Unity of Consciousness

When I see you as myself and visa versa, we will understand unity consciousness. It is a recognition of the oneness of all life. So if I work against others, I am not in unity. When I am in unity I see myself as connected to all. In truth, I don’t see myself.

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http://www.scholarpedia.org/article/Unity_of_consciousness

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Curator: Dr. Tim Bayne, University of Oxford

To What Extent is Consciousness Unified?

There is little consensus as to how much unity there is within consciousness. Some theorists hold that consciousness is rarely unified to any considerable degree, others hold that although consciousness is typically unified (in humans at least) this unity can break down in the context of pathologies of consciousness, and still others hold that there is some sense in which consciousness is necessarily unified. Although there are substantive disagreements here, it is difficult to disentangle them from terminological disagreements, for even a cursory glance at the literature reveals that a large number of things have been meant by the claim that consciousness is or is not unified. Some forms of unity can clearly be lost from consciousness, but other forms of unity may be deep, and perhaps even necessary, features of consciousness.

Let us begin with subject unity. There is a sense in which subject unity itself cannot be lost, for conscious states must always be the states of a particular subject of experience. However, there are various pathologies of consciousness in which the subject’s sense of being a unified subject of experience is disrupted. For example, patients suffering from the schizophrenic disorder of thought insertion will describe thoughts as being put into their mind by an alien agency. Certain aspects of the sense of being a unified subject of experience may also be undermined in the depersonalization syndrome, for patients suffering from depersonalization often report that it is as if their experiences are no longer their own.

Pathologies of consciousness also provide us with examples in which aspects of the representation unity of consciousness are compromised. In apperceptive agnosia, the normal experience of objects as unified wholes is lost. Patients experience the various features of visually presented objects, but are unable to synthesize those features into representations of unitary objects. In certain types of out-of-body experience perception may lose the spatial unity that it normally has, for subjects report that they experience the world from discontinuous spatial locations.

What about access unity? Many theories of consciousness take access unity as a kind of theoretical ideal, assuming that once performance limitations of various kinds are taken into account the contents consciousness will be equally available for cognitive and behavioural consumption. It is very much an open question whether this assumption is justified. At the very least, certain experimental findings put pressure on it. We have space here to mention only Marcel’s (1993) results. Marcel presented subjects with a light for 200 ms, and required subjects to report the onset of the light in three ways at once: by blinking, by pressing a button, and by saying ‘yes’. Surprisingly, he found that subjects often gave inconsistent responses. For example, the subject’s positive button-pressing response might be at odds with his negative verbal response.

Perhaps the most intense debate regarding the question of whether consciousness is unified has concerned the relationship between subject unity and co-consciousness. According to one conception of the unity of consciousness, it is not possible for a subject to have simultaneous conscious states that are not co-conscious. Bayne and Chalmers (2003) call this ‘the unity thesis’. Let us examine some objections to the unity thesis. In order to simplify discussion I will assume that subjects of experience are organisms.

One cluster of objections to the unity thesis concern dissociative phenomena such as automatic writing, fugue states and multiple personality (since known as Dissociative Identity Disorder). These phenomena received detailed examination by Alfred Binet, William James and Morton Prince in the 19th century, and were commonly thought to show that “in certain persons, at least, the total possible consciousness may be split into parts which coexist but mutually ignore each other” (James 1890: 206). The tradition of appealing to dissociative phenomena as evidence against the claim that consciousness is necessarily unified continued into the 20th century, with Ernest Hilgard arguing that the unity of consciousness is lost under hypnosis. However, the interpretation of these syndromes is extremely challenging (see Braude 1995). It is clear that dissociation involves various kinds of representational and access disunities, but it is debatable whether it ever involves the simultaneous existence of two separate streams of consciousness in a single subject (Bayne 2007).

Since the 1970s, discussion of the unity of consciousness has been dominated by the commissurotomy (or split-brain) syndrome. The split-brain operation involves sectioning the corpus callosum in order to treat epilepsy. Although the procedure has little impact on cognitive function in everyday life, carefully controlled research seems to show that split-brain patients have a divided consciousness, at least in certain environments. In a typical split-brain experiment, the word ‘key-ring’ might be presented so that ‘key’ falls within the patient’s left visual field and ‘ring’ falls within the patient’s right visual field. The contralateral structure of the visual system ensures that stimuli projected to the left visual field are processed in the right hemisphere and vice-versa. When asked to report what she sees the patient will say that she sees only the word ‘ring’, yet, with her left hand the patient may select a picture of a key, ignoring pictures of a ring and a key-ring.

