Hemispheric Lateralisation & Split brain research

• Hemispheric Lateralisation= the two halves of the human brain are not symmetrical in terms of function.
• The hemispheres of the brain are joined by the corpus callosum- the thick nerve fibres joining the left and right sides of the brain.
• Split Brain Research:

  • By Sperry & Gazzangia (1967)
  • PPs were split brain patients whose corpus callosums had been cut to treat epilespy.
  • Patients told to fixate on dot in the centre of visual field, image flashed onto the screen in either left or right field, and were then asked to state what they had seen.
  • If item presented in left visual field, they were unable to say what they had seen as the information was being processed in the right hemisphere.
  • Allowed conclusion that language centres must be in the left hemisphere.
• Split Brain Research Weakness:

  • Most studies based on a very small sample size.
  • Leads to potentially ungeneralisable results, especially as all had a brain disorder (epilepsy) to begin with.
  • Furthermore, procedure rarely carried out these days, so results cannot be checked via replication.
  • Also not realistic; in real life patients could just use both eyes.
  • Undermines the validity & reliability of the research and what we can conclude from it.
• Split Brain Research Weakness:

  • Sperry & Gazzangia's research has been disconfirmed by most recent research.
  • Original study indicated that the right hemisphere had no language capabilities, but Turk et al documented the case of JW who learnt to walk over time following left hemisphere damage.
  • There is evidence that questions the generalisations of the results of split brain research.
• Hemispheric Lateralisation Strength:

  • Lateralisation has advantages for neural processing capacity.
  • By only using one hemisphere for a task, it means that the other is free to perform a separate function.
  • Rogers et al found that lateralisation in chickens allowed them to look for food & simultaneously stay vigilant for predators.
  • Indicates an evolutionarily sound basis for hemispheric lateralisation.
• Hemispheric Lateralisation Weakness:

  • Lateralisation changes with age- lateralisation found in younger individuals seems to change to bilateral control in older adults, ie language becomes increasingly lateralised in children as they grow into adults.
  • After 25, however, this decreases with age.
  • Cannot be said to be a stable aspect of explaining human behaviour.
• Each hemisphere has specialised functions localised to one half of the brain, and both hemispheres need to share information for effective coordination.
• Contralateral control= each side of the brain controls the opposite side of the body (eg left side of the brain controls right side of the body, and visa versa).