever. At the close,
the author declares that consciousness has turned out to be tractable
after all, but the reader is left feeling like the victim of a bait-and-switch.
The hard problem remains untouched.
3 Functional explanation
Why are the easy problems easy, and why is the hard problem hard?
The easy problems are easy precisely because they concern the explanation
of cognitive abilities and functions. To explain a
cognitive function, we need only specify a mechanism that can perform
the function. The methods of cognitive science are well-suited for
this sort of explanation, and so are well-suited to the easy problems
of consciousness. By contrast, the hard problem is hard precisely
because it is not a problem about the performance of functions.
The problem persists even when the performance of all the relevant
functions is explained. (Here "function" is not used in
the narrow teleological sense of something that a system is designed
to do, but in the broader sense of any causal role in the production
of behavior that a system might perform.)
To explain reportability, for instance, is just to explain how
a system could perform the function of producing reports on internal
states. To explain internal access, we need to explain how a system
could be appropriately affected by its internal states and use information
about those states in directing later processes. To explain integration
and control, we need to explain how a system's central processes
can bring information contents together and use them in the facilitation
of various behaviors. These are all problems about the explanation
of functions.
How do we explain the performance of a function? By specifying
a mechanism that performs the function. Here, neurophysiological
and cognitive modeling are perfect for the task. If we want a detailed
low-level explanation, we can specify the neural mechanism that
is responsible for the function. If we want a more abstract explanation,
we can specify a mechanism in computational terms. Either way, a
full and satisfying explanation will result. Once we have specified
the neural or computational mechanism that performs the function
of verbal report, for example, the bulk of our work in explaining
reportability is over.
In a way, the point is trivial. It is a conceptual fact
about these phenomena that their explanation only involves the explanation
of various functions, as the phenomena are functionally definable.
All it means for reportability to be instantiated in a system
is that the system has the capacity for verbal reports of internal
information. All it means for a system to be awake is for it to
be appropriately receptive to information from the environment and
for it to be able to use this information in directing behavior
in an appropriate way. To see that this sort of thing is a conceptual
fact, note that someone who says "you have explained the performance
of the verbal report function, but you have not explained reportability"
is making a trivial conceptual mistake about reportability. All
it could possibly take to explain reportability is an explanation
of how the relevant function is performed; the same goes for the
other phenomena in question.
Throughout the higher-level sciences, reductive explanation works
in just this way. To explain the gene, for instance, we needed to
specify the mechanism that stores and transmits hereditary information
from one generation to the next. It turns out that DNA performs
this function; once we explain how the function is performed, we
have explained the gene. To explain life, we ultimately need to
explain how a system can reproduce, adapt to its environment, metabolize,
and so on. All of these are questions about the performance of functions,
and so are well-suited to reductive explanation. The same holds
for most problems in cognitive science. To explain learning, we
need to explain the way in which a system's behavioral capacities
are modified in light of environmental information, and the way
in which new information can be brought to bear in adapting a system's
actions to its environment. If we show how a neural or computational
mechanism does the job, we have explained learning. We can say the
same for other cognitive phenomena, such as perception, memory,
and language. Sometimes the relevant functions need to be characterized
quite subtly, but it is clear that insofar as cognitive science
explains these phenomena at all, it does so by explaining the performance
of functions.
When it comes to conscious experience, this sort of explanation
fails. What makes the hard problem hard and almost unique is that
it goes beyond problems about the performance of functions.
To see this, note that even when we have explained the performance
of all the cognitive and behavioral functions in the vicinity of
experience - perceptual discrimination, categorization, internal
access, verbal report - there may still remain a further unanswered
question: Why is the performance of these functions accompanied
by experience? A simple explanation of the functions leaves
this question open.
There is no analogous further question in the explanation of genes,
or of life, or of learning. If someone says "I can see that
you have explained how DNA stores and transmits hereditary information
from one generation to the next, but you have not explained how
it is a gene," then they are making a conceptual mistake.
All it means to be a gene is to be an entity that performs the relevant
storage and transmission function. But if someone says "I can
see that you have explained how information is discriminated, integrated,
and reported, but you have not explained how it is experienced,"
they are not making a conceptual mistake. This is a nontrivial further
question.
This further question is the key question in the problem of consciousness.
Why doesn't all this information-processing go on "in the dark,"
free of any inner feel? Why is it that when electromagnetic waveforms
impinge on a retina and are discriminated and categorized by a visual
system, this discrimination and categorization is experienced as
a sensation of vivid red? We know that conscious experience does
arise when these functions are performed, but the very fact that
it arises is the central mystery. There is an explanatory gap
(a term due to Levine 1983) between the functions and experience,
and we need an explanatory bridge to cross it. A mere account of
the functions stays on one side of the gap, so the materials for
the bridge must be found elsewhere.
This is not to say that experience has no function. Perhaps
it will turn out to play an important cognitive role. But for any
role it might play, there will be more to the explanation of experience
than a simple explanation of the function. Perhaps it will even
turn out that in the course of explaining a function, we will be
led to the key insight that allows an explanation of experience.
If this happens, though, the discovery will be an extra explanatory
reward. There is no cognitive function such that we can say in advance
that explanation of that function will automatically explain
experience.
To explain experience, we need a new approach. The usual explanatory
methods of cognitive science and neuroscience do not suffice. These
methods have been developed precisely to explain the performance
of cognitive functions, and they do a good job of it. But as these
methods stand, they are only equipped to explain the performance
of functions. When it comes to the hard problem, the standard approach
has nothing to say.
4 Some case-studies
In the last few years, a number of works have addressed the problems
of consciousness within the framework of cognitive science and neuroscience.
This might suggest that the analysis above is faulty, but in fact
a close examination of the relevant work only lends the analysis
further support. When we investigate just which aspects of consciousness
these studies are aimed at, and which aspects they end up explaining,
we find that the ultimate target of explanation is always one of
the easy problems. I will illustrate this with two representative
examples.
The first is the "neurobiological theory of consciousness"
outlined by Crick and Koch (1990; see also Crick 1994). This theory
centers on certain 35-75 hertz neural oscillations in the cerebral
cortex; Crick and Koch hypothesize that these oscillations are the
basis of consciousness. This is partly because the oscillations
seem to be correlated with awareness in a number of different modalities
- within the visual and olfactory systems, for example - and also
because they suggest a mechanism by which the binding of
information contents might be achieved. Binding is the process whereby
separately represented pieces of information about a single entity
are brought together to be used by later processing, as when information
about the color and shape of a perceived object is integrated from
separate visual pathways. Following others (e.g., Eckhorn et
al 1988), Crick and Koch hypothesize that binding may be achieved
by the synchronized oscillations of neuronal groups representing
the relevant contents. When two pieces of information are to be
bound together, the relevant neural groups will oscillate with the
same frequency and phase.
The details of how this binding might be achieved are still poorly
understood, but suppose that they can be worked out. What might
the resulting theory explain? Clearly it might explain the binding
of information contents, and perhaps it might yield a more general
account of the integration of information in the brain. Crick and
Koch also suggest that these oscillations activate the mechanisms
of working memory, so that there may be an account of this and perhaps
other forms of memory in the distance. The theory might eventually
lead to a general account of how perceived information is bound
and stored in memory, for use by later processing.
Such a theory would be valuable, but it would tell us nothing about
why the relevant contents are experienced. Crick and Koch suggest
that these oscillations are the neural correlates of experience.
