Roger Sperry

Physiologist and psychobiologist Roger W. Sperry was born in Hartford, Connecticut in August 1913 and lived until 1994.

He was educated at various American universities and received qualifications in English, psychology and finally zoology (his doctorate). For his lifelong research into biology and psychobiology he received numerous awards, culminating in the Nobel Prize in Physiology or Medicine in 1981.

It was for his psychological experiments that he received his Nobel Prize, although he also carried out extensive research into physiology, particularly neurological function in animals.

During his career he occupied positions at universities across America, including Harvard, Chicago and the California Institute of Technology. He was married and had two children.

Sperry is best remembered for a series of ingenious experiments into language lateralization in the brain. In order to test differences in the linguistic capabilities of the left and right cerebral hemispheres, he used patients who had undergone a commissurotomy - a removal of the corpus callosum, the part of the brain that allows the hemispheres to communicate with each other. (This was once a common, and reasonably effective, treatment for epilepsy.)

When a visual stimulus is perceived, the information travels initially to one hemisphere only - the left hemisphere if the stimulus is in the right visual field, and vice-versa. In normal brains, the hemispheres freely exchange the information they receive, so this is insignificant. Split-brain patients, as they are known, cannot exchange information between the hemispheres, although they make up for it in everyday life by moving their eyes or head so that stimuli are "seen" by both hemispheres. In Sperry's early experiments, such patients were very briefly shown a word in one visual field or the other, so that the patient had no time to get the other hemisphere to see it. If the word was shown in the right visual field, and thus seen by the left hemisphere, the participant would report seeing it. Clearly the left hemisphere was able to recognise and articulate words. But if it was shown in the left field, and seen by the right hemisphere, the participant would not report seeing anything. Sperry concluded that the right hemisphere of the brain cannot articulate speech; the participants could speak with their left hemisphere only.

However further research showed that the right hemisphere, although language-subordinate, does have some linguistic capabilities. In a follow-up experiment, the initial conditions were replicated except that now, the split-brain patient had their left hand, which is controlled by the right hemisphere, placed behind a screen in a tray containing various objects. They were again shown a word in their left visual field, so that it was picked up by the right hemisphere. This word, a noun, corresponded to one of the objects in the tray. When the word was shown, the participant's left hand would emerge from behind the screen holding the very object indicated by the word. But when asked, the participant claimed not to have seen any word at all and had no idea why their left hand was picking things up.

What was going on? The right hemisphere, which had sole knowledge of the word seen, was indicating its recognition of the word by getting the left hand (the right brain controls the left body and vice-versa) to pick up the object. But if the person was asked to verbally explain what they were doing, only the left hemisphere could take on the job because the right cannot actually speak. The left hemisphere had no idea that any word had been seen, so the participant - bizarrely to anyone who didn't understand what was going on - was unable to claim anything but ignorance of a word he quite clearly had seen. In effect, "split-brain" patients have two brains.

Sperry had thus established that the hemispheres of the brain have their own levels of linguistic competence and that when someone speaks, it is in fact only one half of their brain that does the speaking. People with normal brains, of course, do not notice this because their hemispheres can freely communicate. Split-brain patients on the other hand can get into confusion if they don't allow both hemispheres separate access to the visual information being received.

Further experiments continued the study of language lateralization. In one study, participants were shown different stimuli simultaneously in each visual field. If the subject was asked to draw with their left hand (out of sight) what they had seen, they would draw what been shown on their left, but if asked what they had drawn, would say it was the stimulus shown on their right. Another experiment found that if someone felt an object with their left hand only, the left hand could recognise it again, but the right could not, and the subject couldn't name the object.