Hemisphere Disconnection and Unity in Conscious Awareness Sperry (1968)

Background Information Human brains are divided into hemispheres Lateralization of function: Halves have different functions Ex. Language is carried out in the left hemisphere (for right hand persons)

Lateralization Function or stimulus Right visual field Left visual field Language Left hand Right hand Left ear Right ear Left nostril Right nostril Part of Brain Left Right Left Right Left 90 % right 90% left Left Right

More back ground info Hemispheres joined at their base by commissural fibers- allows for communication Epileptic seizures- patients commissural fibers are cut to prevent effects of seizures to be shared by both sides of brain Roger Sperry took this opportunity to study patients with hemisphere disconnection in order to determine whether there are differences between the two hemispheres of the human brain.

Our visual fields Everything to the left of your nose- left visual field- received to the right of your retinas Everything to the right of your nose- right visual field – received to the left of your retinas

AIM Investigate the effects of hemisphere disconnection and to show that each hemisphere has different functions.

Method/Procedure 11 ‘split brain’ patients- disconnection due to advanced epilepsy natural experiment (quasi) IV- whether a person had hemisphere deconnection or not DV- Participants performance on the tasks Case Study Method (also) All tasks involved setting tasks separately to the two hemispheres.

Task # 1 Visual Information Task Participants blindfolded one eye Fixated vision on a point Flashed a stimuli for 1/10 of a sec What were they testing? If the stimulus was presented to the left visual field, participant should not be able to name it.

Task # 2 Response to tactile information Presenting a stimulus to one of the hands of a split-brain patient Participant could not see the stimulus What were they testing? If the stimulus was presented to the participants left hand, they shouldn’t be able to name it.

Results Task #1- Participants had no recollection of images that were presented to their different visual fields. Task # 1- Participants were not able to give a description of an image that was presented to their left visual field. They were able to point at a similar object with their left hand Task # 1- If two symbols were presented simultaneously….

Results Left Right ? $ -If required to draw with their left hand- symbol on the left -If required to say what they had just seen- symbol on the right

Results Task # 2 Objects in participants right hand- could describe verbally or in writing what the object was Objects in participants left hand- wild guesses or clueless when tested verbally Objects in participants left hand- retrieval was easy when objects were taken away from the participants

Results Task # 2 Different objects placed in both hands Objects taken away and placed in a scrambled pile of test items Participants hunted the initial object that belong to each individual hand

Explanation Sperry argues that his study gives support to his argument of lateralization of function Different areas of the brain specialize on different tasks Each hemisphere has its own perceptions, memories and experiences

Evaluation of Method and Procedure Strengths Combination of quantitative and qualitative data Weaknesses Small sample Control group – he should have considered epileptic patients Ecological validity

Evaluation of Explanation Some psychologists argue that the two hemispheres do not function in isolation but form a highly integrated system. Most every day tasks involve a mixture of right and left skills Some evidence of gender difference. Men show more lateralization than women