Split brain research Flashcards
what is the corpus callosum
a broad bundle of 55 million connecting nerve fibres that joins the two hemispheres of the brain, allowing information received by one hemisphere to be sent to the other.
How do they treat epilepsy
To treat severe epilepsy (in the past), surgeons cut the corpus callosum so that the epilepsy and accompanying electrical storms are contained within one hemisphere of the brain.
This reduces the number of epileptic fits as the hemispheres rebounding off each other can prompt seizures.
Sperry and Gazzaniga studied split-brain patients to test the capabilities of the separated hemispheres.
In a typical study:
Experimental situation/set-up: Patients fixated on a dot/cross in the centre of a screen (creating a split visual field).
Stimulus material: Information (e.g. faces, words, digits) is presented for less than 1/10 of a second (insufficient time to move eyes around) to the left and/or right visual field (i.e. to the left and/or right of the dot/cross).
Task: Patients were asked to make responses with either their left hand (controlled by the right hemisphere) or their right hand (controlled by the left hemisphere) e.g. draw what they saw or select an object from behind a screen (without being able to see what their hands are doing), or verbally (which is controlled by the left hemisphere).
Split-Brain Research Sperry & Gazzaniga (1967): Key findings
Left hemisphere (Right visual field)
1) Patients could say any words flashed to the right visual field (the right side of the screen), demonstrating the left hemisphere’s ability to produce speech (presence of Broca’s area).
2)Patients identified a painting of a face made up of fruit as ‘FRUITS’, instead of ‘FACE’ – demonstrating the left hemisphere’s ability to process detail.
3)When patients felt a plastic number with their right hand, they were able to say the number they were holding. This is due to the presence of Broca’s area in the left hemisphere.
4)When patients were asked to solve a puzzle with their right hand, they struggled, with the left hand often trying to intervene to help.
What do Sperry and Gazzaniga’s findings suggest about hemispheric lateralisation?
Do their findings support or challenge hemispheric lateralisation i.e. the idea that the left and right hemispheres have functional specialisations?
YES, split brain research supports hemispheric lateralisation.
Split-Brain Research Sperry & Gazzaniga (1967): Key findings
Right hemisphere (Left hand)
1)Patients could not say words flashed up on the left side of the screen – “I saw nothing” (no Broca’s area), but they could draw it with their left hand, demonstrating some processing of the word
2)Patients identified a painting of a face made up of fruits as a ‘FACE’ – demonstrating the right hemisphere’s ability to recognise and process faces, as well as holistic processing.
3)When patients felt a plastic number with their left hand, they could correctly signal with fingers on the same hand the number they had felt, but they could not say it out loud – the left hemisphere guessed.
4)When patients were asked to solve a puzzle with their left hand, they did so quickly, demonstrating the right hemisphere’s ability to recognise patterns and complete spatial tasks.
Summarise what their research suggests about the specific functions of the left and right hemispheres
Sperry and Gazzaniga’s research highlights a number of key differences between the two hemispheres…..
the left hemisphere is dominant for speech, language and processing detail;
the right hemisphere is dominant for facial recognition, holistic processing, spatial awareness and visual motor skills.
It is problematic to assume that split-brain research is not methodologically flawed.
The extent to which split brains were indicative of normal functioning prior to surgery is an issue, especially as the split-brain surgery was to treat a problem within the brain.
It is also possible that there were other effects on the brain of the split-brain surgery, or that the hemispheres were not entirely disconnected from one another.
Some patients experienced drug therapy for longer than others beforehand – drugs may have altered the functions within each hemisphere.
The split brain procedure is rarely carried out nowadays and patients who have had this procedure are not encountered in sufficient numbers to be useful for research purposes. Andrewes (2001) - many studies involved as few as 3 participants or just a single participant, which then makes it difficult to generalise the findings to others.
This therefore limits the extent to which the findings can be generalised to normal brains and suggests that we should be cautious when interpreting the findings of split-brain research and drawing conclusions about hemispheric lateralisation.
The data of Sperry and Gazzaniga’s research were artificially produced.
Because in real life a severed corpus callosum can be compensated for by the unrestricted use of two eyes (patients can move their eyes and head around to ensure both visual fields, and thus both hemispheres, process the information), to enable both hemispheres to process visual stimuli, rather than patients fixating on a point and different information being presented to each visual field.
This therefore makes it difficult to generalise the findings of Sperry and Gazzaniga’s research beyond the experimental setting to explain the capabilities of split-brain patients in everyday life.
(That said, their research has provided a useful insight into the functions of the two hemispheres, thus developing a clearer understanding of hemispheric lateralisation)
