Hidden Minds (24 page)

With respect to the original programme of split-brain research, Sperry concluded that surgery had left split-brain patients with ‘two separate spheres of consciousness’. But to some degree, all human beings must possess two spheres of consciousness. The surgeon’s knife merely emphasised existing partitions. Underlying all experience is a divisible neurophysiology This suggests that the faculties of the mind are predisposed to separate more readily along certain biological fault lines: reason from intuition, unconscious emotion from conscious emotion, and so on. Moreover, the two hemispheres of the brain are so differently endowed, they might almost be construed as possessing distinct personalities. In the split-brain literature we witness the curious spectacle of contemporary neuroscience revisiting the nineteenth-century world of alter egos – Dostoevsky’s
The Double,
Stevenson’s
Jekyll and Hyde.

But to what extent is such speculation valid?

In an article called ‘The split brain in man’ (1967), Gazzaniga wrote:

Clearly, a definitive demonstration of two independent spheres of consciousness in the same cranium is made somewhat difficult by the absence of language in the right hemisphere. If the right hemisphere possessed the ability to express an opinion (however crudely) that differed from the left hemisphere, the argument for an underlying physiological basis for dipsychism would be considerably more compelling. The experimental requirement was a split-brain subject whose right hemisphere possessed significant language skills. Luckily, just such a subject appeared.

The patient, known as PS, was a sixteen-year-old boy who had been given a commisureotomy – severing the corpus callosum and separating the brain hemispheres – in 1975. Again, this was performed to treat his epilepsy. In order to ask PS’s right hemisphere questions an elaborate experimental design was required. This was because spoken questions, unlike visual images, cannot be delivered to one or other hemisphere. The pathways that subserve the processing of auditory stimuli relay information to both hemispheres. Nevertheless, through an ingenious combination of spoken and visual presentations it was possible to pose a question to one or other of PS’s hemispheres. Although PS’s right hemisphere could not speak, it could express itself by arranging letters.

The results of the subsequent experiments were astonishing. It transpired that PS’s right hemisphere could disagree with his left on a range of topics, from the mundane – such as colour preference – to more complex personal matters. The most dramatic demonstration of hemispheric independence occurred when PS was asked what occupation he intended to pursue after graduation. His left hemisphere wanted to be a draughtsman, but his right hemisphere wanted to be a racing driver.

A further interesting feature of PS’s psychology was that his mood varied according to how well his two hemispheres were ‘getting on. Such a finding is curiously consistent with Freudian and Jungian ideas that equate psy-chopathology with conflict between mental agencies.

Recent scanning studies have also revived another psychoanalytic idea; namely, that early traumatic experiences can divide the psyche. Work undertaken at McLean’s Hospital (a psychiatric centre affiliated to Harvard Medical School) has demonstrated that children who have been neglected or abused show a reduced corpus callosum size. On average, it is up to 40 per cent smaller, A consequence of this might be that the locus of brain activity mediating personality becomes relatively isolated in each hemisphere. Eventually, this might result in the development of two quite different facets of personality, either of which might become dominant in a given circumstance. For example, the McLean team have suggested that recollections of abuse will produce an emotional state signalling a predominance of activity in the right hemisphere.

If the principal pathway of communication between left and right hemispheres of the brain is compromised in abused children, then such individuals might enter adulthood resembling split-brain patients. An ordinarily articulate individual might find it difficult to find words when recollections of abuse have shifted the locus of brain activity into the right hemisphere. The vocabulary and linguistic skills of the left hemisphere might become less accessible – the result of which would be the emergence of what might appear to others to be a secondary personality.

Further evidence for a form of dipsychism rooted in hemispheric asymmetry comes from a bizarre neurological phenomenon known as
alien hand,
in which the non-dominant hand – usually the left – seems to be under the control of a mischievous alter ego. Alien hand occurs in individuals who have suffered a brain injury affecting the motor cortex or, predictably, the corpus callosum. Needless to say, the phenomenon has also been observed in split-brain patients.