This claim is arguable - does not binding also take place in the
processing of unconscious information? - but even if it is accepted,
the explanatory question remains: Why do the oscillations
give rise to experience? The only basis for an explanatory connection
is the role they play in binding and storage, but the question of
why binding and storage should themselves be accompanied by experience
is never addressed. If we do not know why binding and storage should
give rise to experience, telling a story about the oscillations
cannot help us. Conversely, if we knew why binding and storage
gave rise to experience, the neurophysiological details would be
just the icing on the cake. Crick and Koch's theory gains its purchase
by assuming a connection between binding and experience,
and so can do nothing to explain that link.
I do not think that Crick and Koch are ultimately claiming to address
the hard problem, although some have interpreted them otherwise.
A published interview with Koch gives a clear statement of the limitations
on the theory's ambitions.
Well, let's first forget about the really difficult aspects,
like subjective feelings, for they may not have a scientific solution.
The subjective state of play, of pain, of pleasure, of seeing
blue, of smelling a rose - there seems to be a huge jump between
the materialistic level, of explaining molecules and neurons,
and the subjective level. Let's focus on things that are easier
to study - like visual awareness. You're now talking to me, but
you're not looking at me, you're looking at the cappuccino, and
so you are aware of it. You can say, `It's a cup and there's some
liquid in it.' If I give it to you, you'll move your arm and you'll
take it - you'll respond in a meaningful manner. That's what I
call awareness." ("What is Consciousness," Discover,
November 1992, p. 96.)
The second example is an approach at the level of cognitive psychology.
This is Baars' global workspace theory of consciousness, presented
in his book A Cognitive Theory of Consciousness. According
to this theory, the contents of consciousness are contained in a
global workspace, a central processor used to mediate communication
between a host of specialized nonconscious processors. When these
specialized processors need to broadcast information to the rest
of the system, they do so by sending this information to the workspace,
which acts as a kind of communal blackboard for the rest of the
system, accessible to all the other processors.
Baars uses this model to address many aspects of human cognition,
and to explain a number of contrasts between conscious and unconscious
cognitive functioning. Ultimately, however, it is a theory of cognitive
accessibility, explaining how it is that certain information
contents are widely accessible within a system, as well as a theory
of informational integration and reportability. The theory shows
promise as a theory of awareness, the functional correlate of conscious
experience, but an explanation of experience itself is not on offer.
One might suppose that according to this theory, the contents of
experience are precisely the contents of the workspace. But even
if this is so, nothing internal to the theory explains why
the information within the global workspace is experienced. The
best the theory can do is to say that the information is experienced
because it is globally accessible. But now the question arises
in a different form: why should global accessibility give rise to
conscious experience? As always, this bridging question is unanswered.
Almost all work taking a cognitive or neuroscientific approach
to consciousness in recent years could be subjected to a similar
critique. The "Neural Darwinism" model of Edelman (1989),
for instance, addresses questions about perceptual awareness and
the self-concept, but says nothing about why there should also be
experience. The "multiple drafts" model of Dennett (1991)
is largely directed at explaining the reportability of certain mental
contents. The "intermediate level" theory of Jackendoff
(1988) provides an account of some computational processes that
underlie consciousness, but Jackendoff stresses that the question
of how these "project" into conscious experience remains
mysterious.
Researchers using these methods are often inexplicit about their
attitudes to the problem of conscious experience, although sometimes
they take a clear stand. Even among those who are clear about it,
attitudes differ widely. In placing this sort of work with respect
to the problem of experience, a number of different strategies are
available. It would be useful if these strategic choices were more
often made explicit.
The first strategy is simply to explain something else.
Some researchers are explicit that the problem of experience is
too difficult for now, and perhaps even outside the domain of science
altogether. These researchers instead choose to address one of the
more tractable problems such as reportability or the self-concept.
Although I have called these problems the "easy" problems,
they are among the most interesting unsolved problems in cognitive
science, so this work is certainly worthwhile. The worst that can
be said of this choice is that in the context of research on consciousness
it is relatively unambitious, and the work can sometimes be misinterpreted.
The second choice is to take a harder line and deny the phenomenon.
(Variations on this approach are taken by Allport 1988, Dennett
1991, and Wilkes 1988.) According to this line, once we have explained
the functions such as accessibility, reportability, and the like,
there is no further phenomenon called "experience" to
explain. Some explicitly deny the phenomenon, holding for example
that what is not externally verifiable cannot be real. Others achieve
the same effect by allowing that experience exists, but only if
we equate "experience" with something like the capacity
to discriminate and report. These approaches lead to a simpler theory,
but are ultimately unsatisfactory. Experience is the most central
and manifest aspect of our mental lives, and indeed is perhaps the
key explanandum in the science of the mind. Because of this status
as an explanandum, experience cannot be discarded like the vital
spirit when a new theory comes along. Rather, it is the central
fact that any theory of consciousness must explain. A theory that
denies the phenomenon "solves" the problem by ducking
the question.
In a third option, some researchers claim to be explaining experience
in the full sense. These researchers (unlike those above) wish to
take experience very seriously; they lay out their functional model
or theory, and claim that it explains the full subjective quality
of experience (e.g. Flohr 1992, Humphrey 1992). The relevant step
in the explanation is usually passed over quickly, however, and
usually ends up looking something like magic. After some details
about information processing are given, experience suddenly enters
the picture, but it is left obscure how these processes should
suddenly give rise to experience. Perhaps it is simply taken for
granted that it does, but then we have an incomplete explanation
and a version of the fifth strategy below.
A fourth, more promising approach appeals to these methods to explain
the structure of experience. For example, it is arguable that
an account of the discriminations made by the visual system can
account for the structural relations between different color experiences,
as well as for the geometric structure of the visual field (see
e.g., Clark 1992 and Hardin 1992). In general, certain facts about
structures found in processing will correspond to and arguably explain
facts about the structure of experience. This strategy is plausible
but limited. At best, it takes the existence of experience for granted
and accounts for some facts about its structure, providing a sort
of nonreductive explanation of the structural aspects of experience
(I will say more on this later). This is useful for many purposes,
but it tells us nothing about why there should be experience in
the first place.
A fifth and reasonable strategy is to isolate the substrate
of experience. After all, almost everyone allows that experience
arises one way or another from brain processes, and it makes
sense to identify the sort of process from which it arises. Crick
and Koch put their work forward as isolating the neural correlate
of consciousness, for example, and Edelman (1989) and Jackendoff
(1988) make related claims. Justification of these claims requires
a careful theoretical analysis, especially as experience is not
directly observable in experimental contexts, but when applied judiciously
this strategy can shed indirect light on the problem of experience.
Nevertheless, the strategy is clearly incomplete. For a satisfactory
theory, we need to know more than which processes give rise
to experience; we need an account of why and how. A full theory
of consciousness must build an explanatory bridge.
5 The extra ingredient
We have seen that there are systematic reasons why the usual methods
of cognitive science and neuroscience fail to account for conscious
experience. These are simply the wrong sort of methods: nothing
that they give to us can yield an explanation. To account for conscious
experience, we need an extra ingredient in the explanation.
This makes for a challenge to those who are serious about the hard
problem of consciousness: What is your extra ingredient, and why
should that account for conscious experience?
There is no shortage of extra ingredients to be had. Some propose
an injection of chaos and nonlinear dynamics. Some think that the
key lies in nonalgorithmic processing. Some appeal to future discoveries
in neurophysiology. Some suppose that the key to the mystery will
lie at the level of quantum mechanics. It is easy to see why all
these suggestions are put forward. None of the old methods work,
so the solution must lie with something new. Unfortunately,
these suggestions all suffer from the same old problems.
