Split Brain Research into Hemispheric Lateralisation - Sperry

Question 1

what is hemispheric lateralisation

Answer 1

the idea that the two halves of the brain are functionally different and that behaviours and mental processes are localised on one particular side → when split apart they have limited/no communication between them

Question 2

what is split brain research

Answer 2

series of studies that began in the 1960s (and are still ongoing) involving epileptic patients who had experienced surgical removal of the corpus callosum → band of fibres connecting brain hemispheres

Question 3

what is the premise of split brain research

Answer 3

• Sperry set out to study which neural processes are lateralised.
• Language is subject to hemispheric lateralisation.
• This means that it is almost entirely controlled by the left hemisphere (where Broca’s and Wernicke’s areas are located)

Question 4

what does LVF stand for and where is it processed

Answer 4

• left visual field
• processed in the right hemisphere

Question 5

what does RVF stand for and where is it processed

Answer 5

• right visual field
• processed in the left hemisphere

Question 6

what was Sperry’s split brain study

Answer 6

• The 11 ppts had previously undergone treatment to sever their corpus callosum as a way of trying to control their epilepsy.
• This procedure results in the main communication line of the two hemispheres now ceasing to exist.
• This enabled Sperry to investigate which hemispheres controlled particular actions and processes.

Question 7

what was Sperry’s procedure

Answer 7

-The procedure involved setting tasks separately to the two hemispheres.
- One of the tasks involved asking participants to respond to visual information.
- Pps were asked to fixate on a point in the middle of a screen. The researchers would then project a stimulus on either the left or right hand side of the fixation point for less than 1/10 of a second.
- The presentation time is so small to ensure that the participant does not have time for eye movement (eyes can’t converge) as this would spread the information across both sides of the visual field and therefore across both sides of the brain.
- As language is processed in the left hemisphere, when a stimulus is presented to the left visual field of a split-brain patient they could not name the stimulus.
- E.g. flashing up the word “key” to the left visual field the ppt would not be able to name the object and would respond that they had seen “nothing”. They can see it, however due to no communication between hemispheres they cannot say it.
- However, if given a variety of objects to choose from (by touch only) they would be able to select a key. They would also be able to draw a key, due to the spatial ability being on the right side of the brain.

Question 8

explain the results found

Answer 8

• The right hemisphere is basically mute. It cannot talk. (no speech centres)
• Broca’s and Wernicke’s areas are in the left hemisphere.
• Therefore the pp’s inability to name objects was due to their lack of language centre in the right hemisphere.

Question 9

what are the +ve AO3 points for split brain research

Answer 9

• credibility + validity
• advantages of lateralisation
• contribution to science
• triangulation

Question 10

expand on the +ve AO3 point for split brain research: credibility + validity

Answer 10

• The tasks were carried out in highly controlled laboratory conditions, using specialised equipment and were highly standardised. This means the validity of the experiments is high. → replicable
• e.g. the fact that the stimulus was only shown for 1/10 of a second meant that the pp couldn’t scan the visual field an increased internal validity

Question 11

expand on the +ve AO3 point for split brain research: advantages of lateralisation

Answer 11

• due to ethics, the only sample of pps used historically have been those who have undergone the split brain procedure due to medical necessity.
• However, research has been carried out with animals.
• Rogers (2004) found that chickens who had undergone the procedure had enhanced ability to perform two tasks simultaneously (searching for food whilst being vigilant of predators).
• This would be an interesting area for future research, moving away from seeing split-brain as a disability and investigating how it could advance abilities rather than hinder them.

Question 12

expand on the +ve AO3 point for split brain research: contribution to science

Answer 12

• Sperry won a Nobel Prize for his work in 1981 because of the massive contribution he made in advancing our understanding of the brain.
• This was a seminal study (altered the way we think + our understanding of the field) in neuroscience and has paved the way for further research which is still ongoing.

Question 13

expand on the +ve AO3 point for split brain research: triangulation

Answer 13

Used a mixture of quasi experiments + case studies → uses qualitative and quantitative data → increases validity

Question 14

what are the -ve AO3 points for split brain research

Answer 14

• generalisability
• unfortunate implication

Question 15

expand on the -ve AO3 point for split brain research: generalisabilty

Answer 15

• A major criticism of the procedure was Sperry’s sample - 11 patients who had undergone a very specialised surgery.
• It is argued that we cannot generalise the findings of these studies to the general population and therefore their application is limited.
• Perhaps the pps’ severe epilepsy had caused significant changes to the brain which influenced the findings. → didn’t test before so don’t know
• It is now estimated that only 80% of people have speech and language lateralised in the left hemisphere. Handedness and gender effect its location.

Question 16

expand on the -ve AO3 point for split brain research: unfortunate implication

Answer 16

• One unfortunate implication of Sperry’s work (that he had absolutely no control over!) is that it has sparked a body of pop-psychology literature which hugely over-emphasises the functional distinction between the left and right hemispheres.
• people claiming they are “left-brained” or “right-brained” has absolutely no scientific credibilty.