split brain research Flashcards
what is hemispheric lateralisation
the idea that the two halves (hemispheres) of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other, as in the example of language
( which is both lateralised and localised)
how did Sperry study split-brain study
Sperry (1968) studied involved a unique group of individuals
these individuals underwent an operation called commissurotomy which is where the corpus callosum and other tissues which connect the two - hemispheres were cut down the middle in order to separate the two hemispheres and control frequent and severe epileptic seizures - this meant that the main communication between two hemispheres was removed
what did the severing of corpus collosum do
it removes the main communication between two hemispheres was removed
Sperry and colleagues therefore could see the extent to the two hemispheres were specialised for certain functions, and whether certain hemispheres performed tasks independently of one another
what was the procedure in Sperry’s study
Sperry devised a general procedure in which an image or word could be projected to patients RIGHT VISUAL FIELD processing the LEFT HEMISPHERE
the image could be projected to the LEFT VISUAL FIELD processing RIGHT HEMISPHERE
in the “normal” brain, the corpus callosum would immediately share the info between both hemispheres giving a complete picture of the visual word
however, presenting the image to one hemisphere of a split-brain patient meant that the info could not be conveyed from that hemisphere to other
what were the key findings from Sperry’s study
describing what you see
recognition by touch
composite words
matching faces
describing what you see
when a picture of an object was shown to a patient’s right visual field, the patient could easily describe what has seen it, however, the same object was shown to the left visual field the patient could not describe what was seen and typically reported that there was nothing there
You may recall that most people ( and this was true for all of Sperry’s patients) language is processed in the left hemisphere
Thus, the patient’s inability to describe objects in the left visual field (processed in the right hemisphere)
In the normal brain, messages from the right hemisphere would be relayed to the language centres in the left hemisphere
recognition by touch
although patients could not attach verbal labels to object projected in left visual field
were able to select matching object from a grab bay of different objects using their left - hand (limited to right hemisphere)
The object were placed behind a screen as that was most closely associated with an object presented to to the left visual field ( e.g. a ashtray selected in response to a picture of cigarette)
In each case the patient was not able to verbally identify what they had seen but could nevertheless “understand” what the object was using the right hemisphere and select the corresponding object
composite words
if two words were presented simultaneously one on either side of their visual field
the key is on the left-hand side and the ring is on the right
e.g. patient would write with their left hand the word key which is linked to the left visual field and say the word ring
matching faces
the right hemisphere also appears to be dominant in terms of recognising faces
when asked to match face from a series of other faces the picture processed by the right hemisphere (left visual field)) was consistently selected while picture presented to the left hemisphere 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 verbal description whereas the right hemisphere dominated in terms of seeking a matching picture
what functions are lateralised
language is lateralised in the left hemisphere
the right hemisphere can only produce rudimentary words and phases but contributes emotional context
this has led to the suggestion that the left hemisphere is the analyser whilst the right hemisphere is the synthesiser
what functions are not lateralised
many functions are not lateralised such as vision, motor and somatosensory areas which appear on both hemispheres
however, in the case of the motor area, the brain is cross-wired (contralateral wiring) and so the right hemisphere controls movement of the left-hand side of the body whilst the LH controls movement on the right
describe lateralisation of vision
in the case of vision, the situation is complex - it is both contralateral and ipsilateral (opposite and same sided)
Each eye receives light from the left visual field (LVF) and the right visual field (RVF)
However, the LVF is connected to the RH and the RVF is connected to the LH
This enables the visual areas to compare the slightly different perspectives from each eye and aids depth perception
There is a similar arrangement for auditory input to the auditory input to the auditory area and the disparity between the two inputs helps us locate the source of the sounds
