laterisation and split brain research

• the term brain lateralisation refers to the fact that the two halves of the human brain are not exactly alike. each hemisphere has functional specialisations.
• Broca established that damage in a particular area of the left brain hemispheres led to language deficits, yet damage to the same area of the right hemisphere did not have the same consequence.
• research has found that the left hemisphere is dominant for language and speech, whereas the right excels at visual-motor tasks.
• the two hemispheres are connected, which allows information received by one hemisphere to be sent to the other hemisphere through connecting bundles of nerve fibres such as the corpus callosum.
• Sperry(1967), tested the capabilities of split-brain patients. they were able to send visual information to just one hemisphere at a time in order to study hemispheric lateralisation.
• because the corpus callosum is cut in split-brain patients, the information presented to one hemisphere has no way of travelling to the other hemisphere and is only processed in that specific hemisphere.
• in a typical study, the 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 then be asked to make responses with their left hand (right hemisphere), or right hand (left hemisphere), or verbally(left hemisphere), without being able to see what their hands were doing.
• for example, if the patient was flashed a picture of a dog in the right visual field and asked what they had seen, they would answer dog. However, if shown in the left visual field the patient would say they see nothing.
• What is a drawback of lateralisation?

  It changes with age.
• How do lateralised patterns in younger individuals change as they age?

  They tend to switch to bilateral patterns in healthy older adults.
• What did Szaflarski et al. find regarding language lateralisation in children and adolescents?


  Language became more lateralised to the left hemisphere with increasing age.
• What happens to lateralisation after the age of 25 according to Szaflarski et al.?


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


  Using the extra processing resources of the other hemisphere may compensate for age-related declines in function.
• Why is it difficult to know why lateralisation changes with age?

  There is no clear explanation for the changes observed.