Nonalgorithmic processing, for example, is put forward by Penrose
(1989; 1994) because of the role it might play in the process of
conscious mathematical insight. The arguments about mathematics
are controversial, but even if they succeed and an account of nonalgorithmic
processing in the human brain is given, it will still only be an
account of the functions involved in mathematical reasoning
and the like. For a nonalgorithmic process as much as an algorithmic
process, the question is left unanswered: why should this process
give rise to experience? In answering this question, there
is no special role for nonalgorithmic processing.
The same goes for nonlinear and chaotic dynamics. These might provide
a novel account of the dynamics of cognitive functioning, quite
different from that given by standard methods in cognitive science.
But from dynamics, one only gets more dynamics. The question about
experience here is as mysterious as ever. The point is even clearer
for new discoveries in neurophysiology. These new discoveries may
help us make significant progress in understanding brain function,
but for any neural process we isolate, the same question will always
arise. It is difficult to imagine what a proponent of new neurophysiology
expects to happen, over and above the explanation of further cognitive
functions. It is not as if we will suddenly discover a phenomenal
glow inside a neuron!
Perhaps the most popular "extra ingredient" of all is
quantum mechanics (e.g. Hameroff 1994). The attractiveness of quantum
theories of consciousness may stem from a Law of Minimization of
Mystery: consciousness is mysterious and quantum mechanics is mysterious,
so maybe the two mysteries have a common source. Nevertheless, quantum
theories of consciousness suffer from the same difficulties as neural
or computational theories. Quantum phenomena have some remarkable
functional properties, such as nondeterminism and nonlocality. It
is natural to speculate that these properties may play some role
in the explanation of cognitive functions, such as random choice
and the integration of information, and this hypothesis cannot be
ruled out a priori. But when it comes to the explanation
of experience, quantum processes are in the same boat as any other.
The question of why these processes should give rise to experience
is entirely unanswered.
(One special attraction of quantum theories is the fact that on
some interpretations of quantum mechanics, consciousness plays an
active role in "collapsing" the quantum wave function.
Such interpretations are controversial, but in any case they offer
no hope of explaining consciousness in terms of quantum processes.
Rather, these theories assume the existence of consciousness,
and use it in the explanation of quantum processes. At best, these
theories tell us something about a physical role that consciousness
may play. They tell us nothing about how it arises.)
At the end of the day, the same criticism applies to any
purely physical account of consciousness. For any physical process
we specify there will be an unanswered question: Why should this
process give rise to experience? Given any such process, it is conceptually
coherent that it could be instantiated in the absence of experience.
It follows that no mere account of the physical process will tell
us why experience arises. The emergence of experience goes beyond
what can be derived from physical theory.
Purely physical explanation is well-suited to the explanation of
physical structures, explaining macroscopic structures in
terms of detailed microstructural constituents; and it provides
a satisfying explanation of the performance of functions,
accounting for these functions in terms of the physical mechanisms
that perform them. This is because a physical account can entail
the facts about structures and functions: once the internal details
of the physical account are given, the structural and functional
properties fall out as an automatic consequence. But the structure
and dynamics of physical processes yield only more structure and
dynamics, so structures and functions are all we can expect these
processes to explain. The facts about experience cannot be an automatic
consequence of any physical account, as it is conceptually coherent
that any given process could exist without experience. Experience
may arise from the physical, but it is not entailed
by the physical.
The moral of all this is that you can't explain conscious experience
on the cheap. It is a remarkable fact that reductive methods
- methods that explain a high-level phenomenon wholly in terms of
more basic physical processes - work well in so many domains. In
a sense, one can explain most biological and cognitive phenomena
on the cheap, in that these phenomena are seen as automatic consequences
of more fundamental processes. It would be wonderful if reductive
methods could explain experience, too; I hoped for a long time that
they might. Unfortunately, there are systematic reasons why these
methods must fail. Reductive methods are successful in most domains
because what needs explaining in those domains are structures and
functions, and these are the kind of thing that a physical account
can entail. When it comes to a problem over and above the explanation
of structures and functions, these methods are impotent.
This might seem reminiscent of the vitalist claim that no physical
account could explain life, but the cases are disanalogous. What
drove vitalist skepticism was doubt about whether physical mechanisms
could perform the many remarkable functions associated with life,
such as complex adaptive behavior and reproduction. The conceptual
claim that explanation of functions is what is needed was implicitly
accepted, but lacking detailed knowledge of biochemical mechanisms,
vitalists doubted whether any physical process could do the job
and put forward the hypothesis of the vital spirit as an alternative
explanation. Once it turned out that physical processes could perform
the relevant functions, vitalist doubts melted away.
With experience, on the other hand, physical explanation of the
functions is not in question. The key is instead the conceptual
point that the explanation of functions does not suffice for the
explanation of experience. This basic conceptual point is not something
that further neuroscientific investigation will affect. In a similar
way, experience is disanalogous to the élan vital.
The vital spirit was put forward as an explanatory posit, in order
to explain the relevant functions, and could therefore be discarded
when those functions were explained without it. Experience is not
an explanatory posit but an explanandum in its own right, and so
is not a candidate for this sort of elimination.
It is tempting to note that all sorts of puzzling phenomena have
eventually turned out to be explainable in physical terms. But each
of these were problems about the observable behavior of physical
objects, coming down to problems in the explanation of structures
and functions. Because of this, these phenomena have always been
the kind of thing that a physical account might explain,
even if at some points there have been good reasons to suspect that
no such explanation would be forthcoming. The tempting induction
from these cases fails in the case of consciousness, which is not
a problem about physical structures and functions. The problem of
consciousness is puzzling in an entirely different way. An analysis
of the problem shows us that conscious experience is just not the
kind of thing that a wholly reductive account could succeed in explaining.
6 Nonreductive explanation
At this point some are tempted to give up, holding that we will
never have a theory of conscious experience. McGinn (1989), for
example, argues that the problem is too hard for our limited minds;
we are "cognitively closed" with respect to the phenomenon.
Others have argued that conscious experience lies outside the domain
of scientific theory altogether.
I think this pessimism is premature. This is not the place to give
up; it is the place where things get interesting. When simple methods
of explanation are ruled out, we need to investigate the alternatives.
Given that reductive explanation fails, nonreductive explanation
is the natural choice.
Although a remarkable number of phenomena have turned out to be
explicable wholly in terms of entities simpler than themselves,
this is not universal. In physics, it occasionally happens that
an entity has to be taken as fundamental. Fundamental entities
are not explained in terms of anything simpler. Instead, one takes
them as basic, and gives a theory of how they relate to everything
else in the world. For example, in the nineteenth century it turned
out that electromagnetic processes could not be explained in terms
of the wholly mechanical processes that previous physical theories
appealed to, so Maxwell and others introduced electromagnetic charge
and electromagnetic forces as new fundamental components of a physical
theory. To explain electromagnetism, the ontology of physics had
to be expanded. New basic properties and basic laws were needed
to give a satisfactory account of the phenomena.
Other features that physical theory takes as fundamental include
mass and space-time. No attempt is made to explain these features
in terms of anything simpler. But this does not rule out the possibility
of a theory of mass or of space-time. There is an intricate theory
of how these features interrelate, and of the basic laws they enter
into. These basic principles are used to explain many familiar phenomena
concerning mass, space, and time at a higher level.
