Hemispheric lateralisation of brain function

• What is hemispheric lateralisation?

  When specialised areas of the brain are found in one of the brain’s hemispheres rather than both.

  E.g. language is processed by the left hemisphere only.
• Describe Sperry' research:

  Sperry studied individuals who had undergone a callosotomy – their hemispheres were separated with a cut down the middle (severing their corpus collosum)
• What was the procedure of Sperry's research?

  • Participants were positioned so that an image could be flashed up in either their left or right visual field.
  • In the “normal” brain, this information would be shared with both hemispheres.
• Findings of Sperry's research - Describing what you see:

  • When an object is shown in a patient’s right visual field, they can name it.
  • However when an object is shown in a patient’s left visual field, they could not name it
• Findings of Sperry's research - Recognising by Touch:

  Even though the patients could not name an object in their left visual field, they could select a matching object hidden behind a screen using their left hand.
• Findings of Sperry's research - Matching Faces:

  • Patients were shown a composite picture made up of two different halves of a face – one half to each hemisphere. When asked to verbally describe what they saw, they would describe the face on the right.
  • When asked to pick a matching picture, they would choose an image that matched the one on the left. 
• Strength - Evidence for difference between hemispheres:

  Sperry's research confirmed that functions are lateralised in the brain and support the view that that the left hemisphere is verbal and analytical and the right hemisphere is adept at spatial tasks and music
• Strength - Methodology used:

  • Standardised procedure
  • Controlled lab experiment
  • High internal validity
• Limitation - Population Validity:

  Only 11 participants took part in all variations of the procedure so results can't be generalised
• Limitation - Participant variables:?

  Some participants' corpus callosum had been more severed than others
• Limitation - Confounding variables:

  The patients all had a history of epilepsy whereas the control group didn't