The degree to which an alien hand can operate independently can be quite dramatic. For example, items can be selected while shopping that the buyer has no interest in. It is also typical for alien hands to ‘behave’ in a contrary fashion, reversing the actions performed by the dominant hand. For example, unbuttoning a shirt that has just been done up or, even worse, pulling down trousers that have just been raised.

It is customary for neurologists to underplay the psychological significance of alien hand phenomena. The accepted view is that the behaviour is akin to an unwelcome reflex. Nevertheless, it is tempting to endorse an obvious and less pedestrian explanation; namely, that damage to the corpus callosum allows an ordinarily incapacitated and unconscious alter ego to make its presence felt. Like an actor in a low-budget horror movie the unfortunate victim is – at least in part – taken over.

The opposite of alien hand is a neurological condition known as
neglect.
This is when brain injury results in a curious attentional problem in which everything to the left or right is simply ignored. It is as though one or other of the two hemispheres loses the ability to concentrate and retires from active service. Patients suffering from neglect might only eat half the food on their plates, only comb half their hair, or only manage to dress half their bodies. Moreover, they may only be able to turn left or right and, when initiating an action, may forget to engage half of their limbs.

Advances in brain-scanning technology have allowed neuroscientists to actually peer into the working brain. Typically, brain scans produce images in which areas of activity are shown by bright patches of colour. These bright patches represent physical changes such as increased blood flow or consumption of oxygen or glucose.

Scans of patients suffering from neglect show that the visual cortex is functioning normally. Although they are not conscious of stimuli presented in the blind half of their visual field, the information is certainly being processed.

These results would have been of considerable interest to cognitive psychologists conducting experiments on attention on the 1950s. Neglect patients exhibit an extreme and special form of ‘not paying attention’. Modern brain scans convincingly demonstrate that unattended information is being analysed, if only for its basic physical features.

Brain-scanning technology has provided evidence for an even more dramatic demonstration of information processing in the absence of awareness. Recently, a patient in a coma was shown photographs of familiar faces (by retinal projection). The scan revealed activity in cortical regions that ‘light up’ when faces are shown to the conscious brain. Clearly, even in the complete absence of awareness, the brain is capable of undertaking a feature analysis. And given that some patients are sometimes roused from comas by the sound of a familiar voice, who can really say to what degree the ‘inert’ brain is not capable of a more sophisticated, semantic analysis?

Perhaps the most celebrated example of unconscious perception is the phenomenon now known as
blindsight.
As the starkly oxymoronic name suggests, blindsight refers to the accomplishment of tasks associated with being sighted by people who, given their injuries, should be blind. The phenomenon has a relatively long history. For many years people working in close proximity with the blind had observed instances of oddly competent behaviour (for example blind individuals who seemed to have an uncanny knack of being able to side-step obstructions which would otherwise have caused them to trip over) and in the First World War blinded soldiers were reputed to have avoided ordnance by ducking – even though they seemed to have no idea what they were doing,

Blindsight only occurs in individuals whose blindness is due to damage affecting the visual cortex. The eyes must be unharmed. Thus, in cases of cortical blindness, visual information arrives for processing at the visual cortex but a conscious representation cannot be constructed. Cortical blindness can be total (where the entire visual cortex is damaged) or partial (which arises when a limited area of the visual cortex is damaged). In the latter case, one or several islands of blindness mottle the visual field.

The first person to undertake a systematic investigation of blindsight was Oxford psychophysiologist Larry Weiskrantz. In the early 1970s he began studying a patient who had sustained damage in an area of the visual cortex known as the right calcarme fissure. The result was that the patient was unable to see anything in the left half of his visual field.

Weiskrantz seated him in front of a screen on which different stimuli were presented – although all on the left. The patient was instructed to reach out and touch the screen when something appeared. This was, of course, a seemingly bizarre instruction, given that the patient couldn’t see anything. Nevertheless, he co-operated -just guessing.

