Lateralisation

• Corpus Callosum

  • Bundle of nerve fibres which joins the two halves of the brain
  • A commissurotomy is the division of the two hemispheres by surgery which has occasionally been done to improve epilepsy
  • left and right side communicates through the corpus callosum
• left visual field -> right hemisphere -> left hand

  right visual field -> left hemisphere -> right hand
• sperry's split-brain experiment (1968)

  • Quasi experiment
  • 11 participants
  • Sperry's participants were epileptics who could not be treated with drugs - they already had their corpus callosum split
• Split brain procedure

  • participant gazes at a fixation point on an upright translucent screen
  • slides are projected either side of the fixation point (into one visual field or the other) at a rate of one picture per 1/10 second.
  • participants asked to recall what they had seen in different ways: verbally, drawing, touch recognition
• A03 Lateralisation changes with age

  • lateralisation function is not exactly the same through an individual's lifetime -> changes with normal ageing
  • Lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults
  • Szaflarski found that language became more lateralised to left hemisphere with increasing age in children and adolescents - after age 25, lateralisation decreased with each decade of life
• A03 supporting evidence of lateralised functions in 'normal' brains

  • Fink used PET scans to show which brain areas were active during a visual processing task
  • scans showed right hemisphere was more active when participants asked to focus on global elements of an image. Left hemisphere more active when participants asked to focus on finer details of an image. Lateralisation is a feature of normal brain as well as split brain
• A03 lateralisation and immune system functioning

  • number of disadvantages associated with hemispheric lateralisation
  • architects and mathematically gifted tend to have superior right hemispheric skills but more likely to be left handed and suffer higher rates of allergies and problems with immune system.
  • Tonnessen found a small but significant relationship between handedness and immune system disorders - same genetic processes lad to lateralisation may also effect development of immune system
• A03 limitation of Sperry's research is that it is difficult to establish a cause and effect relationship

  • In Sperry's study the behaviour of split brain participants was compared to a neurotypical control group
  • Participants in control group didn't have epilepsy. any differences between groups may be due to epilepsy not the split brain - this is a confounding variable
  • this means some of the unique features of the split brain participants cognitive abilities might have been due to their epilepsy