HEMISPHERIC LATERALISATION / SPLIT BRAIN

• HEMISPHERIC LATERALISATION 


  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 processing and facial recognition
• 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.
• SPLIT BRAIN RESEARCH 


  SPERRY studied the capabilities of split brain patients.
• SPLIT BRAIN RESEARCH 


  involves individuals who have had surgical separation of their brain hemispheres by cutting their corpus callosum , in order to relieve symptoms of severe epilepsy. This meant that in split brain patients, the information cannot travel to the other hemisphere. I.e info from the left visual field can only be processed in the right hemisphere. Method Information presented to either the right or left visual field
• SPLIT BRAIN RESEARCH


  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 the left hemisphere that has a language centre)
• SPLIT BRAIN RESEARCH 


  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).
• (+) HL 


   research showing that even in connected brains the two hemispheres process information differently. FINK ET AL used PET scans to identify which brain areas were in action during visual processing tasks. When asked to focus on global elements of an image, regions of the RH were active. When focussing on the finer details, the LH tended to dominate. This suggests that for visual processing, hemispheric lateralisation is a feature of the connected brain as well as the split-brain.
• (+) HL

  Lateralisation is adaptive because ROGERS ET AL found that, in the domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously - finding food and being vigilant for predators. 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.
• (-) HL 


  LH as analyser and RH as synthesiser may be wrong. Nielsen et al analysed brain scans from over 1000 people aged 7 to 29 years and found that people used certain hemispheres for certain tasks(lateralisation). But there was no evidence of a dominant side, ie) not artists or mathematicians' brains. This suggests that the notion of right or left brain people is wrong.
• (-) HL 


   lateralisation changes with age. SZAFLARSKI ET AL found that language became more lateralised to the left hemisphere with increasing age in children and adolescents, but after the age of 25. Lateralisation decreased with each decade of life. This suggests that the extra processing resources of the other hemisphere may compensate for age-related declines in function. 
• (+) SPLIT BRAIN 


  SPERRY'S work has prompted a theoretical + philosophical debate about the degree of communication between the 2 hemispheres and the nature of consciousness. PUCCETI suggests = 2 hemispheres are so functionally different that they represent a form of duality in the brain (we are all two minds). Other researchers have argued that 2 hemispheres form a highly integrated system (holistic) and are both involved in most everyday tasks. suggests = split brain research has been useful in our understanding of the role of each hemisphere and the extent to which they are localised. 
• (+) SPLIT BRAIN 


  LUCK ET AL =

  They showed that the split brain participants actually performed better on certain tasks. eg) they were faster at identifying the odd one out in an array of similar objects than normal controls. This supports Sperry’s earlier findings that the left brain and right brain are distinct.
• (-) SPLIT BRAIN 


  METHODOLOGICAL WEAKNESS =

   The lack of internal validity. This is because the length of the cut to the corpus callosum varies between individuals. Andrews et al also found that conclusions have been drawn from individuals who either have a confounding physical disorder that made the split-brain procedure necessary, or have had a less complete sectioning of the two hemispheres than was originally believed. 
• (-) SPLIT BRAIN 


  Language is not restricted to the left hemisphere only. The case study of JW 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.