Hemispheric Lateralisation and Split Brain Research

• Corpus Callosum


  bundle of nerve fibres which joins the 2 halves of the brain.

  - commissurotomy - division of the 2 hemisphere by surgery, which as occasionally been done to improve epilepsy.
• Left Hemisphere


  - language centre of the brain

  - control the right hand

  - receives info from the right visual field.
• Right Hemisphere


  - focuses on visuo-spatial tasks

  - control the left hand

  - receives info from the left visual field.
• Hemispheric Lateralisation


  2 hemisphere of the brain are functionally different. certain mental processes are controlled by one hemisphere
• Sperry's Split Brain Experiment

  - quasi experiment

  - 11 ppts

  - patients were epileptics -> already had their corpus callosum removed (no ethical issues).

  - gazed at a fixation point on a translucent screen.

  - slides are projected either side of the fixation point at a rate of 1 picture per 1/10s.

  - tacile task -> carried out with ppts hand underneath a screen.

  - study suggested each hemisphere had completely separate functions

  - Sperry conducted a number of variations:

  1. Describing what you see

  2. Recognition by touch

  3. Composite words

  4. Matching faces
• Strength - research support

  research supports the lateralisation of the brain.

  right = synthesiser.

  left = analyser

  right is responsible for spatial awareness, left is responsible for language.
• Strength - controlled procedure

  Sperry's procedure was a standardised controlled one. it was also unique allowing him to test a number of functions.
• Weakness - research against

  Pucetti - hemispheres are dual in all brains. we have split minds.

  these differences are just exaggerated in Sperry's split brain patients (weakness of Sperry's research, but strength of lateralisation.

  - stimulated a debate between whether the brain is lateralised or whether the hemispheres perform similar functions.
• Weakness - limited sample

  - all epileptics and only 11.

  - could the seizures have influenced the brain and the findings?

  - poor generalisability?
• Weakness - lateralisation isn't clear cut

  - lateralisation and functions aren't as clear cut (language/non language is a basic distinction) - some functions can be shared by different areas of the brain through constant communication.

  e.g. during functional recovery.

  - lateralisation is overestimated.