Sperry and Split Brain Research ***

Sperry 2005

Repeated the divided field study with split brain patients, but used faces as the stimuli.

Other than Sperry, what really changed the view on lateralisation of function across the hemispheres?

Studies using non verbal stimuli.

** Gazzaniga 1998

Suggested that some of the early discoveries from split brain research have been disconfirmed by recent discoveries. e.g. split brain research suggested that the right hemisphere was unable to handle the most rudimentary language, but with JW he developed the capacity to speak out of the right hemisphere, with the result that JW can speak about information presented to either hemisphere.

What has split brain research not shown?

That the brain is organized into discrete regions with specific sections responsible for specific tasks, instead it suggests that the connectivity between the different regions is as important as the operation of the different parts.

What is Sperry's study known as?

The divided field study.

What happens as a result of cutting the corpus callosum?

The information presented in one hemisphere has no way of travelling to the other hemisphere and can only be processed in the hemisphere that received it.

What is a major limitation to the procedure?

The natural tendency for the participant to move their eyes towards the stimulus. If the eyes move too much the stimulus is likely to be picked up by both hemispheres. To prevent this, the stimulus could only be presented for a very brief period of time, around 200 milliseconds. So Sperry could only present single words or pictures.

Turk method

The patient was a 48 year old man who had commissurotomy for epilepsy 23 years previous. The stimuli were morphed faces. A series of morph faces from 0% of the patient to 100%. On one trial he pressed the button if the image was him, on another if it was the researcher.

Turk conclusion

The right hemisphere is better at processing faces but the left hemisphere may have an important role in self recognition, such as personal memories and beliefs.

Turk findings

The right hemisphere showed clear bias towards identifying the morphed face as a familiar one and the left hemisphere showed a clear bias towards identifying the morphed face as himself.

What happens in a typical split brain study?

The split brain patient would fixate on a dot in the centre of a screen while information was presented to either the left or right visual field. They would then be asked to make responses with either their left hand, controlled by the right hemisphere, or the right hand, controlled by the left hemisphere, or verbally, controlled by the left hemisphere.

** Issue with making conclusions from split brain studies?

There are very few patients, and only 10-15 have been extensively studied.

Sperry 2005 Findings

They would choose the one presented to the right hemisphere. The right hemisphere is better at facial recognition than the left.

What did split brain studies affect the way that we view the hemispheres?

Verbal left hemisphere and a visuospatial right hemisphere.

Corpus Collosum

A bundle of 200-300 million fibres.

Sperry 2005 Method

A different face was presented to each hemisphere at the same time. The patient was given a set of faces including ones presented and asked to choose the one they had seen earlier.

What is the function of the corpus callosum?

Allows epileptic discharges to travel from one hemisphere to the other, so epilepsy can control the whole brain.

Split Brain

An operation used in some cases of severe epilepsy, the technical term is commissurotomy.

What happened in the 1940s?

An operation was devised to cut the corpus callosum, so preventing the epileptic discharges involving both hemispheres and so reducing the severity of the attack.

** Why, in some split brain studies, were operations not always comparable?

As well as the corpus callous being cut, there are smaller pathways connecting the two hemispheres, and in some cases these were cut as well.

How are the two hemispheres of the brain connected?

By the corpus callosum.

What is the name of the operation conducted in the 1940s regarding split brain patients?

Commissurotomy.

What have we learnt from split brain patients?

Discovered a number of differences between the two hemispheres, such as that the left hemisphere is responsible for speech and language, and the right specializes in visual spatial processing and facial recognition.

* How varied are the group studied in split brain studies?

Extremely varied - they differ in age, gender, handedness, the age epilepsy developed, age at commissurotomy, and the age they were tested.

Sperry 1967

First to study the capabilities of split brain patients. To test the capabilities of the separated hemispheres, they were able to send visual information to just one hemisphere at a time in order to study what is known as hemispheric lateralization.

Give an example of Sperry's split brain patient study using cats and dogs?

If the patient was flashed a picture of a dog to the right visual field and asked what they had seen, they would answer dog. However, if a picture of a cat was flashed to the left visual field the patient would say they could see nothing because the information from the left is processed by the right, which can see the picture but has no verbal centre.

Sperry took advantage of the fact that...

Information from the left visual field goes to the right hemisphere and information from the right visual field goes to the left hemisphere.

Other than facial recognition, what did Sperry also show about the right hemisphere in his 2005 study?

It is better at matching shapes and doing visuospatial tasks.

How was Sperry's study impressive?

It showed that the right hemisphere had some basic language ability, however, it still reinforced the idea that language was lateralised to the left hemisphere.

What was the effects of commissurotomy?

It was not successful at reducing the symptoms of epilepsy, but the patients did not suffer ill effects.

Turk et al 2002

Looked at face processing after split brain surgery. e..g if the patient's own face was processed in a different way to the familiar face of someone else.