Split Brain Research and Hemispheric Lateralisation

Question 1

Hemispheric Lateralisation

Answer 1

• The idea that the 2 hemispheres of the brain are functionally different.
• Certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other. Language

Question 2

Split Brain studies

Answer 2

• Involve epileptic patients who received surgical separation of the brain hemispheres.
• Allows researchers to establish the extent to which brain function is lateralised.

Question 3

Split Brain procedure

Answer 3

• Projecting stimuli to each hemisphere separately.
• Intact human visual system organised so if an object is presented to RVF it is processed by left hemisphere and vice versa.
• In normal human brain, corpus callosum immediately shares info between both hemispheres creating a complete picture.
• Split brain patient focuses straight ahead - stimulus presented to RVF and only processed by left hemisphere. Brain unable to pass info to right hemisphere.

Question 4

Who were Sperry and Gazzaniga?

Answer 4

• First to investigate hemispheric lateralisation using split brain patients.

Question 5

Sperry and Gazzaniga Aim

Answer 5

• Examine the extent to which the 2 hemispheres are specialised for certain functions.

Question 6

Sperry and Gazzaniga Procedure

Answer 6

• Image/word projected to patient LVF, processed by right hemisphere or other way around.
• When info presented to one hemisphere in split brain patient, information not transferred to other hemisphere. Corpus Callosum is cut.
• Conducted many different experiments.
• Describe what you see - picture presented to either left or right VF and participant had to describe what they saw.
• Tactile test - object placed to either right or left hand, had to describe what they felt or select a similar object.
• Drawing task - p presented with picture in either RVF or LVF and had to draw what they saw.

Question 7

Sperry and Gazzaniga Findings

Answer 7

• Describe what you see - when picture present in RVF, patient could describe what they saw, demonstrating superior of left hemisphere for language production. For LVF, patient could not describe and often reported nothing present.
• Tactile tests - Object in right hand, describe verbally what they felt or identify similar object. Object in left hand, not describe and could only make wild guesses. However, could identify.
• Drawing Tasks - picture presented to RVF, while right hand attempted to draw picture it was never as clear as the left hand. Presented to LVF would consistently draw clearer even when p were right handed. Demonstrates superior of right hemisphere for visual motor tasks.

Question 8

Sperry and Gazzaniga Conclusion

Answer 8

• Highlights a number of key differences between 2 hemispheres.
• Left hemisphere is dominant in terms of speech and language.
• Right hemisphere dominant in terms of visual motor tasks.

Question 9

Evaluation of split brain research and hemispheric lateralisation - ground breaking research

Answer 9

• Sperry work changed the view of hemispheric function.
• Now a sizeable body of research on this area showing that the left hemisphere is more analytic and verbal while the left hemisphere is good at visual, spacial and musical tasks. The left is the analyser and the right is the synthesiser.
• Strength - supports view that hemispheres have different functions to each other.

Question 10

However - ground breaking research

Answer 10

• Only 10 - 15 patients have been subjected to systematic study.
• This is a very small sample, but then the procedure is very rare. They are a varied group, diff ages, handedness and gender.
• The surgical procedures they underwent were not always the same. Some had hemispheres completely separated while others had the anterior comminssure left intact.
• Weakness - despite ingeniousness of the procedure, sample is unrepresentative.

Question 11

Evaluation of split brain research and hemispheric lateralisation - Standardised procedures

Answer 11

• Sperry divided field method was ingenious and very well controlled.
• Used all sorts of ways to ensure only one hemisphere was receiving the stimuli at a time.
• Strength - information gathered is both valid and reliable.

Question 12

Furthermore - standardised procedures

Answer 12

• Sperry work promoted a philosophical debate about the mind and consciousness.
• Pucetti suggested that hemispheres are so functionally different that maybe they represent duality in the brain or two minds. Other researchers believe the the hemispheres are entwined and integrated system that are both involved in everyday tasks.
• Strength - debate in science leads to new discoveries and our understanding of the brain in enhanced.

Question 13

Evaluation of split brain research and hemispheric lateralisation - lateralisation is overstated

Answer 13

• In the mainstream literature the difference between the hemispheres has been oversimplified down to verbal and non verbal.
• Modern neuroscientists would argue the distinction is less clear cut.
• Weakness - two hemispheres are in constant communication and many behaviours can be done equally well by either hemisphere.