I suggest that a theory of consciousness should take experience
as fundamental. We know that a theory of consciousness requires
the addition of something fundamental to our ontology, as
everything in physical theory is compatible with the absence of
consciousness. We might add some entirely new nonphysical feature,
from which experience can be derived, but it is hard to see what
such a feature would be like. More likely, we will take experience
itself as a fundamental feature of the world, alongside mass, charge,
and space-time. If we take experience as fundamental, then we can
go about the business of constructing a theory of experience.
Where there is a fundamental property, there are fundamental laws.
A nonreductive theory of experience will add new principles to the
furniture of the basic laws of nature. These basic principles will
ultimately carry the explanatory burden in a theory of consciousness.
Just as we explain familiar high-level phenomena involving mass
in terms of more basic principles involving mass and other entities,
we might explain familiar phenomena involving experience in terms
of more basic principles involving experience and other entities.
In particular, a nonreductive theory of experience will specify
basic principles telling us how experience depends on physical features
of the world. These psychophysical principles will not interfere
with physical laws, as it seems that physical laws already form
a closed system. Rather, they will be a supplement to a physical
theory. A physical theory gives a theory of physical processes,
and a psychophysical theory tells us how those processes give rise
to experience. We know that experience depends on physical processes,
but we also know that this dependence cannot be derived from physical
laws alone. The new basic principles postulated by a nonreductive
theory give us the extra ingredient that we need to build an explanatory
bridge.
Of course, by taking experience as fundamental, there is a sense
in which this approach does not tell us why there is experience
in the first place. But this is the same for any fundamental theory.
Nothing in physics tells us why there is matter in the first place,
but we do not count this against theories of matter. Certain features
of the world need to be taken as fundamental by any scientific theory.
A theory of matter can still explain all sorts of facts about matter,
by showing how they are consequences of the basic laws. The same
goes for a theory of experience.
This position qualifies as a variety of dualism, as it postulates
basic properties over and above the properties invoked by physics.
But it is an innocent version of dualism, entirely compatible with
the scientific view of the world. Nothing in this approach contradicts
anything in physical theory; we simply need to add further bridging
principles to explain how experience arises from physical processes.
There is nothing particularly spiritual or mystical about this theory
- its overall shape is like that of a physical theory, with a few
fundamental entities connected by fundamental laws. It expands the
ontology slightly, to be sure, but Maxwell did the same thing. Indeed,
the overall structure of this position is entirely naturalistic,
allowing that ultimately the universe comes down to a network of
basic entities obeying simple laws, and allowing that there may
ultimately be a theory of consciousness cast in terms of such laws.
If the position is to have a name, a good choice might be naturalistic
dualism.
If this view is right, then in some ways a theory of consciousness
will have more in common with a theory in physics than a theory
in biology. Biological theories involve no principles that are fundamental
in this way, so biological theory has a certain complexity and messiness
to it; but theories in physics, insofar as they deal with fundamental
principles, aspire to simplicity and elegance. The fundamental laws
of nature are part of the basic furniture of the world, and physical
theories are telling us that this basic furniture is remarkably
simple. If a theory of consciousness also involves fundamental principles,
then we should expect the same. The principles of simplicity, elegance,
and even beauty that drive physicists' search for a fundamental
theory will also apply to a theory of consciousness.
(A technical note: Some philosophers argue that even though there
is a conceptual gap between physical processes and experience,
there need be no metaphysical gap, so that experience might in a
certain sense still be physical (e.g. Hill 1991; Levine 1983; Loar
1990). Usually this line of argument is supported by an appeal to
the notion of a posteriori necessity (Kripke 1980). I think
that this position rests on a misunderstanding of a posteriori
necessity, however, or else requires an entirely new sort of necessity
that we have no reason to believe in; see Chalmers 1996 (also Jackson
1994 and Lewis 1994) for details. In any case, this position still
concedes an explanatory gap between physical processes and
experience. For example, the principles connecting the physical
and the experiential will not be derivable from the laws of physics,
so such principles must be taken as explanatorily fundamental.
So even on this sort of view, the explanatory structure of a theory
of consciousness will be much as I have described.)
It is not too soon to begin work on a theory. We are already in
a position to understand certain key facts about the relationship
between physical processes and experience, and about the regularities
that connect them. Once reductive explanation is set aside, we can
lay those facts on the table so that they can play their proper
role as the initial pieces in a nonreductive theory of consciousness,
and as constraints on the basic laws that constitute an ultimate
theory.
There is an obvious problem that plagues the development of a theory
of consciousness, and that is the paucity of objective data. Conscious
experience is not directly observable in an experimental context,
so we cannot generate data about the relationship between physical
processes and experience at will. Nevertheless, we all have access
to a rich source of data in our own case. Many important regularities
between experience and processing can be inferred from considerations
about one's own experience. There are also good indirect sources
of data from observable cases, as when one relies on the verbal
report of a subject as an indication of experience. These methods
have their limitations, but we have more than enough data to get
a theory off the ground.
Philosophical analysis is also useful in getting value for money
out of the data we have. This sort of analysis can yield a number
of principles relating consciousness and cognition, thereby strongly
constraining the shape of an ultimate theory. The method of thought-experimentation
can also yield significant rewards, as we will see. Finally, the
fact that we are searching for a fundamental theory means
that we can appeal to such nonempirical constraints as simplicity,
homogeneity, and the like in developing a theory. We must seek to
systematize the information we have, to extend it as far as possible
by careful analysis, and then make the inference to the simplest
possible theory that explains the data while remaining a plausible
candidate to be part of the fundamental furniture of the world.
Such theories will always retain an element of speculation that
is not present in other scientific theories, because of the impossibility
of conclusive intersubjective experimental tests. Still, we can
certainly construct theories that are compatible with the data that
we have, and evaluate them in comparison to each other. Even in
the absence of intersubjective observation, there are numerous criteria
available for the evaluation of such theories: simplicity, internal
coherence, coherence with theories in other domains, the ability
to reproduce the properties of experience that are familiar from
our own case, and even an overall fit with the dictates of common
sense. Perhaps there will be significant indeterminacies remaining
even when all these constraints are applied, but we can at least
develop plausible candidates. Only when candidate theories have
been developed will we be able to evaluate them.
A nonreductive theory of consciousness will consist in a number
of psychophysical principles, principles connecting the properties
of physical processes to the properties of experience. We can think
of these principles as encapsulating the way in which experience
arises from the physical. Ultimately, these principles should tell
us what sort of physical systems will have associated experiences,
and for the systems that do, they should tell us what sort of physical
properties are relevant to the emergence of experience, and just
what sort of experience we should expect any given physical system
to yield. This is a tall order, but there is no reason why we should
not get started.
In what follows, I present my own candidates for the psychophysical
principles that might go into a theory of consciousness. The first
two of these are nonbasic principles - systematic connections
between processing and experience at a relatively high level. These
principles can play a significant role in developing and constraining
a theory of consciousness, but they are not cast at a sufficiently
fundamental level to qualify as truly basic laws. The final principle
is my candidate for a basic principle that might form the
cornerstone of a fundamental theory of consciousness. This final
principle is particularly speculative, but it is the kind of speculation
that is required if we are ever to have a satisfying theory of consciousness.
I can present these principles only briefly here; I argue for them
at much greater length in Chalmers (1996).
1. The principle of structural coherence. This is a principle
of coherence between the structure of consciousness and the
structure of awareness. Recall that "awareness"
was used earlier to refer to the various functional phenomena that
are associated with consciousness. I am now using it to refer to
a somewhat more specific process in the cognitive underpinnings
of experience. In particular, the contents of awareness are to be
understood as those information contents that are accessible to
central systems, and brought to bear in a widespread way in the
control of behavior. Briefly put, we can think of awareness as direct
availability for global control. To a first approximation, the
contents of awareness are the contents that are directly accessible
and potentially reportable, at least in a language-using system.
