split brain research Flashcards
what is hemispheric lateralisation
- the idea that the two hemispheres of the brain are functionally different and certain processes are controlled by one hemisphere rather than the other eg brocas area is lateralised to the left
how are the two hemispheres connected
by the corpus callosum - a bundle of nerve fibres
the corpus callosum allows
the two hemispheres to communicate by sending information to and receiving information from each other
why is the corpus callosum needed
so we can talk about things experienced by our right hemisphere such as facial recognition
the right hemisphere
is responsible for facial recognition
the left hemisphere
is responsible for language
what are split brain patients
people with their corpus callosum severed
why were their corpus callosums severed
to prevent violent epileptic seizures from crossing one hemisphere to the other
outline sperry and gazzanigas study
- conducted a lab experiment where they compared the performance of
11 split-brain patients who had undergone surgery for their epilepsy to people with no
hemispheric de-connection and no history of epilepsy. - ptps were asked to fixate on a dot in the centre of a screen while a word or image
was presented to either the left or right visual field for less than 1/10 of a second. - without being able to see what their hands are doing, they would be asked to make
responses with their left hand, their right hand, or verbally.
results of sperry and gazzanigas study
when a picture of an object was shown to a patient’s right visual field the patient could
easily described what was seen but, if the same object was shown to the left visual field, the
patient typically reported that there was nothing there.
* they were, however, able to select a matching object from a grab-bag of different objects
using their left hand.
* If two words were presented simultaneously on either side of the visual field the patient
would write the word on the left with their left hand and say the word on the right.
* When asked to match a face from a series of other faces, the picture processed by the right
hemisphere was consistently selected and the pictured presented to the left hemisphere
was consistently ignored.
* They concluded that different hemispheres of the brain are responsible for different tasks
e.g., the left side is responsible for language
the case study of tan
supports hemispheric lateralisation
- Broca studied a patient who could only speak one word (‘tan’) but could easily
understand speech. After his death, Broca performed an autopsy on Tan’s brain and found
substantial damage to an area towards the base of the frontal lobe. Broca then investigated
more than 12 cases where patients had the same symptoms as Tan and he found that they had
damage in the same area. Broca concluded that this area was responsible for speech
production.
- This is a strength of the hemispheric lateralisation theory because it suggests that the left
hemisphere alone is responsible for speech production.
case studies arent representative
Case studies of individuals are, by their very nature, unrepresentative. This is because there is
no certainty that they are typical of the population from which they are drawn.
- Consequently, we cannot be certain that the localisation of brain function demonstrated by
‘Tan’ would be apparent in other human beings.
- These studies therefore do not prove that brain function is localised in the way the theory
suggests.
quasi experiment - high control
- strength of Sperry & Gazzaniga’s research is that it is a quasi-experiment as they were able to take advantage of a naturally occurring variable as the epileptic patients had suffered hemisphere disconnection.
- when they conducted their experiment they were able to have high control over the
experimental environment and so demonstrate the effect that hemisphere disconnection had
on brain function. - Since hemisphere disconnection (IV) was regarded as the only significant difference between the two groups studied by Sperry & Gazzaniga, the observed difference in performance (DV) was seen as having been caused by this disconnection so providing support for the theory of
hemispheric lateralisation. - Consequently, it can be argued that this study has high internal validity.
contradictory evidence about language
- limitation of the hemispheric lateralisation theory is that language may not be restricted to the left hemisphere in all people.
- For example, right-handed people generally develop their language in the left hemisphere, but left-handed people may have them on either side or both.
- This is a limitation because it may be wrong to assume that lateralisation of language centres is universal – i.e. occurs in all people
