Key study: Sperry (1968) split-brain patients

Aim: to investigate the effects of hemisphere deconnection (cutting the corpus callosum) and what this shows about the functions of each hemisphere.
Sample: 11 split-brain patients who had had their corpus callosum cut to control severe epilepsy.
Procedure: a set of standardised tests.
Visual tests: the patient stared at a central point. A word or picture was flashed to the left or right visual field for about 1/10 of a second, too fast for the eyes to move. Information in the left visual field goes to the right hemisphere, and vice versa.
Touch tests: objects were placed in the left or right hand, hidden behind a screen, and the patient had to name or find them.

Right visual field (left hemisphere): patients could name and describe the image in speech and writing.
Left visual field (right hemisphere): patients said they saw nothing, or only a flash, but could pick out the matching object with their left hand.
Key and case: with 'KEY' on the left and 'CASE' on the right, patients said 'case', but their left hand chose a key.
Objects felt with the right hand could be named; objects felt with the left hand could not be named but could be found again by touch.
Emotional pictures shown to the right hemisphere sometimes produced blushing or giggling, though the patient could not say why.
Conclusion: the hemispheres are lateralised: language is mainly in the left. When disconnected, each hemisphere seems to have its own perceptions and memories, like two separate minds.

Strengths: highly standardised procedures (fixed timings, controlled visual fields), so results can be replicated. Gave important evidence for lateralisation.
Weaknesses: a small, unusual sample (11 people) with long-term epilepsy, so their brains may not be typical; results may not generalise. The extent of surgery and the time since surgery varied between patients. In everyday life, patients can move their eyes, so the effects were less obvious outside the lab.