Aims

1. Sperry set out to find out which cognitive functions are linked to each hemisphere.
2. He also set out to record the behavioural, neurological and psychological effects of the surgery itself.

Procedure

1. There were 11 patients, all of whom had the corpus callosum severed to treat severe epilepsy.
2. Nine of them had had the surgery recently and two had had it some time before.
3. The apparatus tested the right and left halves of the visual field separately or together, and tested the right and left hands and legs with vision excluded.
4. Each stimulus was projected to the left or the right visual field for one tenth of a second, too fast for the eye to move and carry the image across to the other field.
5. Six types of task were used, including identifying a projected word by touch, naming an object drawn unseen from a bag and matching a picture shown to the right hemisphere.

Results

1. Objects held in the right hand could be named, while objects held in the left hand could not be named but could still be retrieved by touch.
2. The right hemisphere managed simple arithmetic and was superior at spatial and block-design tasks.
3. A picture of a nude presented to the right hemisphere produced a participant who giggled or blushed but could not report seeing anything.

Conclusions

1. The left is the primary hemisphere for processing language, which is why only what reaches the left side can be spoken about.
2. The right hemisphere could read words, make mental associations, process emotional reactions and solve simple arithmetic.
3. It was also better than the left at spatial skills.
4. The right hemisphere can take in information, feel it and act on it without putting it into words, so once the corpus callosum is cut the two hemispheres can act independently.

Strengths and weaknesses

1. A strength is that the presentation was highly controlled, because a stimulus lasting one tenth of a second reached one hemisphere only.
2. A second strength is that this level of control makes the procedure repeatable by other researchers, which supports its reliability.
3. A weakness is that the sample was 11 atypical patients with long-standing epilepsy, which is a serious limit on generalisability.
4. A second weakness is that their brains had already been altered by years of seizures and by the operation, so they may not represent people with an intact corpus callosum.

Turning this into marks

1. Quote the figures, because the 11 patients, the six tasks and the one tenth of a second presentation each earn credit.
2. Name the KEY and CASE result, that patients said 'case' yet still picked out the key with the left hand.