Lateralisation and Split Brain Research

• (A)PFC - Split Brain Research (Sperry and Gazzaniga)


  P - Used split brain patients (corpus callosura is cut)

  • Image/word is projected to the LVF/RVF
  • Describe task - picture presented to LVF/RVF and pp has to describe what they see
  • Drawing task - picture presented to LVF/RVF and pp had to draw what they saw

  F - Describe task — RVS (LH) - could describe what they saw, LVS (RH) - could not describe what was shown

  • Drawing task — RVS (LH) - right hand was never as clear as the left hand, LVS (RH) - left hand drew clearer and better pictures than the right hand
• • What is a split brain patient?

  • Patient that has corpus callosum cut - connects the two hemispheres
  • No communication between hemispheres
• • Hemispheric lateralisation definition

  • The dominance of one hemisphere of the brain for particular physical and psychological functions
  • Left - language
  • Right - visual motor skills
• Lateralisation AO3 - Changes with age


  • Szaflarski et al found that language became more lateralised to the LH with increasing age in children and adolescents, but after the age of 25, lateralisation decreased with each decade of life
  • Lateralisation of function appears not to stay exactly the same throughout an individual’s lifetime, but changes with normal ageing
  • Across many types of tasks and many brain areas, lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults
  • This suggests that lateralisation is not a fixed process
• Lateralisation AO3 - Supporting evidence


  • Assumed that the main advantage of brain lateralisation is that it increases neural processing capacity
  • Rogers et al. found that in a domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators)
  • Using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions. This provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks
• Lateralisation AO3 - Generalisability


  • Because this research was carried out on animals, it is impossible to conclude the same of humans
  • Much of the research into lateralisation is flawed because the split-brain procedure is rarely carried out now so patients are difficult to come by
  • Often the research takes an idiographic approach
  • Therefore, any conclusions drawn are representative only of those individuals who had a confounding physical disorder that made the procedure necessary
  • This is problematic as such results cannot be generalised to the wider population.
• Lateralisation AO3 - Conflicting evidence


  • Recent research has contradicted Sperry’s original claim that the right hemisphere could not process even basic language
  • For example, Turk et al.’s case study of JW found that right after damage to the left hemisphere he developed the ability to speak ‘out of’ his right hemisphere which means he could speak about information presented to either his left or right visual field
  • Suggests that lateralisation is not fixed and the brain can adapt following damage to certain areas