Split-brain Research into Lateralisation Flashcards
what is lateralisation?
certain activities are controlled or dominated by one hemisphere rather than the other
generally the right hemisphere controlled the left side of the body, and the left hemisphere controls the right side of the body (contralateral)
what is hemispheric lateralisation?
different functions are controlled by one of the two hemispheres
ability to produce language is controlled by the left hemisphere
what was Sperry (1968)’s research?
split brain research
studied people who had undergone a commissurotomy / corpus callosotomy, where the corpus callosum and other tissues are cut to separate the hemispheres and control frequent and severe epileptic seizures, so communication between the two hemispheres was removed
what procedure did Sperry use?
a word/image could be projected to a patients right visual field (processed by the left hemisphere) or the left visual field (processed by the right hemisphere)
how many patients did Sperry study?
11, compared to a control group of ‘normal’ brains
what did Gazzaniga do?
later studied split brain patients using Sperry’s methodology
what did Ronald Pucetti (1977) suggest?
the two hemispheres of the brain are so functionally different they represent a form of duality in the brain
what did Sperry find when projecting images to the left/right visual fields of split brain patients?
when a picture of an object was shown to the right visual field, they could easily describe what they had seen
if shown to the left visual field, they could not describe what they saw and typically reported there was nothing there
this is due to the lack of language centres in the right hemisphere
what is the process of recognition by touch?
although patients could not verbalise objects projected to the left visual field, they could select a matching object from behind a screen from a grab-bag of different objects using their left hand (linked to right hemisphere)
could pick an item most closely related to what they had seen
what is the process of composite words?
two words are presented simultaneously, one to either side of the visual field
e.g. a key to the left and a ring to the right, they could write ‘key’ with their left hand and say the word ‘ring’, but not associate them together as a ‘keyring’
can you explain drawing abilities in terms of split brain research?
the right hemisphere controls drawing ability
a picture is flashed to either the left or right visual field, and the left hand continually outperforms the right hand despite all patients having a dominant right hand
which hemisphere is dominant in face recognition?
right hemisphere
what is the process of matching faces?
when asked to match a face from a series of other faces, the picture processes by the right hemisphere (shown to left visual field) was consistently selected, whereas the p other processed by the left hemisphere (shown to right visual field) was consistently ignored
when a composite picture made up of two different halves of a face was presented, one half to each hemisphere, the left hemisphere dominated in terms of visual description whereas the right hemisphere dominated in terms of matching a picture
what are the strengths of Sperry’s research?
demonstrated lateralised brain functions - concluded the left hemisphere controls analytical and verbal tasks and the right hemisphere spatial tasks and music
used a highly specialised and standardised procedure
what are the weaknesses of Sperry’s research?
theoretical - his work prompted a theoretical and philosophical debate about the degree of communication between the hemispheres - Pucetti (1977) suggested a form of duality
issues with generalisation - all 11 participants had a epileptic seizure history but some experienced more disconnection than others
differences in function may have been overstated - modern neuroscientists would argue distinction between the functions of the hemispheres are not so clear-cut and much messier
