Hemispheric Lateralisation and Split-brain research

Question 1

What is the difference between Localisation and Lateralisation?

Answer 1

• Localisation: some functions are governed by specific areas in the brain
• Lateralisation: there are two hemispheres, for some functions localised areas appear in both areas

Question 2

How does lateralisation work in terms of language?

Answer 2

• two main centres in LH (Broca’s area in left frontal lobe, Wernicke’s in left temporal lobe)
• Language is lateralised (only performed in one hemisphere)
• RH contributes emotional context to what’s being said
• LH is analyser and RH is synthesiser

Question 3

Which functions are not lateralised and how does the motor area work in terms of lateralisation?

Answer 3

• vision, motor and somatosensory areas appear in both hemispheres
• in case of the motor area the brain is cross-wired (contralateral wiring) RH controls movement on left side of body and vice versa

Question 4

How does the visual area work in terms of lateralisation?

Answer 4

• visual area is both contralateral and ipsilateral (same-sided)
• both eyes recieve light from LVF and RVF. LVF of both eyes connects to RH and RVF of both eyes connects to LH
• allows visual area to compare the slightly different perspective from each eye and aids depth perception

Question 5

What is meant by a ‘split brain’ and who conducted the research?

Answer 5

• severing connections between RH and LH (mainly corpus callosum)
• surgical procedure to reduce epilepsy as during seizure there is excessive electrical activity travelling from one hemisphere to the other
• Sperry

Question 6

What was Sperry’s procedure?

Answer 6

• 11 pps had an image projected into their RVF (processed by LH) and same/different image projected to LVF (processed by RH)
• In normal brain corpus callosum shared image between both hemispheres, however only sharing it with one hemisphere for split brain meant info could not be shared

Question 7

What were Sperry’s findings? -

Answer 7

• when shown to RVF (LH) pps could describe what was seen but not if image shown to LVF , because in ‘normal’ RH gives info to LH to verbalise it but not possible in split brain
• Although no verbal labels, could select a matching object using left hand/ object closet to image (e.g shown cigarette pick up ashtray)
• If shown pinup picture emotional reaction (giggle) but said they couldn’t see anything

Question 8

What did Sperry conclude?

Answer 8

• show how certain functions are lateralised in brain and supports the view LH is verbal and RH is ‘silent’ but emotional

Question 9

What is one strength of Lateralisation?

Answer 9

• Fink used PET scans to identify brain area that were active during visual processing task (when pps looked at pic of whole forest engaged RH but when focus on detail e.g single tree LH)
• shows lateralisation applies in connected brains as well as split ones

Question 10

What is on weakness of Lateralisation?

Answer 10

• LH as analyser and RH as synthesiser might be wrong, people do not have a more dominant side of the brain which creates a different personality. Nielsen analysed over 100 brain scans from people aged 7-29 years no evidence of dominants side e.g artist brain or mathematician brain
• notion of left brained and right brained people is wrong

Question 11

What is one limitation of Sperry’s research?

Answer 11

• causal relationship hard to establish as compared to neurotypical control group, none had epilepsy which is a major confounding variable, differences may have been a result of epilepsy rather than split brain

Question 11

What is one strength of split-brain research?

Answer 11

• Gazzaniga showed split brain pps performed better than ‘normal’ on certain tasks e.g faster identifying the odd one out in a range of similar objects. Kingstone: normal brain LH’s better cognitive strategies are ‘watered down’ by inferior RH