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