Hemispheric Lateralisation & split-brain research

Question 1

What is hemispheric lateralisation?

Answer 1

The idea that the two halves of the brain are functionally different and that certain mental processes and behaviour are controlled by one hemisphere

Question 2

How is the brain lateralised?

Answer 2

LH= language restricted here (Broca & Wernicke’s area)> led to the view that it is the analyser
RH- visual motor tasks e.g. spatial and emotional reasoning > led to vie wthat it is the synthesisier

Question 3

How is the motor area contralaterally (opposite) wired?

Answer 3

The RH controls movement on the left side of the body
The LH controls movement on the right side of the body

Question 4

How is the visual area both contralateral and ipsilateral?

Answer 4

• Each eye receives light from LVF & RVF
• LVF of both eyes connected (proccessed) to right hemisphere
• RVF of both eyes connected (processed) to left hemispheres > this is contraleteral
• infromation from one VF also sends some signals to the same side of the brain e.g. LVF to LH > this is ispilateral
• helps brain compare both eyes input and improves depth perception
• same for sounds > locate where sound is coming from, understand speech better

Question 5

• What is a ‘split brain’ operation?

Answer 5

• involves severing the connections between the two hemispheres (corpus callosom)
• procedure used to reduce epilepsy

Question 6

What does split-brain research study?

Answer 6

How the hemispheres function when they can’t communicate with each other

Question 7

Outline Sperry’s research

Answer 7

• devised a system to study how two separated hemispheres deal with speech & vision
  different tasks:
• describe what you see- picture presented to left/right visual field & p’s asked to describe what they saw
• tactile test- object placed in p’s left/right hand, asked describe what they felt/select object
• drawing task- picture presented to left/right visual field, p’s asked to draw what they saw

Question 8

What were the findings of Sperry’s research?

Answer 8

• when picture presented to RVF (linked to LH), p’s could describe what they saw, could not when object was presented to LVF
• participants could draw image with left hand as the task does not require language

Question 9

What does Sperry’s research show about hemispheric lateralisation?

Answer 9

LH= dominant for speech and language
RH= dominant for visual motor tasks

• split brain patients less capable of completing tasks well, when made to do something with the opposite hemisphere (not responsible for said function)

Question 10

What research support is there for lateralisation in the connected brain?

Answer 10

• research shows even in connected brains, two hemispheres process information differently
• Fink et al used PET scans to identify which brain areas were active during a visual processing task.
• When p’s with connected brains were asked to attend to global elements of an image =regions of the RH were much more active.
• When required to focus on the finer detail, specific areas of the LH tended to dominate.
• hemispheric lateralisation is a feature of both connected & split- brains

Question 11

What is a limitation of HL?

Answer 11

• idea that the LH as analyser and RH as synthesiser may be wrong
• may be different functions in the RH and LH but> Nielsen et al analysed brain scans from over 1000 people & found no evidence of a dominant side that creates a different personality.
• suggests the notion of right- or left-brained people is wrong.

Question 12

what is another limitation of HL/split brain?

Answer 12

• language may not be restricted to the LH
• Turk et al discovered a patient (J.W) that suffered damage to the LH but developed the capacity to speak in the RH & eventually leading to ability to speak about the information presented to either side of the brain
• laterilisation is not fixed and the brain can adapt

Question 13

What is a limitation of Sperry’s research?

Answer 13

• causal relationships are hard to establish
• the behaviour of Sperry’s split-brain p’s was compared to a neurotypical control group
• none of the p’s in the control group had epilepsy (major CV)
• means any differences observed between two groups may be result of the epilepsy than the split brain.
• Thus some of the unique features of split-brain p’s cognitive abilities might be due to their epilepsy- reduced validity