hemispheric lateralisation

• Laterilisation refers to the fact that some mental processes in the brain are mainly specialised to either the left or right hemisphere
• Left hemisphere - responsible for speech and language
• Right hemisphere - responsible for spatial awareness, music and visual processing
• Right hemisphere - responsible for spatial processing and facial recognition
• Split brain research studies individuals who have had surgical separation of the two

  hemispheres of the brain as a result of severing the corpus callosum.
• Sperry and Gazzaniga's split brain research studied the capabilities of split brain patients. Because information presented to the left visual field is processed in the right hemisphere and information presented to the right visual field is processed in the left hemisphere.
• corpus callosum is cut in split brain patients, the information cannot travel to the other hemisphere
• Sperry Method-

  Information presented to either the right or left visual field.

  They were asked to make responses with either their:

  left hand (controlled by right hemisphere)

  • Right hand (controlled by left hemisphere)
  • Verbally (controlled by left hemisphere)
• If the pictures were presented to the right visual field all patients could say and write what they

  had seen without a problem. (as processed in left hemisphere that has a language centre)
• If the pictures were presented to the left visual field the participants could not say or right what

  they had seen, but they could draw what they had seen with their left hand. (processed in the

  right hemisphere which does not have a language centre so cannot say they saw it, but it does

  process visual information so they can draw it)
• Language may not be restricted to the left hemisphere


  case study of J.W who developed the capacity to speak out of the right hemisphere

  after suffering an injury to his left hemisphere, regardless of which side of the brain the

  information is presented to.
• What happens to lateralisation of function as individuals age?


  Lateralisation changes with age
• How does lateralisation of function differ between younger individuals and healthy older adults?


  Many lateralized patterns in younger individuals switch to bilateral patterns in healthy older adults
• What trend was observed regarding language lateralisation in children and young adolescents?


  Language became more lateralized to the left hemisphere with increasing age
• What happens to lateralisation after the age of 25?


  Lateralisation decreases with each decade of life after the age of 25
• What is one explanation for the decrease in lateralisation with age?


  Using extra processing resources of the other hemisphere may compensate for age-related declines in function
• What are the key changes in lateralisation of function throughout a person's life?


  • Lateralisation changes with age
  • Younger individuals show more lateralized patterns
  • Healthy older adults tend to have bilateral patterns
  • Language lateralisation increases in children and young adolescents
  • After age 25, lateralisation decreases with each decade
  • Compensatory use of the other hemisphere may occur
• Limitations of split brain research Split brain operations are a rare procedure, therefore patients who have had the procedure are rarely encountered in sufficient numbers to be useful for research. I.e because the individuals had very specific disorders it may not be possible to generalise the findings of the studies to the wider population
• Lateralisation and immune system function Architects and mathematically gifted tend to have superior right-hemispheric skills but are also more likely to be left-handed and to suffer higher rates of allergies and problems with their immune system. E.g Tonnessen et al found a significant relationship between handedness (using either your right or left hand) and immune disorders, which suggests that the same genetic processes that lead to lateralisation may also affect the development of the immune system