Hemispheric Lateralisation & Split Brain Research

Question 1

Hemispheric lateralisation - left and right hemispheres (language + motor)

Answer 1

For language:
- the 2 main centres are only in the LH - bronchas in left frontal lobe and wernikes in left temporal lobe
- so language is lateralised - one hemisphere controls it

The motor area is cross wired:
- the RH controls the movement on the left side of the body
- LH controls movements on the right

Question 2

How do the hemispheres control vision

Answer 2

• both contralateral and ipsilateral
• each eye receives light from the left visual field and the right visual field
• the LVF of both eyes is connected to the RH - the RVF of both eyes is connected to the LH
• enables visual areas to compare the different perspective from each eye and aids in depth perception

Question 3

Split brain research - why do we do them

Answer 3

• severing connections between the RH and the LH, mainly the corpus callosum
• used to reduce epilepsy
• during an epileptic seizure the brain has excessive electrical activity, travels from one hemisphere to the other
• to reduce fits the connection is cut, splits brain into 2 halves

Question 4

Sperry’s research - procedure

Answer 4

• 11 people who had split brain operation were studied
• image projected to a pts RVF and the same, or different image could be projected by the LVF
• in the normal brain, the corpus callosum, immediately share the info between both hemispheres giving complete picture
• presenting image to 1 hemisphere of split Brian pts = the info cannot be conveyed from that hemisphere to the other

Question 5

Findings

Answer 5

• when the picture was down to the pts RVF they could describe what was seen
• couldn’t do this if object was shown to the LVF, said ‘nothing was there’
  … because the split brain means messages cant be relayed from the RH to the language centres in the LH
• couldn’t give verbal labels to objects in LVF, could select a matching object that was most closely associated with an object in the LVF

Question 6

Conclusions

Answer 6

Show how certain functions are lateralised in the brain and support the view that the LH is verbal and the RH is silent but emotional

Question 7

Evaluation of hemispheric lateralisation - strength

Answer 7

Research showing that even in connected brains the two hemispheres process information differently
- fink - PET scans:
- identify which areas were active during a visual task
- pts with connected brains asked to attend to global elements image regions of the RH were more active
- when required to focus on finer detail the specific areas of the LH tended to dominate
Suggests that hemispheric lateralisation is a feature of the connected brain as well as the split brain

Question 8

Limitation of hemispheric lateralisation

Answer 8

One brain:
LH as an analyser and RH as a synthesiser may be wrong
- there may be different functions in the RH and LH but research suggests don’t have dominant side of the brain that creates a different personality.
- neilson et al - analysed brain scans - found that people used certain hemispheres for certain tasks but no evidence for dominant side

Question 9

Evaluate split brain research - strength

Answer 9

Support from more recent split brain research:
- yo mamma said et al - split brain pts perform better than control; faster at identifying the odd one out in group of similar objects than normal controls.
Supports Sperry’s earlier findings that the left brain and right brain are distinct

Question 10

Limitation of split brain research

Answer 10

Casual relationships are hard to establish:
- the beh of Sperrys split brain pts was compared to control group.
- an issue was that the pts in control group had epilepsy - confounding variable
- any differences that were observed may be due to epilepsy rather than the split brain