Lateralisation and Split-brain research

Question 1

What is Hemespheric lateralisation?

Answer 1

The idea that the two hemispheres of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other.

Question 2

What is split-brain research?

Answer 2

A split-brain operation is severing the connection between the 2 hemispheres by cutting the corpus collosum (bundle of nerve fibres connecting hemispheres). This corpus collostumy reduces epileptic symptoms and has few side effects for such an invasive procedure.

Question 3

Outline Sperrys (1968) procedure.

Answer 3

-Eleven split-brain individuals were studied using equipment that would project information to each visual field, E.g and image being presented in the RVF and processed by the LH.
-Sperry controlled the information that each hemisphere had access to.
- In a normal brain the CC would share the information between both hemispheres.
- But presenting information to one hemisphere in a SB patient meant the information could not be shared to the other hemisphere.

Question 4

Outline Sperrys (1968) findings.

Answer 4

When a picture of an object was shown to the patients RVF, the participant could describe what was seen. But they could not do this if it was shown to the LVF.
-This is because in a non-split brain the messaged from the RH are relayed to language centres in the LH, but this cant be done with split brain as there is a lack of language centres in the RH.
- Also the RH could use the left hand to select an object which was associated with what they saw in the LVF.
- This suggests certain functions of the brain are lateralised, and support the view that the LH is the language centre of the brain.

Question 5

Outline Gazzanigas (1983) research.

Answer 5

• When asked to match a face from a series of other faces the picture processed by the RH (LVF) was consistenly selected, whereas it was consistenly ignored in the LH (RVF).
• found that when each hemisphere of split-brain patients were presented with faces, the RH was much more able to recognise them. Suggesting that the RH is specialised for facial recognition.

Question 6

AO3

Strength 1: Gazzaniga Research support

Answer 6

• Gazzaniga showed that split brain participants performed better than normal controls on certain tasks.
• For example they were faster than controls in finding the odd one out in an array of similar objects.
• In the normal brain the LHs better cognitive strategies are watered down by the inferior RH (Kingston 1995).
• This supports Sperrys earlier findings that the left brain and right brain are distinct.

Question 7

A03

Limitation 1 : Casual relationships are hard to establish.

Answer 7

• The behaviour of sperrys split-brain participants was compared to a neurotypical control group.
• An issue is that none of the participants in the control group had epilepsy.
• This is a major confounding variable as any differences that were observed between the two groups may be the result of epilepsy rather than the split brian.
• Meaning some of the unqiue features of the split-brain patients cognitive abilities may have been due to epilepsy.

Question 8

AO3 - Lateralisation

Strength 1 : Lateralisation in the normal brain.

Answer 8

• Rsearch shows that even in the normal brain the two hemispheres process information differently.
• Fink (1996) used PET scans to identify which areas were active during a visual processing task. When normal participants were asked to attend to global parts of the image (looking at a whole forest) regions of the RH were much more active.
• When required to look at the finer detials (such as individual trees) specific areas of the LH tended to dominate.
• This suggests that as far as visual processing is concerned , HL is a feature of the normal brain as well as the split-brain.

Question 9

AO3-Lateralisation

Limitation 2 :Idea of LH as analyser and RH and synthesiser is wrong.

Answer 9

• There may be different functions in the RH and LH , but research suggests that there is not a dominant side of the brain which creates a different personality.
• Nielsen (2013) analysed brain scans of 1000 people aged 7-29 years old and did find that certain hempispheres where used for certain tasks.
• However there was no evidence for a dominant hemisphere suggesting that the notion of Left/right brained people is wrong.