9. hemispheric lateralisation Flashcards
what is the basis of hemispheric lateralisation
the theory that the two halves of the brain are functionally different.
each hemisphere has functional specialisations - for example, neural mechanisms for some functions (language) are localised primarily in one half of the brain.
what did broca establish in terms of hemispheric lateralisation
damage in a particular area of the left brain hemisphere led to language deficits yet damage to the same area of the right hemisphere did not have the same consequence.
although language is primarily dominated in the left hemisphere, we could still talk about things that are experienced in the right hemisphere = two hemispheres are connected.
this allows information received by one hemisphere to be sent to the other hemisphere through connecting bundles of nerve fibres such as the corpus callosum.
what was the aim of sperry and gazzangia research
to test the capabilities of the separated hemispheres.
they were able to send visual information to just one hemisphere at a time in order to study hemispheric lateralisation - so because the corpus callosum is cut in split brain patients the information presented to one hemisphere has no way of travelling to the other hemisphere and can be processed only in the hemisphere that received it.
what was the procedure of sperry and gazzangia research
split brain patients undertook a surgical procedure where the corpus callosum is cut - commonly done as a treatment for severe epilepsy.
the split brain patient would fixate on a dot in the centre of a screen while information was presented to either the left or right visual field. they would then be asked to make responses with either their left hand (controlled by the right hemisphere) or their right hand (controlled by the left hemisphere) or verbally (which is controlled by the left hemisphere).
what were the findings of sperry and gazzangia research
describe what you see - in the left hemisphere the patients described what they saw but in the right hemisphere they could not = superiority of left hemisphere for language production.
drawing - in the left hemisphere the participant consistently drew better and clear pictures than the right = superiority of right hemisphere for visual tasks.
what were the conclusions of sperry and gazzangia research
left hemisphere = dominant in terms of speech and language.
right hemisphere = dominant in terms of visual motor tasks.
strength - increases neural capacity
rogers found that in a domestic chicken brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators).
using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions.
= provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks.
weakness - language is not restricted to the left hemisphere
turk (2002) discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, eventually leading to the ability to speak about the information presented to either side of the brain.
= perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.
weakness - flawed research
sperry research is flawed because split brain procedure is rarely carried out now meaning patients are hard to come by.
such studies often include very few participants and often research takes an idiographic approach. therefore any conclusions drawn are representative only of those individuals who had confounding physical disorder that made the procedure necessary = lacks population validity.
strength - highly standardised procedures
participants stared at a fixed point and images were shown for 1/10th of a second so the eye would not have time to move over the image and spread information across both visual fields and subsequently both sides of the brain - ensures only one hemisphere received information at any one time.
= standardised procedure meant that it was very well controlled so it has high internal validity. the research was specific to lateralisation so the high validity means there is less chance of confounding variables.
