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Sperry (1968) Split brain study
‘Hemisphere deconnection and unity in conscious awareness’
American Psychologist 23 pp723-33
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Sperry (1968) Split brain study
introduction
• brain has 2 hemispheres
• connected by commissural fibres
• lateralisation of function – each has different functions – cognitive / motor
• split to treat extreme epilepsy
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Sperry (1968) Split brain study
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Sperry (1968) Split brain study
the studies: subjects
• 11 'most radical disconnection'
• 2 benefited; others 'recent'
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Sperry (1968) Split brain study
designs: natural experiments
• variables occur 'naturally
• e.g. socio-economic- but in this case surgical procedures
• carefully controlled tests
• also case studies
• open ended interviews etc
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Sperry (1968) Split brain study
procedure • one hand feeling unseen objects • attention to one ‘visual field’ • image shown for 1/10th sec (to prevent eyes
moving to prevent use of other visual field)• 2 images shown for 1/10th s; one to each field• etc
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Sperry (1968) Split brain study
results: visual test 1
• subject show image in one visual field
• recognised if in that field before
• not recognised if re-shown in other field
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Right visual fieldLeft visual field
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Sperry (1968) Split brain study
results: visual test 2
• RH subjects shown objects in each field
• could describe object in R field
• said no object in L field, or ‘just a flash'
• able to respond non-verbally (pick up object with L hand) to object in L field
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Sperry (1968) Split brain study
results: visual / drawing test
• 2 objects shown 1in LVF, 1RVF
• drew object with shielded L hand
• reported they had drawn object in R field!
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When asked to say what they
had drawn they would name the object shown to their RVF (e.g.
banana)!
they could draw, with the left
hand, the object (e.g. pen) that
had been presented to their
LVF.
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Sperry (1968) Split brain study
results: tactile test
• objects in R hand => verbal description
• object in L hand => only NV response
• L hand unable to respond to stimulus in R hand
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When they felt and object with the right hand patients could
name the object
When they felt and object with
the left hand patients could
not name object(but could
identify it non-verbally, by picking it out from a group)
Patients would feel one object with each hand
Left hand could not respond to what the right
hand felt
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Sperry (1968) Split brain study
results: 'competing tasks'
• R and L hand had different tasks
• could do both at same time
• non-split brain subjects slowed by this
• only useful for odd lab tasks!
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Sperry (1968) Split brain study
discussion: Sperry’s conclusions
• apparent doubling of most areas of conscious awareness
• hemispheres appear unaware of each other
• easier to think of two hemispheres as two people
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Sperry (1968) Split brain study
discussion: not a simple tale! • R side could (literally) tell L side what it
knew! • in lab had to be prevented from talking • = sides not so isolated • so personality / intelligence effects limited • some STM / concentration difficulties
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Sperry (1968) Split brain study
discussion
• difficult to generalise!
• variation even between only 11 subjects