Why consciousness

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 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. 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 4 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. 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 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.

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 ; see also Crick This theory centers on certain 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. 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? 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. The second example is an approach at the level of cognitive psychology. This is Bernard 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 , 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 is largely directed at explaining the reportability of certain mental contents. The "intermediate level" theory of Jackendoff 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. 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 manifests 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. 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.

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 and Jackendoff 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. 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 ; 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. How does the passing around of electrical and chemical signals between neurons result in a feeling of pain or an experience of red?

There is growing suspicion that conventional scientific methods will never be able answer these questions. Luckily, there is an alternative approach that may ultimately be able to crack the mystery. Things have changed a lot, and there is now broad agreement that the problem of consciousness is a serious scientific issue.

But many consciousness researchers underestimate the depth of the challenge, believing that we just need to continue examining the physical structures of the brain to work out how they produce consciousness. The problem of consciousness, however, is radically unlike any other scientific problem.

One reason is that consciousness is unobservable. If we were just going off what we can observe from a third-person perspective, we would have no grounds for postulating consciousness at all. Of course, scientists are used to dealing with unobservables.

Electrons, for example, are too small to be seen. But scientists postulate unobservable entities in order to explain what we observe, such as lightning or vapour trails in cloud chambers. But in the unique case of consciousness, the thing to be explained cannot be observed. We know that consciousness exists not through experiments but through our immediate awareness of our feelings and experiences. So how can science ever explain it? When we are dealing with the data of observation, we can do experiments to test whether what we observe matches what the theory predicts.

In my view, the only theory that holds up to scrutiny is panpsychism. When I studied philosophy, we were taught that there were only two approaches to consciousness: either you think consciousness can be explained in conventional scientific terms, or you think consciousness is something magical and mysterious that science will never understand. I came to think that both of these views were pretty hopeless. I think we can have hope that we will one day have a science of consciousness, but we need to rethink what science is.

Panpsychism offers us a way of doing this. Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook. Gareth, a Pulitzer prize-winning journalist, is the series editor of Best American Infographics and can be reached at garethideas AT gmail.

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