Hemispheric Lateralisation & split-brain research Flashcards
What is hemispheric lateralisation?
The idea that the two halves of the brain are functionally different
How is the brain lateralised?
LH= language restricted here (Broca & Wernicke’s area)
RH- visual motor tasks e.g. spatial reasoning
better at analysing
How is the motor area contralaterally (opposite) wired?
The RH controls movement on the left side of the body
The LH controls movement on the right side of the body
How is the visual area both contralateral and ipsilateral?
- Each eye receives light from LVF & RVF
- LVF of both eyes connected to right hemisphere
- RVF of both eyes connected to left hemispheres
- What is a ‘split brain’ operation?
- involves severing the connections between the two hemispheres (corpus callosom)
- procedure used to reduce epilepsy
What does split-brain research study?
How the hemispheres function when they can’t communicate with each other
Outline Sperry’s research
- 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
What were the findings of Sperry’s research?
- 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 not give verbal labels to objects presented in the LVF but could select an object out of sight with left hand (linked to RH)
What does Sperry’s research show about hemispheric lateralisation?
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)
What research support is there for lateralisation in the connected brain?
- 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
What is a limitation of HL?
- 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.
What research support is there for recent split brain research?
- Gazzaniga showed that split-brain p’s actually perform better than connected controls on certain tasks.
- e.g. they were faster at identifying the odd one out in an array of similar objects than normal controls.
- supports Sperry’s findings that the ‘left brain’ and ‘right brain’ are distinct.
What is a limitation of Sperry’s research?
- 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
