Lateralisation and split-brain research

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  • Lateralisation and split-brain research
    • Hemispheric  Lateralisation
      • Lateralisation refers to the fact that the two halves of the brain are not exactly alike
      • Each hemisphere has functional specialisation
        • Research has found the left  hemisphere is dominant for language and speech and the right excels at visual-motor tasks
          • The 2 hemispheres are connected this allows information received by 1 hemisphere can be sent to the other through connecting bundles of nerve fibres
            • In treatment for severe epilepsy surgeons cut the bundle nerve fibres that formed the corpus callous. The aim of this was to prevent the violent electrical activity crossing the hemispheres.The patient that underwent this procedure were referred to as split-brain patients
    • Split Brian research
      • Sperry and Gazzaniga's research
        • The first to study the capabilities of the separated hemispheres
          • In a typical study, the split-brain patient would fixate on a dot in the centre of a screen while information was presented to either the left or right visual field
            • They would be asked to make responses with either their left or right hand, or verbally
              • Information from the left visual field is processed by the right hemisphere which can see the picture, but has no language centre so cannot respond verbally
                • The left hemisphere which has a language centre does not receive information about seeing the picture so cannot say it has seen it
      • What have we learned from split brain research?
        • Split brain research has not shown that the brain is organised into discrete regions with specific areas for specific tasks
          • It has instead suggested that the connectivity between the different regions is as important as the operation of the different parts
    • Evaluation
      • Advantages of hemispheric lateralisation:
        • Very little  empirical evidence has been provided to show that lateralisation is associated with an enhanced ability to perform 2 tasks simultaneously
          • This finding does provide some evidence that brain lateralisation enhances brain efficiency in cognitive tasks that demand the simultaneous but different use of both hemispheres
      • Lateralisation and immune system functioning:
        • People who are mathematically gifted are more likely to be left-handed and often suffer higher rates of allergies and problems with their immune system
          • Tonnessen found a small but significant relationship between handedness and immune disorders, this suggests that same genetic processes that lead to lateralisation may also affect the development of the immune system
      • Lateralisation changes with age:
        • 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
          • Szaflarski found that language became more lateralised to the left hemisphere with increasing age in children and adolescents
            • After the age of 25 lateralisation decreased with each decade
              • A possibility of this is that using the extra processing resources of the other hemisphere in some way may compensate for age related declines in function
      • Language may not be restricted to the left hemisphere:
        • Gazzaniga suggests that some of the early discoveries from split brain research has been disconfirmed by more recent discoveries
          • Split brain research had suggested that the right hemisphere was unable to handle language however case studies have demonstrated that this was not necessarily the case
            • A patient know as J.W developed the capacity to speak out of the right hemisphere
      • Limitations of split brain research:
        • The procedure is rarely carried out today therefore patients who have had the procedure are rarely encountered to be useful for research
          • Andrews argues that many studies are presented with as few as 3 PP's therefore he claims conclusions have been drawn from individuals who have a confounding physical disorder or have had a less complete sectioning of the 2 hemispheres than was originally believed
            • He claims that these rogue cases are often only identified when results of the study have failed to be replicated


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