It transpired that the patient’s guesses were remarkably accurate (which was as surprising to him as it was to Weiskrantz). Refining the procedure, Weiskrantz established that, although cortically blind, his unusual subject could indicate the position of a light flash, discriminate correctly between horizontal, vertical, and diagonal lines, and between the letters X and 0, All presented in ‘blind’ regions of the visual field. The patient insisted that he had no awareness of the stimuli; however, he did admit to sometimes experiencing a ‘feeling’ that ‘something was there’.

Since the early days of blindsight research more subjects have been examined and scanning technology has permitted a closer look at underlying mechanisms. Indeed, brain scans have shown that, although the principal area of the visual cortex does not ‘light up’ during blindsight, another small area – known as V5 – does. This is an area concerned with the detection of movement. It would seem, then, that images presented in blind areas do receive a very basic analysis; however, this analysis is not sufficient to produce conscious representations. Even so, a registration of some kind does occur, facilitating the production of relatively accurate ‘guesswork’.

The concept of the cognitive unconscious that emerged during the 1980s – that is the concept described by the likes of John Kihlstrom and described in
Chapter 6
– hinges on the notion of progressive automation. Thus, consciousness might be needed to co-ordinate and assemble a new behaviour (be it mental or physical), but with practice, diminishing resources are required. Once again, brain-scanning technology has exposed this process taking place.

For example, on certain language tasks (such as matching verbs with nouns), scanning investigations show a burst of activity affecting many disparate areas of the brain; however, within a few repetitions, areas of illumination shrink dramatically. Moreover, the areas of the brain associated with higher-order functioning – i.e. those that co-ordinate and supervise more simple processing areas – disappear altogether. One can actually observe the transfer of conscious to preconscious processing; the brain’s habitual inclination to abbreviate everything.

These results are entirely consistent with the theoretical justification of the division between conscious and unconscious minds. If the brain can swiftly reduce tasks to ‘habits’, then more processing resources can be allocated for the analysis of ongoing environmental contingencies. In other words, the brain is in a better position to make plans, deal with new problems, and thus increase its own chances of survival.

Scanning investigations showing the brain converting conscious mental procedures into unconscious mental procedures demonstrate an appealing symmetry. Libet suggested that it takes the brain half a second to raise an event into consciousness. Brain-scanning studies show traffic flowing in the opposite direction. Although it may take somewhat longer, the brain is equally adept at lowering the contents of awareness into the unconscious. Automation is simply the conscious mind going unconscious.

In Freud’s major 1915 essay The unconscious’ he argued that physical theories of the unconscious represented something of a cul-de-sac. Neuroscience was insufficiently advanced to examine or explain the unconscious in terms ofthe physical characteristics ofthe brain. Since 1915 advances in neurosurgery, electroencephalography, and brain scanning have removed most ofthe limitations that turned Freud from a neurologist into a psychologist.

Although brain science and psychology are often and quite perversely presented as oppositional disciplines, they are, in fact, simply different ways of describing mental phenomena. Interestingly, contemporary methods of investigating the brain have not invalidated Freud’s psychological unconscious; they have, if anything, added weight and depth to its foundations. Libet’s EEC studies have gilded Freud’s claim that free will is something of an illusion, and the subcortical structures that process information unconsciously are also those that generate our most id-like emotions. Scanners have penetrated the cerebrum and illuminated the dreaming mind. We can actually see the visual cortex constructing hallucinatory visions and the auditory cortex hallucinatory voices. Moreover, as dreams become nightmares, we can observe the deep structures that mediate fear flaring up like warning beacons. And all the time, while the dream is being orchestrated by subcortical structures and the sensory apparatus, the frontal regions of the brain -essential for testing the tensile strength of reality – glow with a much duller light. Just as the nineteenth-century opium addicts suggested, the conscious mind is anaesthetised, and must bare mute witness to the products of preconscious processing.