Many theorists endorse the two-streams model of the split-brain, according to which split-brain patients have two streams of consciousness, one in each hemisphere (e.g. Sperry 1984). It is this duality of consciousness which is thought to explain: (i) why the patient appears to have a conscious representation of ‘key’ and ‘ring’ but no representation of ‘key-ring’; and (ii) why the patient’s representation of ‘key’ and ‘ring’ are available to different consuming systems. Two-streams accounts of the split-brain are well-equipped to explain the behavioural disunity that patients exhibit in laboratory conditions, but they struggle to account for the unity that split-brain patients exhibit in everyday situations. Some two-stream theorists attempt to explain this unity by adopting the duplication gambit, according to which the split-brain patient has behavioural integrity because their two streams of consciousness have the same contents (Davis 1997; Moor 1982). Other two-streamers hold that the patient’s stream of consciousness is normally unified and divides into two only in laboratory conditions (Marks 1981; Tye 2003).

Another model of the split-brain holds that such patients have a fragmented stream of consciousness, in that they have triples of conscious states (e1, e2 and e3) such that e1 and e2 are both co-conscious with e3 but not with each other (Lockwood 1989). This model attempts to account for both the unity and disunity exhibited by split-brain patients. However, as we noted above, it is controversial whether consciousness can fragment in this way.

A third model of the split-brain holds that consciousness in the split-brain switches between hemispheres (Bayne 2008). A central line of evidence for this approach derives from research conducted by Levy (1977) and Trevarthen (1974) involving chimeric stimuli (that is, similar stimuli joined at the vertical mid-line). Since each hemisphere receive information about a different stimulus one would expect the subject to produce conflicting responses if both left-hemisphere and right-hemisphere representations were conscious, but no such conflict was observed. Patients gave one response on the vast majority of competitive trials, and the non-responding hemisphere gave no evidence that it had any perception at all. In light of these findings, one might suppose that consciousness in the split-brain ‘switches’ between hemispheres, and that at any one time the split-brain patient has but a single stream of consciousness. If this model is correct, then perhaps consciousness is always unified, even in those human beings in whom the corpus callosum has been severed.
Explaining the Unity of Consciousness

Of the many complex issues surrounding the unity of consciousness, explanatory issues are arguably the most obscure. Perhaps the only point that is clear is that we should not be looking for a single explanation of the unity of consciousness: not only are there different forms of the unity of consciousness, particular types of unity might demand a variety of explanations. As Hurley points out, the unity of consciousness might demand both personal and sub-personal levels of explanation (Hurley 1998).

The task of explaining object unity has been pursued under the heading of the binding problem: what is it that binds the various experiential features of an object together into a representation of a unitary object (Revonsuo 1999; Triesman 1996; 2003)? There is at present no-consensus as to how the binding problem ought to be solved; indeed, there is little consensus about the nature of the problem itself. It is also controversial whether the binding problem might be related to wider questions concerning consciousness itself. Although it has often been assumed that the mechanisms of object binding are intimately related to the mechanisms responsible for consciousness itself, convincing arguments for this claim are rather thin on the ground.

What about co-consciousness? How might we explain why it is that a person’s simultaneous experiences are usually (if not always) mutually co-conscious? Here it is useful to contrast atomistic theories of consciousness with holistic theories of consciousness. Current theories tend to take an atomistic or ‘building block’ (Searle 2000) approach to consciousness. Rather than account for the subject’s entire phenomenal field at once, they account for only particular conscious states—a pain, a visual experience, a conscious thought—on a case-by-case basis. Atomistic accounts of consciousness posit one mechanism responsible for making mental states conscious and another for making them co-conscious. There is no shortage of proposals for what the first mechanism might be, but theorists have been noticeably reluctant to tackle the question of what might bind experiential states together. Note, importantly, that this kind of binding problem is distinct from the content-based binding problem discussed in the previous paragraph. Instead of positing one mechanism responsible for consciousness and another that is responsible for the unity of consciousness, holistic theorists invoke a single mechanism responsible for both making mental states conscious and unifying them. According to such models, consciousness is created as a single global state of which the various conscious states—bodily sensations, thoughts, perceptual states, affective states, and so on—are components or abstractions. There are various ways in which the holistic approach might be developed. Accounts of consciousness that posit some form of centralized consciousness module or workspace are most naturally understood in holistic terms. One particularly appealing approach looks to the domain-general enabling mechanisms that are involved in mediating the transition from unconsciousness to consciousness. Perhaps such systems not only enable the creature to be consciousness but also play a role in ensuring that its conscious states will be unified.

The debate between atomistic and holistic approaches to consciousness is very much a live one. In large part, the plausibility of each approach turns on just how common breakdowns in co-consciousness are. Atomism would be buoyed if such breakdowns are common, for holistic approaches struggle to explain how a subject’s conscious states could be conscious without being conscious together. On the other hand, the prospects of holism would be advanced such breakdowns do not occur (or are exceedingly rare), for the absence of phenomenal disunity is precisely what one would expect were consciousness to have a fundamentally holism structure. Not surprisingly, debates about how best to explain the unity of consciousness cannot be separated from debates about the degree to which consciousness is unified.

The issues raised by the unity of consciousness cluster around three headings. What forms can the unity of consciousness take? To what degree is consciousness unified? How might we explain the unity of consciousness?