Hidden Minds (23 page)

Nevertheless, critics have continued to argue that Libet’s position is untenable insofat as his findings do not correspond with everyday experience. If you accidently touch a hotplate with your finger, it doesn’t take you half a second to pull away, [f a child jumps out in front of a car, it does not take half a second for the driver to hit the brake pedal. How, then, does Libet explain such phenomena? In actual fact, he doesn’t have to. Such questions are fundamentally flawed, confusing behaviour with consciousness. Human beings frequently react in under half a second to environmental demands, but such reactions are not accompanied by consciousness. Rapid reactions usually occur automatically, with consciousness arriving late. It would be extremely unusual to experience awareness of a burning sensation while one’s finger was still in contact with a hot object. The finger has always been withdrawn by the time one is first aware of being burned. If anything, a moment’s reflection on the actual experience of performing rapid reactions seems to reinforce rather than weaken Libet’s position. Preconscious processing routinely influences behaviour in under half a second. In such circumstances, the role of consciousness is not to initiate action, but to make sense of it. Consciousness is like a forensic scientist who must necessarily appear at the scene of the crime after the event in order to collect evidence and draw conclusions.

The late arrival of consciousness can also be observed directly on waking from dreamless sleep. It is sometimes possible to recall an odd state of wakefulness – lasting approximately half a second – that precedes the appearance of identity. We seem to exist only as a primitive, neutral awareness, without autobiography. True consciousness must necessarily involve a sense of self, which presumably cannot be constructed in under half a second. Consequently we are able to experience work in progress – where the ‘work’ in question is ourselves.

A further aspect of Libet’s work which deserves underscoring is that it decisively demonstrates the independence of registration and conscious representation. It is possible to stimulate the brain, confirm that something has been registered by inspecting the EEG, and then abort the process before conscious representation has been achieved. This is an important finding, as it suggests that low levels of stimulus intensity – as might be employed in subliminal perception studies – are probably strong enough to register in the brain without a corresponding event in consciousness. One of the principal arguments against subliminal perception has been that stimuli presented at intensities too low for conscious representation are simply not registered by the brain. Libet’s work strongly suggests that this criticism is invalid.

Although Libet and Freud undertook very different enquiries into the nature of mental life, and employed very different methods, they arrived at similar (if not the same) fundamental conclusions: the exercise of free will is probably an illusion and the real determinants of human behaviour are unconscious. Because free will is such a cherished concept, Libet’s findings were welcomed with the same chilly reception that had previously been reserved for Freud.

Libet has attempted to preserve some dignity for the human race by suggesting that his work does not dispose of free will entirely. For example it is possible to inhibit a behavioural response, even if the early stages of preconscious processing that will eventually engender that response have already been initiated; however, the power to veto decisions is a very diluted form of freedom and reflects, perhaps, an obligation felt by Libet to offer a shred of consolation to disgruntled humanity. The fact remains, if Libet’s work provides an accurate picture of how brain activity and consciousness are related, we are constantly being hoodwinked by the unconscious into believing in a non-existent liberty.

Libet’s early work proved that a concept associated with nineteenth-century psychology – the unconscious – could be profitably investigated within the framework of contemporary neuroscience. Within a few years another research programme was underway which would perform a similar feat with respect to the equally dated concept of dipsychism (i.e. belief in a secondary, unconscious ego).

The human brain has two hemispheres. Although they look the same, and contain identical structures, they are, in fact, differentially endowed. This asymmetry first became apparent through observation of patients suffering from localised brain damage. Injuries to the left side of the brain tend to affect linguistic ability whereas injuries to the right side of the brain tend to affect spatial ability (for example understanding diagrams or pictures). This asymmetry is sometimes – but by no means always – reversed in left-handed individuals.

The rough division of functioning observed in clinical settings was soon confirmed in the laboratory – and later refined. It seems that the left hemisphere is specialised with respect to the comprehension and expression of language and the performance of tasks requiring detailed analysis and logic. The right hemisphere is specialised with respect to processing visual and spatial information, but it is also equipped to perceive holistically. The right hemisphere may also possess abilities that could be described as intuitive.

The two hemispheres of the brain are connected at several points, but the most significant connection consists of a thick band of nerve fibres called the
corpus callosum.
The corpus callosum seems to be the principal conduit through which information is exchanged between hemispheres. In effect, it allows the two hemispheres to converse. Unfortunately, in certain forms of epilepsy, the corpus callosum also serves as a convenient bridge, facilitating the passage of abnormal electrical activity from one side of the brain to the other.

Such patients can benefit from an operation known as a
commisurotomy,
which involves severing the corpus callosum. This procedure confines abnormal electrical activity to the diseased hemisphere (thus diminishing or abolishing seizures). Between 1962 and 1968 nine successful commisurotomies were performed by Los Angeles neurosurgeons Philip Vogel and Joseph Bogen.

At first sight, Vogel and Bogen’s patients seemed completely unchanged apart from the obvious improvement in their health. Even though the two hemispheres of the brain had been disconnected, these patients showed no loss of intelligence and no other signs of brain damage; however, they
were
changed. They now exhibited some subtle and curious processing characteristics that could only be observed in special laboratory conditions. Moreover, these processing characteristics were so unusual that some fundamental assumptions concerning the unity of consciousness were substantially challenged.

In order to appreciate fully the experimental procedures employed to study ‘split-brain’ patients it will be necessary first to describe some basic features of cerebral physiology.

