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Sperry 1968 Hemispheric deconnection (Background (Brain is lateralised -…
Sperry 1968 Hemispheric deconnection
Background
Brain is lateralised - each side is 'specialised' for certain behaviours
Left side dominant for language production and logical thought
Right side dominant for visual imagery, spatial awareness and facial recognition
Left side controls ride side of body, right side controls left side of body
Operation offered to severe epileptics where severe corpus callosum (commissurotomy) to prevent spread of seizures from one hemisphere to the other
AIM - to investigate the effects of hemispheric deconnection of perception and memory
Research method
Series of case studies - intensive study of 11 patients with hemispheric deconnection
Quasi experiment - IV naturally occurring (presence or absence of split-brain)
DV - participants performance on tasks
Independent measures - participants only take part in one condition (split brain or non-split brain)
Sample
Opportunity sample of hospital patients referred to White memorial centre in LA (where he worked)
11 American patients who had undergone a commissurotomy for severe epilepsy
1 male who's surgery was 5.5 years before study, 2 mothers more than 4 years before and others surgery not long before study
Procedure
Participant had one eye covered and was asked to look at a fixed point in the centre of a projector screen below the screen was a gap so the participants could reach objects but not see their hands
Visual task(1) - visual stimuli projected on screen to either left or right visual field for just 1/10th of a second (using
tachistoscope
so only one eye could process image) the participants was then asked to identify what they saw through speech, writing or drawing
Visual task(2) - two stimuli flashed simultaneously to different visual fields and participants were asked to identify what they saw through speech, writing or drawing
Tactile investigations - object was placed in either left, right or both hands without the participants being able to see what they're holding, then asked to identify what they were holding through speech, writing, drawing or manual selection from various objects
Test of RH - right hemisphere doesn't produce language so to test mental ability number of tests undertaken: simple math problems were presented to the left visual field, geometric shapes presented to both visual fields and a nude presented in the middle of the objects only to the left visual field
Key findings
Visual task 1 - participants were couldn't give a description of image presented to left visual field but could point to it with their left hand or draw it with their left hand
Visual task 2 - if participant required to draw with their left hand what they'd seen they would draw the left visual field symbol (shielded from own view). If they were required to say what they'd just drawn they would say the right visual field symbol
Tactile tasks - if an object was placed into RH could identify it verbally but not if it was in LH however could find it by touch with LH from bag of objects
when objects palced in one hand coud point to what object was with same hand
When participants hand placed in certain position by experimenter couldn't replicate it with other hand
Test of RH - right hemispheres able to carry out simple math problems - when participants saw geometric shapes would giggle or look embarrassed when nude appeared even though they couldn't explain why
Conclusions
Split brain patients have lack of cross-integration, second hemisphere has no idea what first hemisphere has been doing
Split brain patients have two independent steams of consciousness each with its own memories, perceptions and impulses
People with split brains have two separate visual inner worlds