split brain studies Flashcards
who researched into split brain studies?
Sperry
Sperry’s research background- what is commissurotomy?
when corpus callosum and other tissues which connect hemispheres are cut down middle to separate hemispheres –> means hemispheres can’t communicate and you can find exactly what each hemisphere is capable of ‘unaided’ by other –> visual pathways can’t crossover
Sperrys procedure- how many ppts and what did the ppts all have, when was it and what kind of experiment was it
- 11 participants in quasi experiment (1988) who had corpus callosum cut to treat epilepsy + reduce severe epileptic seizures
–> epilepsy= caused by a electric storm in brain= so cutting it= electrical seizure can’t bounce between hemispheres
Sperrys- procedure what did he do?
- asked ppts to stare at a fixation point at centre of screen –> images + words flashed either side of fixation point briefly= test what they’re seeing in each visual field
–> right visual field normally processed in left hemisphere (vice versa) - subject then asked to write, say or feel what they saw
Sperrys findings for right visual field
- when object displayed in right visual field and processed in left hemisphere= ppts can describe it in speech and writing
Sperrys findings for left visual field
- object displasyed in left visual field and processed in right hemisphere ppts can’t say what they have seen and instead say they saw nothing
BUT if asked to use left hand to feel for to a matching object on table= they can do this while still saying they see nothing
what were Sperrys variations
- describe what you see task
- tactile test
- drawing task
- draw and say- composite words
- matching faces
Sperrys variation- describe what you see task
- picture presented on either left or right visual field + ppt had to describe what they saw
RESULT - picture shown in right visual field and processed in left hemisphere= can verbally describe pic but can’t if shown in left visual field
Sperrys variation- tactile test
- object placed in left or right hand + they had to describe what they felt/select a similar object
RESULT - placed in right hand can identify what feel + identify object BUT left hand= they couldn’t
Sperrys variation- drawing task
- ppts presented with pic in either right or left visual field and had to draw what they could see
RESULT
when presented in left visual field could draw a pic perfectly with left hand could still draw it from right visual field with right hand but not as well
Sperrys variation- draw and say- composite words
- presented with 2 words in each visual field e.g. ‘key’ on left ‘ring’ on right
RESULT
patients would select key with left hand and say word ring
Sperrys variation- matching faces
- if a face shown to each visual field then ppt constantly selected and matched face shown to left visual field –> suggests right hemisphere is dominant in recognising faces
—> picture shown with 2 different halves of a face (one half to each hemisphere) —> left hemisphere= best at verbal description and right dominated in terms of selecting picture
sperrys conclusion
- when seperate hemispheres= can see they act differently –> act independently BUT this= overstatement
- right hemisphere can recall and identify stimuli but can’t verbalise it or write it –> BUT can show non-verbally that mental processes= centred around left visual field and left half of body are present
- left hemisphere= specialised for speech and writing
sperrys conclusions- left hemisphere
Speech- production of speech and comprehension of meaning
Auditory processing- sounds related to speech
Visual processing- fine details
sperrys conclusions- right hemisphere
Speech- emotional tone, understanding jokes and humour etc. Emotional content of speech
Auditory processing- non-language environmental sounds (rain etc)
Visual processing- bigger picture, spatial processing (arranging pieces of pic, drawing a pic etc)
eval part 1
- Sperry demonstrated lateralised brain functions
- experiment= standardised, well-controlled, replicable (he asked ppts to stare at fixed point and presented stimuli for only 1/10th of a second= ensured each hemisphere received info from only one visual field)
eval part 2
- Sperry triggered philosophical debate about nature of the mind –> 2 hemispheres are so functionally different could they be considered 2 minds?
- small sample size of 11 split brain ppts –> as some ppl have more lateralised brains than others= some had disconnection of hemispheres= individual differences influence results
eval part 3
- Sperry’s original ppts= epileptic and had unique changes in brain which could influence findings AND control group (not split brain)= non-epileptic ppts —> findings not generalisable
- sex differences–> woman said to have less lateralised brains= influences result of brain damage –> Kimura said aphasia in men who had left hemisphere damage was more than women with left hemisphere damage
eval part 4
- reductionist explanation for human behaviour as most tasks involve mix of left and right brain skills e.g. hear speech and decode words in left hemisphere and add emotional tone in voice using the right