The ‘wiring’ of the visual system is quite complex. Each side of each eye transmits visual information through nerve pathways to both sides of the cerebral cortex. The net result is that if you stare straight ahead, everything to the right goes to the left hemisphere and everything to the left goes to the right hemisphere. All visual information is then shared by transmission through the corpus callosum. This of course does not happen in split-brain patients. Providing they keep their eyes fixed on a point straight ahead, all the information from the left and right sides of the visual field will remain isolated in respective hemispheres.

The wiring that subserves physical movements is less complicated. The body is simply cross-wired in a straightforward manner. Thus, the left hemisphere controls the right side of the body and the right hemisphere controls the left side of the body.

With these facts in mind, we can now consider the remarkable set of experiments conducted by psychobiologist Roger Sperry and his colleagues at the California Institute of Technology. They were conducted on Vogel and Bogen’s split-brain patients, all of whom were right-handed and showed conventional patterns of hemispheric asymmetry (i.e. their speech was located in the left hemisphere and their visuo-spatial abilities in the right hemisphere).

Patients were instructed to look straight ahead while visual information (i.e. words, drawings, and pictures) appeared very briefly on the right or left side of a display screen. Thus, stimuli appearing on the right were conveyed to the left hemisphere and images appearing on the left were conveyed to the right hemisphere. Each image only appeared for a twentieth of a second, which is long enough to ensure conscious registration but not long enough for the eyes to shift. If the eyes were allowed to move then this would result in stimuli being registered in both hemispheres. Sperry’s interest was in how patients would respond to different stimuli presented exclusively to one or other side of the brain. Patients could respond verbally, or with their hands (although both hands could be hidden under a screen).

If a word was flashed to the left hemisphere patients could say what it was and write it with their right hand; however, if a word was flashed to the right hemisphere the patient could neither say what it was nor write it. This was a dramatic confirmation of how processing abilities are asymmetrically distributed in the brain – with language being located exclusively in the left hemisphere. Nevertheless, it was subsequently established that although the right hemisphere is mute, it can still recognise objects. Moreover, if provided with a method of communication that does not involve speech, it will make a correct identification without difficulty.

If a picture of an object, say a fork, was flashed to the right hemisphere and the left hand allowed to feel for a fork among many different objects, a correct identification was accomplished more or less immediately. Even so, having correctly identified the fork, patients could still not say what it was. If, however, the fork was then transferred from the left to the right hand (permitting the left hemisphere to make a contribution) patients were able to say ‘fork’.

As predicted from clinical observations, the right hemisphere proved superior to the left hemisphere when tasks required visual and spatial processing. For example, arranging blocks and drawing cubes was achieved more competently with the left hand than the right, even though the patients were right-handed.

Sperry’s results demonstrated that the corpus callosum was the means by which the two hemispheres of the brain exchanged knowledge – straightforward facts about the world. But what about emotional information? Did emotional information use the same channel?

Although the corpus callosum is severed in split-brain patients, the two hemispheres are not entirely disconnected. Beneath the corpus callosum another pathway – the
anterior commissure
– is preserved. These fibres evolved in the brain much earlier than the corpus callosum, and connect the structures located deeper in each hemisphere described collectively as the
limbic system.
The limbic system is associated with the processing of emotionally significant information, but not directly involved in representing such information in awareness. Expressed more simply, the limbic system operates unconsciously.

The response of split-brain patients to emotional stimuli was explored largely by neuroscientists Michael Gazzaniga and Joseph Le Doux. The results of their research programme suggest that emotional information flashed to the right hemisphere can provoke an emotional response that the left hemisphere experiences, but cannot explain. For example, when the image of a nude woman was flashed to the left hemisphere of a female patient, she laughed and correctly identified the image; however, when the same image was flashed to the right hemisphere the patient claimed to have seen nothing, but proceeded to chuckle anyway. When asked what she was laughing at, she said that she didn’t know, and implicated the experimental apparatus, saying: Oh – that funny machine’. Such responses suggest a curious state of knowing, yet not knowing.

With the aid of specially designed contact lenses it became possible to expose stimuli for longer periods of time without risking information being registered in both hemispheres. Subsequently more powerful and complex emotional material could be used. Films of a disturbing scene shown to the right hemisphere could not be described, yet they reliably evoked feelings of fear and distress. Similarly, films of emotionally pleasurable scenes aroused congruent emotions, but were experienced as equally inexplicable to the patient.

These results indicate that pathways exist in the brain for the transmission of ‘emotion’, across the anterior commissure, from right to left hemispheres; however, in the absence of the more sophisticated transmission route of the corpus callosum, the left hemisphere is not equipped with sufficient knowledge to understand why the emotion has arisen. An everyday phenomenon that might reflect this experience is the appreciation of art. Many people respond viscerally to abstract works such as those by Mark Rothko and Jackson Pollock. The visual pattern is processed in the right hemisphere, but because there is no obvious meaning to communicate to the left hemisphere only an emotional response is produced. Apart from those with special knowledge of art, most people are familiar with the experience of being able to express unequivocal pleasure when viewing a painting while at exactly the same time being unable to say why. If pressed, one might ‘make up’ a reason – but ultimately such a reason can only be a post-hoc rationalisation. Interestingly, split-brain patients do much the same thing.

Gazzaniga and Le Doux noticed that their split-brain subjects were inclined to confabulate after emotional responses had been evoked by right-hemisphere presentations. Although they had no idea why they were feeling scared or happy, they would happily proffer an explanation. Such explanations were, of course, inaccurate; however, the ease with which they were generated suggested a further function of the left hemisphere – namely, to help shore up an illusory sense of authority. This function could represent yet another Orwellian process that helps human beings to accommodate anomalous experiences that must necessarily arise when a part (or parts) of the mind operate independently.