Awareness is a purely functional notion, but it is nevertheless
intimately linked to conscious experience. In familiar cases, wherever
we find consciousness, we find awareness. Wherever there is conscious
experience, there is some corresponding information in the cognitive
system that is available in the control of behavior, and available
for verbal report. Conversely, it seems that whenever information
is available for report and for global control, there is a corresponding
conscious experience. Thus, there is a direct correspondence between
consciousness and awareness.
The correspondence can be taken further. It is a central fact about
experience that it has a complex structure. The visual field has
a complex geometry, for instance. There are also relations of similarity
and difference between experiences, and relations in such things
as relative intensity. Every subject's experience can be at least
partly characterized and decomposed in terms of these structural
properties: similarity and difference relations, perceived location,
relative intensity, geometric structure, and so on. It is also a
central fact that to each of these structural features, there is
a corresponding feature in the information-processing structure
of awareness.
Take color sensations as an example. For every distinction between
color experiences, there is a corresponding distinction in processing.
The different phenomenal colors that we experience form a complex
three-dimensional space, varying in hue, saturation, and intensity.
The properties of this space can be recovered from information-processing
considerations: examination of the visual systems shows that waveforms
of light are discriminated and analyzed along three different axes,
and it is this three-dimensional information that is relevant to
later processing. The three-dimensional structure of phenomenal
color space therefore corresponds directly to the three dimensional
structure of visual awareness. This is precisely what we would expect.
After all, every color distinction corresponds to some reportable
information, and therefore to a distinction that is represented
in the structure of processing.
In a more straightforward way, the geometric structure of the visual
field is directly reflected in a structure that can be recovered
from visual processing. Every geometric relation corresponds to
something that can be reported and is therefore cognitively represented.
If we were given only the story about information-processing in
an agent's visual and cognitive system, we could not directly
observe that agent's visual experiences, but we could nevertheless
infer those experiences' structural properties.
In general, any information that is consciously experienced will
also be cognitively represented. The fine-grained structure of the
visual field will correspond to some fine-grained structure in visual
processing. The same goes for experiences in other modalities, and
even for nonsensory experiences. Internal mental images have geometric
properties that are represented in processing. Even emotions have
structural properties, such as relative intensity, that correspond
directly to a structural property of processing; where there is
greater intensity, we find a greater effect on later processes.
In general, precisely because the structural properties of experience
are accessible and reportable, those properties will be directly
represented in the structure of awareness.
It is this isomorphism between the structures of consciousness
and awareness that constitutes the principle of structural coherence.
This principle reflects the central fact that even though cognitive
processes do not conceptually entail facts about conscious experience,
consciousness and cognition do not float free of one another but
cohere in an intimate way.
This principle has its limits. It allows us to recover structural
properties of experience from information-processing properties,
but not all properties of experience are structural properties.
There are properties of experience, such as the intrinsic nature
of a sensation of red, that cannot be fully captured in a structural
description. The very intelligibility of inverted spectrum scenarios,
where experiences of red and green are inverted but all structural
properties remain the same, show that structural properties constrain
experience without exhausting it. Nevertheless, the very fact that
we feel compelled to leave structural properties unaltered when
we imagine experiences inverted between functionally identical systems
shows how central the principle of structural coherence is to our
conception of our mental lives. It is not a logically necessary
principle, as after all we can imagine all the information processing
occurring without any experience at all, but it is nevertheless
a strong and familiar constraint on the psychophysical connection.
The principle of structural coherence allows for a very useful
kind of indirect explanation of experience in terms of physical
processes. For example, we can use facts about neural processing
of visual information to indirectly explain the structure of color
space. The facts about neural processing can entail and explain
the structure of awareness; if we take the coherence principle for
granted, the structure of experience will also be explained. Empirical
investigation might even lead us to better understand the structure
of awareness within a bat, shedding indirect light on Nagel's vexing
question of what it is like to be a bat. This principle provides
a natural interpretation of much existing work on the explanation
of consciousness (e.g. Clark 1992 and Hardin 1992 on colors, and
Akins 1993 on bats), although it is often appealed to inexplicitly.
It is so familiar that it is taken for granted by almost everybody,
and is a central plank in the cognitive explanation of consciousness.
The coherence between consciousness and awareness also allows a
natural interpretation of work in neuroscience directed at isolating
the substrate (or the neural correlate) of consciousness.
Various specific hypotheses have been put forward. For example,
Crick and Koch (1990) suggest that 40-Hz oscillations may be the
neural correlate of consciousness, whereas Libet (1993) suggests
that temporally-extended neural activity is central. If we accept
the principle of coherence, the most direct physical correlate
of consciousness is awareness: the process whereby information is
made directly available for global control. The different specific
hypotheses can be interpreted as empirical suggestions about how
awareness might be achieved. For example, Crick and Koch suggest
that 40-Hz oscillations are the gateway by which information is
integrated into working memory and thereby made available to later
processes. Similarly, it is natural to suppose that Libet's temporally
extended activity is relevant precisely because only that sort of
activity achieves global availability. The same applies to other
suggested correlates such as the "global workspace" of
Baars (1988), the "high-quality representations" of Farah
(1994), and the "selector inputs to action systems" of
Shallice (1972). All these can be seen as hypotheses about the mechanisms
of awareness: the mechanisms that perform the function of making
information directly available for global control.
Given the coherence between consciousness and awareness, it follows
that a mechanism of awareness will itself be a correlate of conscious
experience. The question of just which mechanisms in the
brain govern global availability is an empirical one; perhaps there
are many such mechanisms. But if we accept the coherence principle,
we have reason to believe that the processes that explain
awareness will at the same time be part of the basis of consciousness.
2. The principle of organizational invariance. This principle
states that any two systems with the same fine-grained functional
organization will have qualitatively identical experiences.
If the causal patterns of neural organization were duplicated in
silicon, for example, with a silicon chip for every neuron and the
same patterns of interaction, then the same experiences would arise.
According to this principle, what matters for the emergence of experience
is not the specific physical makeup of a system, but the abstract
pattern of causal interaction between its components. This principle
is controversial, of course. Some (e.g. Searle 1980) have thought
that consciousness is tied to a specific biology, so that a silicon
isomorph of a human need not be conscious. I believe that the principle
can be given significant support by the analysis of thought-experiments,
however.
Very briefly: suppose (for the purposes of a reductio ad absurdum)
that the principle is false, and that there could be two functionally
isomorphic systems with different experiences. Perhaps only one
of the systems is conscious, or perhaps both are conscious but they
have different experiences. For the purposes of illustration, let
us say that one system is made of neurons and the other of silicon,
and that one experiences red where the other experiences blue. The
two systems have the same organization, so we can imagine gradually
transforming one into the other, perhaps replacing neurons one at
a time by silicon chips with the same local function. We thus gain
a spectrum of intermediate cases, each with the same organization,
but with slightly different physical makeup and slightly different
experiences. Along this spectrum, there must be two systems A
and B between which we replace less than one tenth of the
system, but whose experiences differ. These two systems are physically
identical, except that a small neural circuit in A has been
replaced by a silicon circuit in B.
The key step in the thought-experiment is to take the relevant
neural circuit in A, and install alongside it a causally
isomorphic silicon circuit, with a switch between the two. What
happens when we flip the switch? By hypothesis, the system's conscious
experiences will change; from red to blue, say, for the purposes
of illustration. This follows from the fact that the system after
the change is essentially a version of B, whereas before
the change it is just A.
