Lateralisation of function in brain

• Lateralisation 


  the left and right hemisphere are responsible and specialised to perform certain functions.
• Sperry and Gazzaniga - lateralisation of language 


  -Procedure: split brain patients were tested in lab conditions. PP stared at a focal point and words were briefly flashed to the left/right visual field. Then PP were asked what they saw.

  -Results: when words are presented to RVF PP could state the image or word. But if the same word was presented in LVF PP reported seeing nothing but could draw object with left hand.

  -Conclusion: PP were able to state words presented in the RVF but Sperry concluded language is lateralised to LH and RH has limited language functioning.
• Lateralisation of facial processing

  -Procedure: Split brain patients tested in lab conditions. PP stared at a focal point and were briefly flashed images of a composite face. Half the face was in LVF and different face presented to the RVF. PP's were asked to match the image to the face they saw.

  -Results: PP's selected images of people who matched the face presented to LVF.

  -Conclusion: function of recognising faces and spatial images is lateralised to the RH. PP constantly selected the image of the face presented to LVF, processed by RH.
• Sperry and Gazzaniga - split brain research strengths

  +Standardised procedure: Lab conditions using scientific method. e.g. what visual stimuli were presented, which visual field and how long. Allows for replication and and can assess reliability.

  +High internal validity: Sperry's research done in controlled lab conditions. Visual restrictions and briefly presented info to LVF/RVF reduces influence of extraneous variables. Findings that the LH is specialised in language is high in internal validity .
• Sperry and Gazzaniga - split brain patients weaknesses

  -Lacks ecological validity: Sperry used procedures which lacked mundane realism. In real life a severed corpus collosum is compensated by the unrestricted movement of both eyes. Findings don't contribute to understanding LH/RH in everyday life.

  -Small sample: 11 split brain patients and single case studies (Karen) so there's issues with generalisation about lateralisation of functions of the LH/RH. Leads to population validity.
• Split brain research 


  -In neurotypical people the LH and RH share information via the corpus collosum, making studying lateralisation of function difficult.

  -Split brain patients had corpus collosum severed to reduce epileptic seizures. This prevents the LH and RH from sharing information allowing research about lateralisation to take place.

  -Using a tachyscope allows info to be sent and processed by either LH or RH by flashing images/words to RVF or LVF.

  -Info presented to the LVF is processed by RVA in the RH and info presented to the RVF is processed in LVA and LH.
• Testing split brain patients

  -Sperry studied 11 individuals. In controlled lab conditions PP were asked to share at a central focal point. Images/words would flash for a second to the left/right visual field via tachistoscope.

  -In split brain patients info is processed solely by the LH or RH.

  -PP would then be asked to do a series of tasks like say/describe what they had seen or select matching objects.

  -Behavioural response of patients are recorded and compared to a control group.
• Evaluation


  +Case study of Karen Byrne who was a split brain patient. When waking from surgery Karen's left side had functional independency and had no conscious awareness from Karen. Alien hand syndrome. Her left hand operated beyond her conscious control. Suggesting the left/right hemispheres function contralaterally and have their own independent consciousness.

  -Confounding variables: some split brain patients have been on drug therapy to treat epilepsy. Functional changes in the brain from epilepsy sufferers may have taken place.