Split-brain research into hemispheric lateralisation

Question 1

Gazzaniga’s(1970) research - impact on split brain monkey

Answer 1

Two independent working brains that could not communicate and had separate memory from each other

Question 2

Sperry’s 1968 split-brain research participants and aims

Answer 2

11 individuals who had undergone a commissurotomy(corpus callosum and surrounding tissue had been removed, in order to separate the hemispheres) due to experiencing severe epileptic seizures.
Due to the communication line being broken, Sherry was able to see the extent to which the hemispheres worked independently from each other.

Question 3

Lateralisation of cortical function

Answer 3

Certain areas of the brain responsible for different functions

Question 4

Procedure - split brain research: Sperry(1968)

Answer 4

1. Participants were asked to perform a range of tasks, and their performance was compared with participants with no inter hemispheric disconnection.

Question 5

Demonstrated lateralised brain functions - split-brain research

Answer 5

The pioneering work into the split-brain phenomenon has produced an impressive and sizeable body of research findings, the main conclusions of which appears to be that the left hemisphere is more geared towards analytic and verbal tasks, while the right is more adept at performing spatial tasks and music. The right hemisphere can only produce rudimentary words and phrases, but contributes emotional and holistic content to language.

Left hemisphere = analyser - analytic and verbal tasks(language)
Right hemisphere = synthesiser - emotional - spatial tasks and music

Question 6

Strengths of the methodology

Answer 6

Experiments used highly specialised and standardised procedures: The method used was ingenious - typically participants would be asked to stare at a given point(the fixation points, while one eye is blindfolded. The image projected would be flashed up for 1/10 of a second, meaning the split-brain patient would not have time to move their eye across the image and so spread the information across both sides of the visual field and both sides of the brain. Sperry was able to develop a useful and well-controlled procedures based off the original research.

Question 7

Theoretical basis - negative evaluation

Answer 7

Puncetti(1977) has suggested the two hemispheres are so functionally different that they represent a form of duality in the brain - that in effect we are all two minds and this is a situation only emphasised rather than created in the split-brain patient. In contrast, other researchers have argued that, far from working in isolation, the two hemispheres form a highly integrated system and are both involved in most everyday tasks

Question 8

Issues with generalisation - negative evaluation

Answer 8

The sample of participants is unusual: there were only 11 who took part in all variations of the basic procedure, all of whom had a history of epileptic seizures. It has been argued this may have caused unique changes in the brain that may have influenced the findings. Some of the participants had experienced more disconnection of the two hemispheres as part of their surgical procedures than others. The control group that Sperry used, was made up of 11 people with no history of epilepsy, may have been inappropriate

Question 9

Differences in function may be overstated

Answer 9

One legacy of Sperry’s work is a growing body of pop-psychological literature that overemphasises and oversimplifies the functional distinction between the left and right hemisphere. Although the verbal and non-verbal labels can, on occasion, be usefully applied to summarise the differences between two hemispheres, modern neuroscientists would contend actual distinction is less clear-cut and much messier than this. In the normal brain, the two hemispheres are in constant communication when performing everyday tasks, and many of the behaviours typically associated with one hemisphere can be effectively performed by the other when the situation requires it.

Question 10

Key findings of split-brain studies(describe what you see condition)

Answer 10

When a picture of an object was shown to a patient’s right visual field, the patient could easily describe what was seen. However, the same object was shown to the left visual field: the patient could not describe what was seen and reported nothing was there, due to the lack of language centres in the right hemisphere, as language is processed in the left. In normal brains, the right hemisphere would be replayed to the language centres in the left hemisphere.

Question 11

Key findings split-brain studies(recognition by touch)

Answer 11

Although patients could not attach verbal labels to objects projected in the left visual field, they were able to select a matching object from a grab-bag of different objects using their left hand. The objects were placed behind a screen so as not to be seen. The left hand was able to select an object that was most closely associated with an object presented to the left visual field. In each case, the patient was not able to verbally identify what they had seen but could understand what the object was using the right hemisphere and select the corresponding object accordingly.

Question 12

Key findings split-brain research studies(composite words)

Answer 12

If two words were presented simultaneously, one on either side of the visual field. The patient would write the word on the left with their left hand, and say the word on the right.

Question 13

Matching faces condition split-brain research findings studies

Answer 13

The right hemisphere also appeared dominant in terms of recognising faces. When asked to match a face from a series of other faces, the picture processed by the right hemisphere(left visual field) was consistently selected, while the picture presented to the left hemisphere was constantly ignored. When a composite picture made up of two different halves of a face was presented one-half to each hemisphere: the left hemisphere dominated in terms of verbal description whereas the right hemisphere dominated in terms of selecting a matching picture.

Question 14

What are the hemispheres joined by?

Answer 14

The corpus callosum

Question 15

Individual differences in lateralisation of function

Answer 15

Varies depending on age - language more lateralised to the left hemisphere with increasing age in children and adolescents, but after the age of 25, lateralisation decreased as people got older

Question 16

Contradicting evidence to hemispheric lateralisation

Answer 16

A patient with damage to the left hemisphere developed the capacity to speak in the right hemisphere