But given the assumptions, there is no way for the system to notice
the changes! Its causal organization stays constant, so that all
of its functional states and behavioral dispositions stay fixed.
As far as the system is concerned, nothing unusual has happened.
There is no room for the thought, "Hmm! Something strange just
happened!." In general, the structure of any such thought must
be reflected in processing, but the structure of processing remains
constant here. If there were to be such a thought it must float
entirely free of the system and would be utterly impotent to affect
later processing. (If it affected later processing, the systems
would be functionally distinct, contrary to hypothesis). We might
even flip the switch a number of times, so that experiences of red
and blue dance back and forth before the system's "inner eye."
According to hypothesis, the system can never notice these "dancing
qualia."
This I take to be a reductio of the original assumption.
It is a central fact about experience, very familiar from our own
case, that whenever experiences change significantly and we are
paying attention, we can notice the change; if this were not to
be the case, we would be led to the skeptical possibility that our
experiences are dancing before our eyes all the time. This hypothesis
has the same status as the possibility that the world was created
five minutes ago: perhaps it is logically coherent, but it is not
plausible. Given the extremely plausible assumption that changes
in experience correspond to changes in processing, we are led to
the conclusion that the original hypothesis is impossible, and that
any two functionally isomorphic systems must have the same sort
of experiences. To put it in technical terms, the philosophical
hypotheses of "absent qualia" and "inverted qualia,"
while logically possible, are empirically and nomologically impossible.
(Some may worry that a silicon isomorph of a neural system might
be impossible for technical reasons. That question is open. The
invariance principle says only that if an isomorph is possible,
then it will have the same sort of conscious experience.)
There is more to be said here, but this gives the basic flavor.
Once again, this thought experiment draws on familiar facts about
the coherence between consciousness and cognitive processing to
yield a strong conclusion about the relation between physical structure
and experience. If the argument goes through, we know that the only
physical properties directly relevant to the emergence of experience
are organizational properties. This acts as a further strong
constraint on a theory of consciousness.
3. The double-aspect theory of information. The two preceding
principles have been nonbasic principles. They involve high-level
notions such as "awareness" and "organization,"
and therefore lie at the wrong level to constitute the fundamental
laws in a theory of consciousness. Nevertheless, they act as strong
constraints. What is further needed are basic principles
that fit these constraints and that might ultimately explain them.
The basic principle that I suggest centrally involves the notion
of information. I understand information in more or less
the sense of Shannon (1948). Where there is information, there are
information states embedded in an information space.
An information space has a basic structure of difference
relations between its elements, characterizing the ways in which
different elements in a space are similar or different, possibly
in complex ways. An information space is an abstract object, but
following Shannon we can see information as physically embodied
when there is a space of distinct physical states, the differences
between which can be transmitted down some causal pathway. The states
that are transmitted can be seen as themselves constituting an information
space. To borrow a phrase from Bateson (1972), physical information
is a difference that makes a difference.
The double-aspect principle stems from the observation that there
is a direct isomorphism between certain physically embodied information
spaces and certain phenomenal (or experiential) information
spaces. From the same sort of observations that went into the principle
of structural coherence, we can note that the differences between
phenomenal states have a structure that corresponds directly to
the differences embedded in physical processes; in particular, to
those differences that make a difference down certain causal pathways
implicated in global availability and control. That is, we can find
the same abstract information space embedded in physical
processing and in conscious experience.
This leads to a natural hypothesis: that information (or at least
some information) has two basic aspects, a physical aspect and a
phenomenal aspect. This has the status of a basic principle that
might underlie and explain the emergence of experience from the
physical. Experience arises by virtue of its status as one aspect
of information, when the other aspect is found embodied in physical
processing.
This principle is lent support by a number of considerations, which
I can only outline briefly here. First, consideration of the sort
of physical changes that correspond to changes in conscious experience
suggests that such changes are always relevant by virtue of their
role in constituting informational changes - differences
within an abstract space of states that are divided up precisely
according to their causal differences along certain causal pathways.
Second, if the principle of organizational invariance is to hold,
then we need to find some fundamental organizational property
for experience to be linked to, and information is an organizational
property par excellence. Third, this principle offers some
hope of explaining the principle of structural coherence in terms
of the structure present within information spaces. Fourth, analysis
of the cognitive explanation of our judgments and claims
about conscious experience - judgments that are functionally explainable
but nevertheless deeply tied to experience itself - suggests that
explanation centrally involves the information states embedded in
cognitive processing. It follows that a theory based on information
allows a deep coherence between the explanation of experience and
the explanation of our judgments and claims about it.
Wheeler (1990) has suggested that information is fundamental to
the physics of the universe. According to this "it from bit"
doctrine, the laws of physics can be cast in terms of information,
postulating different states that give rise to different effects
without actually saying what those states are. It is only
their position in an information space that counts. If so, then
information is a natural candidate to also play a role in a fundamental
theory of consciousness. We are led to a conception of the world
on which information is truly fundamental, and on which it has two
basic aspects, corresponding to the physical and the phenomenal
features of the world.
Of course, the double-aspect principle is extremely speculative
and is also underdetermined, leaving a number of key questions unanswered.
An obvious question is whether all information has a phenomenal
aspect. One possibility is that we need a further constraint on
the fundamental theory, indicating just what sort of information
has a phenomenal aspect. The other possibility is that there is
no such constraint. If not, then experience is much more widespread
than we might have believed, as information is everywhere. This
is counterintuitive at first, but on reflection I think the position
gains a certain plausibility and elegance. Where there is simple
information processing, there is simple experience, and where there
is complex information processing, there is complex experience.
A mouse has a simpler information-processing structure than a human,
and has correspondingly simpler experience; perhaps a thermostat,
a maximally simple information processing structure, might have
maximally simple experience? Indeed, if experience is truly a fundamental
property, it would be surprising for it to arise only every now
and then; most fundamental properties are more evenly spread. In
any case, this is very much an open question, but I believe that
the position is not as implausible as it is often thought to be.
Once a fundamental link between information and experience is on
the table, the door is opened to some grander metaphysical speculation
concerning the nature of the world. For example, it is often noted
that physics characterizes its basic entities only extrinsically,
in terms of their relations to other entities, which are themselves
characterized extrinsically, and so on. The intrinsic nature of
physical entities is left aside. Some argue that no such intrinsic
properties exist, but then one is left with a world that is pure
causal flux (a pure flow of information) with no properties for
the causation to relate. If one allows that intrinsic properties
exist, a natural speculation given the above is that the intrinsic
properties of the physical - the properties that causation ultimately
relates - are themselves phenomenal properties. We might say that
phenomenal properties are the internal aspect of information. This
could answer a concern about the causal relevance of experience
- a natural worry, given a picture on which the physical domain
is causally closed, and on which experience is supplementary to
the physical. The informational view allows us to understand how
experience might have a subtle kind of causal relevance in virtue
of its status as the intrinsic nature of the physical. This metaphysical
speculation is probably best ignored for the purposes of developing
a scientific theory, but in addressing some philosophical issues
it is quite suggestive.
8 Conclusion
The theory I have presented is speculative, but it is a candidate
theory. I suspect that the principles of structural coherence and
organizational invariance will be planks in any satisfactory theory
of consciousness; the status of the double-aspect theory of information
is less certain. Indeed, right now it is more of an idea than a
theory. To have any hope of eventual explanatory success, it will
have to be specified more fully and fleshed out into a more powerful
form. Still, reflection on just what is plausible and implausible
about it, on where it works and where it fails, can only lead to
a better theory.
