Split-brain research into hemispheric lateralisation

Hemispheric lateralisation

is the idea that the two halves of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemishpere rather than the other.

Sperry and his colleagues decided to investigate the idea of neural processes being organised this way. 

Normally the hemispheres are connected by the corpus callosum. A commissurotomy is an operation to cut the corpus callosum and is sometimes performed to control epilepitic seizures.

Sperry studied a group of epilectics who had the operation. 

Sperry devised a unique procedure to test his split-brain patients.

In which an image is or word is projected to a patients right visual field. Which is processed by the left hemisphere.

And then another image to the left visual field processed by the right hemisphere.

In the normal brain the corpus callosum 'shares information between both hemispheres. In the split-brain the information cannot be shared from the chosen hemisphere to another. 

Object shown to the right visual field - the patient easily describes what is seen.

Objects shown to the left visual field - the patient says there is nothing there.

This is due to the fact that for most people language is processed in the left hemisphere.

In a normal brain messages from the right hemisphere are usually relayed via the corpus callosum to the language centers in the left hemisphere.  

objects projected to the left visual field - could not name them but could select a matching object using left hand 

left hand could also select an object that was asscoaited with the image presented to the left visual field. 

In each case the person could not verbally identify what they had seen but could understand what the object was. 

Two words presented on either side of the visual field e.g key presented to the left and ring to the right.

The person would write key with left hand and say the word ring. 

Composite picture made up of two different halves of a face was presented. Left hemisphere dominated the verbal description and the right hemishpere dominated the selection of a matching picture.

One strenght of split-brain research is that it shows lateralised brain functions. The left hemisphere is verbal and the right is adept at spatial tasks.  

The right hemishpere can only produce basic words and phrases but contributes emotional content to language. 

Recent research suggests this distinction may be too simplified and several tasks associated with one hemisphere can be carried out by the other.