Hemispheric lateralisation & split brain Flashcards
What is hemispheric lateralisation?
Idea that two halves of the brain (hemispheres) are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other. An example of this would be language which is localised and lateralised.
What is split-brain research?
A series of studies which began in the 1960s and are still ongoing, involving epileptic patients who had experienced a surgical separation of the hemispheres of the brain. This allowed researchers to investigate the extent to which brain function is lateralised.
What did Sperry do?
An image/word is projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere). When information is presented to one hemisphere in a split-brain patient, the information is not transferred to the other hemisphere (as the corpus callosum is cut).
Sperry and Gazzaniga conducted many different experiments, including describe what you see tasks, tactile tests, and drawing tasks.
In the describe what you see task, a picture was presented to either the left or right visual field and the participant had to simply describe what they saw.
In the tactile test, an object was placed in the patient’s left or right hand and they had to either describe what they felt, or select a similar object from a series of alternate objects.
Finally, in the drawing task, participants were presented with a picture in either their left or right visual field, and they had to simply draw what they saw.
What are the strengths of hemispheric lateralisation and split-brain research?
What did Sperry find?
When a picture was shown to a patients right visual field they could easily describe what was seen. If the same was shown to the left visual field, they couldn’t describe what was seen, often reporting that there was nothing there. For most people incl Sperry’s patients, language is processed in the left hemisphere. Therefore, patients’ inability to describe objects in the left visual field which is processed in the right hemisphere is due to lack of language centres in right. In normal brains, messages from right hem would be relayed to language centres in left hem.
Patients couldn’t attach verbal labels to objects in the visual field, they were able to select a matching item from a grab-bag using their left hand (linked to right hem). There was a wall up so patients couldn’t see the bag. Left hand was also able to select object closely matched to an object represented to in the LVF for example ashtray be selected in response to a picture of a cigarette. They weren’t able to verbally identify what they had seen but could ‘understand’ what the object was, using the RH and select the right object.
If two words were presented at the same time, one on either side of the visual field, for example ring on the right and key on the left. They found that the patient would select the key with their left hand. (left visual field goes to right hemisphere linked to left hand) and say the word ring.
Right hemisphere also appeared dominant in recognising faces. When asked to match a face from a series of other faces, the picture processed by the right hemisphere (left visual field) was consistently selected, whilst the picture presented to the left hemisphere (right visual field) was consistently ignored. When a composite picture of two different halves of a face was presented; one half to each hemisphere, the left hemisphere dominated in terms of verbal description (language centre lateralisation) whereas right hemisphere dominated in terms of selecting a matching picture.
What are the limitations of hemispheric lateralisation and split-brain research?