Most existing theories of consciousness either deny the phenomenon,
explain something else, or elevate the problem to an eternal mystery.
I hope to have shown that it is possible to make progress on the
problem even while taking it seriously. To make further progress,
we will need further investigation, more refined theories, and more
careful analysis. The hard problem is a hard problem, but there
is no reason to believe that it will remain permanently unsolved.[*]
*[[The arguments in this paper are presented in greater
depth in my book The Conscious Mind (Oxford University Press,
1996). Thanks to Francis Crick, Peggy DesAutels, Matthew Elton,
Liane Gabora, Christof Koch, Paul Rhodes, Gregg Rosenberg, and Sharon
Wahl for their comments.]]
Further Reading
The problems of consciousness have been widely discussed
in the recent philosophical literature. For some conceptual clarification
of the various problems of consciousness, see Block 1995, Nelkin
1993, and Tye 1995. Those who have stressed the difficulties of
explaining experience in physical terms include Hodgson 1988, Jackson
1982, Levine 1983, Lockwood 1989, McGinn 1989, Nagel 1974, Seager
1991, Searle 1991, Strawson 1994, and Velmans 1991, among others.
Those who take a reductive approach include Churchland 1995, Clark
1992, Dennett 1991, Dretske 1995, Kirk 1994, Rosenthal 1996, and
Tye 1995. There have not been many attempts to build detailed nonreductive
theories in the literature, but see Hodgson 1988 and Lockwood 1989
for some thoughts in that direction. Two excellent collections of
recent articles on consciousness are Block, Flanagan, and Güzeldere
1996 and Metzinger 1995.
Published in the Journal of Consciousness Studies in
1995. Reprinted with permission.
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Re: Facing Up to the Problem of Consciousness
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I believe the answer for the hard problem is not so hard, and is found in the following:
1. Image and Objects
By 'image' I call the overall content which is under our attention, at a given moment. This definition includes all data we sense, all thoughts we process, as well as all related data stored in our memory and being accessed at that specific moment. (The image therefore is not related to pictorial data only, but to various types of data, such as voice, smell, as well as ideas, feelings, thoughts.)
An image is composed of objects. An object can represent any portion of an image, and may be composed of other objects. For example, the table in front of us is an object, but each one of its legs can be another object. The picture hanging on the wall is an object, but each one of its details can an object as well. The question of the resolution depends on our attention. If our attention is given to each one of chair legs, then each one becomes an object in our mind. If we look at the picture but not for any specific detail, only the picture as a whole is an object for us.
Objects are stored in our memory, and are the elementary particles composing the memory, its building blocks.
2. Links
An 'object link' is a pointer from one object to another. An object is poiting another object if there is a certain relation between them. To this relation I call 'similarity'. If object A is similar to object B, a link is created by the brain. The similarity occurs if some of the components composing object A exist in B, or partially exists.
The brain tries to match every new object with the inventory of old objects stored in memory. Take for example the case where we perceive a face of a movie actor which seems familiar. After a few moments of fail attempts to recognize the face, the match is taking place (if we are lucky) with a great relief. The constant matching operation is therefore an essence of the brain (along with other essential functions). Think of a music which sounds familiar to you, but you can not recognize it . It is ineviatle for the brain not to try and look for a match with the inventory of music stored in your memory.
When a match takes place, both objects, the old and the new, are being updated with that link. If a new song reminds us an old music, both the song and the old music objects are updated, as a part of the activation process of the old music object. The links therefore is not an independent entity in the space of memory, but embedded within the objects.
The matching operation is not a trivial one. Take the example of solving a mathenatical problem. The process of thinking invloves various objects, but finding the appropriate links is the creative part.
Links has a 'degree of strenght' attribute, where high level of strength represent a closer relationship. The objects stored in memory are sorted according to several keys, enabling fast search and retrieval. The familiar face invokes a search with movies as a primary key, and faces with a secondary key, for example (or vice versa?)
3. Active Objects
By 'active objects' I refer to objects brought into our attention at a given moment, i.e belong to the current image. The image therefore is composed of active objects only. Active object can be a completely new object, brought to our attention as a result of an interaction with the external world via our senses, with our internal world via our feelings, thoughts, etc., or an old object activated from our memory storage. An old object can be activated therefore as a result of a match with a new object, or as a result of a link from another (already activated) old object. A third option would be an activation based on the degree of strength. Sometime an item pops into our attention from our memory without any reasonable association, or we start thinking of an item without any specific reason known to us. In that case, the object is activated because of its relative strength, i.e it is the object with the highest degree of strength for that moment.
The strength of objects gets updated continuously. Each link which is resolved and activates an existing object brings to an update of the object strength. The strength is also a function of the number of links associated with an object, the time passed since the object has been created, and then activated. If we appreciated someone, then what he said about us might be very meaningful and stored with a high degree of strength in our memory. If, after some time, we realise that the amount of appreciation was too high, the strength of that object would significantly decrease.
When an object becomes active, not all of its links are resolved. The links to the strongest objects are being resolved first. The links contain the information of the degree of strength of the objects they are pointing to, so a link does not have to be resolved first, and an object need not be activated first, in order to find out what is its strength. At every moment, the strongest link among all links of all active objects is being resolved. The next activated object (whether a new object or an existing one) will add its inventory of links to the current pool, from which the next strongest link will be resolved. I call this description the 'link resolution algorithm'.
The capacity of the active image is limitted. As long as objects are being activated and added to the image, other objects are dropped from the image. The object with the lowest degree of strength are dropped, and stored in memory.
A key point in the algorithm described below, is that there is no 'selector' that selects the active objects, and determines which links to resolve. There is no need for a manager, for an entity which exists on top of the objects, running the activation process. This is a major fact for the understanding of our consciousness.
4. Consciousness and Self Consciousness
An object that is presented in several images is our body. Our senses perceive our body as a part of the external world, creating a 'body' object. Since it appears again and again, the object becomes stronger, and pointed by a growing number of links. In fact, the body object is activated most of the time, taking a share in most of the temporary images. It becomes a 'framework' for all other objects, a kind of background. Our internal feelings that originate in our body, which also repeat themselves several times, are being added to the body object, enriching its content. The body object (I'll call it the self object) becomes the object with the highest level of strength, and with the largest amount of content, much higher and larger than all other objects.
Whenever the self object is part of the current image, along with another activated object X, we say that we are aware of X, or conscious of X. Consciousness is therefore a state of objects, the relation between the self object and other objects. Consciousness is not an observer, which exists on top of the objects. There is no such observer, because all entities are established as objects, and are all on the same level. The term image is misleading, there is no observer for the current image, for our current awareness. The self is not located above the objects, but aside of them. When we say 'I am conscious of X', that means the self object is conscios of X, that the self object has a relation to X object. The 'I' is the self object, there is no 'I' beyond that.
There are relations between many pairs of activated objects. But only the self object has the level of strength and amount of content that captures our attention.
The self object (as any other object) can initiate other operations, and activate other objects. In case the self is activating itself, as a subject of interest, we call this a self consciousness. Consciousness in general is a reflection, a relation from the self object to another object. In case of being conscious of X, the link is from the self object to X object. In case of self-consciousness, the link is from the self object to itself. END
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Re: Facing Up to the Problem of Consciousness
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Shai_Op,
Perhaps we need to distinguish a "formal framework for consciousness" from the subjective sensation of consciousness. I am not sure which terms should apply to each, and whether the difference is one of degree or something more substantially "different".
