Split-brain research into hemispheric lateralisation

• The two hemispheres of the brain are different in their functions. As such, it is said that the hemispheres have their own functional specialisations.
• The left and right hemispheres of the brain are connected by the corpus callosum, a bundle of nerve fibres that facilitates interhemispheric communication.
• Interhemispheric communication has been studied through cases with patients that had their corpus callosum severed. This is called a commissurotomy. The idea of this was to prevent the violent electrical activity that triggered seizures across the hemispheres.
• Sperry and Gazzaniga did 'split-brain' studies, taking advantage of the contralateral functions and communication of the two hemispheres.
• The 'describe what you see' task involved presenting visual information to individual hemispheres. This was achieved by covering one of the patient's eyes and briefly flashing an image to the exposed visual field. They were then asked to describe what they saw.
• Patients that were shown the image in their left visual field were unable to describe the image. This is because language centres such as Broca and Wernicke's area are located in the left hemisphere of the brain, so the right hemisphere alone could not produce speech.
• When the image was shown to the right visual field, the patient was able to describe the image they were shown. This is because the left hemisphere, which controls the right VF contains speech centres, allowing the patient to describe the image.
• The second test was called the 'tactile test'. Patients were asked to describe an object placed in one of their hands, then choose an appropriate similar object from a series of other objects.
• Patients using their right hand were able to both describe the object and choose a similar object. Whilst unable to describe the object when held in the left hand, patients experienced no issues with choosing a similar object, suggesting that patients were still able to understand what the object was, but not verbalise it.
• Limitation of split brain research - small sample sizes.

  -A key limitation is that the sample of participants used would have an extreme case of epilepsy, requiring the commisurotomy. As such the sample would be very limited.

  -Also such patients with severe mental issues may have had their behaviour altered as well, affecting task performance.

  -Hence it is not appropriate to generalise such results to a wider population as it is not representative.
• Strength of split brain research - lab study

  -Sperry and Gazzaniga’s research was conducted in a lab setting with highly controlled variables.

  -While doing the ‘describe what you see‘ task, each of the eyes not in use would be covered, and they would also use a fixed red dot for the ppt to focus on to ensure no interference with otheir visual fields.

  -Hence there is high internal validity as any extraneous variables were controlled.