Hemispheric Laterisation Flashcards
Outline left & right hemispheres
Language = 2 main centres only in LH - BA & WA, thus language is lateralised: performed by 1 hemisphere rather than other
Many functions not lateralised, like vision - it’s both contralateral & ipsilateral (opposite & same-sided)
Each eye receives light from left visual field & right visual field
LVF of both eyes connected to RH & vice versa - enables visual areas to compare slightly different perspective from each eye & aids depth perception, similar arrangement for auditory input
Outline split-brain research
Sperry (1968)
11 people who’d split brain operation studied using setup in which image could be projected to LVF
In ‘normal’ brain corpus callosum would immediately share info between both hemispheres, giving complete picture of visual world
Presenting image to one hemisphere of split-brain parti meant info can’t be conveyed from that hemisphere to other
When picture of object was shown to parti’s RVF, they could describe what they’d seen, but couldn’t do this for LVF, they said nothing’s there, bc messages from RH couldn’t be relayed to language centres in LH
Although parties couldn’t give verbal labels to objects projected to LVF, they could select matching or closely linked object out of sight using left hand (linked to RH)
If pinup of picture shown to LVF there was emotional reaction but parties usually reported seeing nothing or flash of light
Conclusions: observations show how certain functions lateralised in brain & support view LH = Verbal & RH is ‘silent’ but emotional
Evaluate hemispheric lateralisation
Strength - LATERALISATION IN CONNECTED BRAIN
E.g. - Fink et al. (1996) used PET scans to identify which brain areas were active during visual processing task. When parties with connected brains attended to global elements of image regions of RH were much more active. When focusing in on finer detail specific areas of LH dominated
Ex. - At least as far as visual processing concerned, hemispheric lateralisation is feature of connected brain as well as split-brain
Limitation - ONE BRAIN
E.g. - May be different functions in RH & LH, but research suggests people don’t have dominant side if their brain which creates different personality. Nielsen et al. (2013) analysed brain scans from over 1000 people aged 7-29 & found people used certain hemisphere for certain tasks (evidence for lateralisation). But no evidence of dominant side, e.g. not artist’s brain
Ex. - Suggests notion of right- or left-brained people is wrong
Evaluate split-brain research
Strength - RESEARCH SUPPORT
E.g. - Gazzaniga (1989) showed split-brain parties perform better than connected controls on certain tasks, e.g. faster identifying odd one out in array of similar objects. In normal brain, LH’s better cognitive strategies ‘watered down’ by inferior RH
E.g. - Support Sperry’s earlier findings that ‘left brain’ & ‘right brain’ are distinct
Limitation - GENERALISATION ISSUES - Casual relationships hard to establish
E.g. - Behaviour of Sperry’s split-brain parties compared to neurotypical control group
Issue = none of parties in control group had epilepsy - major confounding variable as any differences observed between 2 groups may be result of epilepsy rather than split brain
Ex. - Some of unique features of split-brain parties’ cognitive abilities might’ve been due to their epilepsy