Your image-object-linking framework is a fine formalism for approaching the organization of "AI-mind". The description you give could be (and I imagine, has been) codified in object-oriiented languages. In this respect, the "self-object" is the one holding and manipulating the current temporal "image", associates objects to one another, either from external stimuli or from memory, strengthens or weakens associations accordingly.
And if presented with "input" whose processing requires or "leads to" reference to the "self-object", a "self-referential link" is forged or strengthened withing the current image.
Ok. But all of this can be accomplished with a relatively small C++ or Java implementation, and when it runs, and happens to be "entertaining" the self-reference link, do you suppose that this ... "system" is experiencing "conscious awareness" as you or I might experience?
We have a nice clean formal description, and we can implement this in a model. So the system is "formally conscious" (by DEFINITION) when it is entertaining the self-reference link.
Is this the same as the "feeling of consciousness" (i.e., sentient consciousness)?
I think that this is the issue at hand.
Cheers! ____tony b____
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Re: Facing Up to the Problem of Consciousness
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Shai..
Your idea is actually quite similar to an explanation for the mind worked out by one of the pre-Socratic Greek philosophers 2500 years ago. (although he didn't put it in terms of object-oriented programming, obviously.) I can't remember which one it was...Zeno maybe (?)
Anyway, I don't think it answers all the questions about consciousness. For instance, is it possible for us to be aware of something without being conscious of it? This is not just semantics--I've seen research which indicates our body responds to possible danger before we consciously realize what's happening. We have all had the sensation of going on autopilot while doing some routine task...or while driving on the highway. The French existentialist philosopher Sartre gave an example of a man counting the contents of a pack of cigarettes...the task is so boring that the man does it without any thought..until a friend comes up and asks him what he is doing....at that moment, the task comes back into his conscious mind, although, at some level, he was aware of it all the time.
There seems to be several different subroutines operating in the brain at a time. As you indicate, the self-conscious observer is not somehow above and over the rest of the mind, but it is much harder to model than a simple hierarchy of objects.
Although I think that the metaphysical superstructure of Buddhism is quite possibly bogus, one can come to a better understanding of just how complex the conscious mind is by engaging in zazen or another meditative practice regularly. I have yet to see an AI proposal which is subtle enough to deal with all of this--although I would not say that such a program is impossible...just a little farther away than many of us would like.
BC
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Re: Facing Up to the Problem of Consciousness
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>is it possible for us to be aware of something without being conscious of it?
SEEING WHAT YOU DON'T SEE?
Following certain kinds of brain lesions, patients report an inability to see objects, but if pressed to guess at their location they display a capacity to point at them with reasonable accuracy. The phenomenon, called "blindsight", is one of the more dramatic of a number of lines of evidence suggesting that being aware of doing something is distinguishable from doing something, that areas of the brain underlying the experience of doing at least some things are distinct from those needed to actually do those things.
Such a dissociation has a number of interesting implications. In a general sense, it provides evidence for the existence and significance of an "unconscious" as a contributor to human behavior (and hence for "consciousness" as distinctive part rather than synomous with the totality of brain function). Blindsight also provides a possible explanation for some experiences of "magical" or "transcendent" abilities, at least insofar as these relate to performance characteristics of individuals for which the individuals themselves cannot account. A dissociation between unconscious and conscious processing is also of significance in an educational context, since the two sorts of processing may acquire, process, and make use of experiences in different ways.
Blindsight - the ability to respond appropriately to visual inputs while lacking the feeling of having seen them - might be something which only occurs in cases of brain damage, but seems much more likely to be a significant phenomenon of intact brain function as well. Indeed, it seems likely that blindsight (and similar phenomena in other spheres) is an important ingredient of of a variety of activities where one wants to move quickly and appropriately, without "thinking about it".
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Re: Facing Up to the Problem of Consciousness
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I think much (1/2 ?) of the confusion is that the single term "consciousness" is standing-in for too many "related things".
As I wrote much earlier, if I am exploring a cave, and a "tiger" in the distance makes a growling sound, it might not be "loud enough" that I "consciously" sit up and take notice. But the sound still reached my ears, and some part of my neural system "took notice", and as part of its evolved response to such a sound, might start a bit of additional adrenaline flowing through my system, causing my heart to speed up, etc.
I might then become "consciously aware" that my "nervousness" has increased, yet I do not know the exact reason. I might just suddenly feel "spooked".
Another distinction, (perhaps impossible to resolve except, as John B might argue, from "reasonableness") is whether a system with a formal "self-concept" exercised in the course of information processing is ever "feeling conscious" the way you or I experience the feeling. This was my question to Shai_op. The system of "Image-Object-Links", and the growing accumulation of relationships that serve to bolster the "self-concept" may well give rise to an intelligence that "functionally acts as a conscious being". But this is perhaps not the same as "feeling awake" as we experience consciousness.
Thus, we have three (roughly) separable things that might be referred to when someone says "conciousness".
1. The formal "has a programmatic concept of self".
To understand why I feel this is inadequate, Imagine a sophisticated object-oriented software system that is exposed to external "objects" and can access and create new "internal" objects, including the "self-onject", and update link-relations in strengths, etc. All of this is running on a Pentium processsor.
Why not just eliminate the Pentium processor, and conduct all the operations on paper, with crayons? Give me a new object, I seek into "memory" (stack of paper) for related objects, use an abacus to calculate a revised "linkage strength", take out a crayon and update the cell that maintains the "strength" of that link, etc.
The overall system MIGHT behave consistent with having a true self-concept, and indeed, it would thus possess such a "working concept". But MUST the system possess "subjective feeling of awareness" just by this formalism?
Put more simply, note that my "formalism with paper and crayons" involves no "electricity" (per se).
I wonder to what degree the parallel between "neural-electric" and "transistor-electric" lends me to feel that consciousness-feeling must involve a physical "charge-dynamic", which would be lacking in the "pure-paper-analogy".
2. The Human(-like) Conscious Waking State
3. The Human(-like) Subconscious Autonomous State
If we continually confuse these three things, at the outset, by referring to them all as "consciousness", we will get into endless misunderstandings. Better to find three separate names, explore those carefully, and if it turns out that the distinction (in some ways) is needless, let that be a conclusion.
Cheers! ____tony b____ |
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Re: Facing Up to the Problem of Consciousness
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AZ,
I don't know, one way or another, of course.
My diatribe just intends to point out that "we chemical things", having advanced to the point of thoughts where "formal symbol logic" can be "recognized" (perhaps more accurately, constructed), and we employ it so thoroughly in our logical/rational lives, that we begin to use it to "approximate" the analog, the fuzzy, the less-than-Boolean world. Oddly, "logical thought" seems to be nature's latest (most advanced) development, and yet as we embark upon the creation of thinking machines, it turns out to be the easiest to emulate.
Far easier to program software to calculate the "logical deductions" (A > B, and B > C, thus A > C) which humans have only recently formalized, than to program it to appreciate nuances of humor, or the joy of a summer breeze.
The question is whether our human ability to have such appreciations is, in part, due to the physical nature of our construction (chemicals, etc., and of course the complexity of our form), or is it merely the complexity?
Are we akin, purely, to software running on (interchangeable) hardware, or are we the hardware as well? Are the varying ion-concentrations at our neural synaptic sites critical to our (subjective) "feeling of the world", or would an equivalent complexity of glass marbles shifting between chutes in a large glass machine engender the same subjective sensations of "feeling"?
I don't know, one way or the other. But I don't think the answer is arrived at easily, either.
Cheers! ____tony b____ |
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