Evalutation of Hemispheric Lateralisation

• strengths

  • related to increased neural capacity
  • scientific methodology
• related to increased neural capacity

  • by using only one hemisphere to engage in a particular task (e.g. language or mathematical ability), this would leave the other hemisphere free to engage in other function and thus increasing neural processing capacity
  • e.g. Rogers et al (2004)- in the domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously- finding food and being vigilant for predators
• related to increased neural capacity COUNTER ARGUMENT 


  it is very hard to apply this finding in animals to human brains. there has been very little evidence showing that lateralisation is advantageous to the functioning of the brain in humans
• scientific methodology 


  the experiments involving split-brain patients made use of highly specialised and standardised procedures. there was a high degree of control over all variables-> increasing the internal validity of the experiement
• scientific methodology COUNTER ARGUMENT

  • many researchers have urged caution in the widespread acceptance of the conclusions drawn from this split-brain research. split-brain patients= an unusual sample of people
  • there were only 11 who took part in all variations of the basic procedure, all of whom had a history of epileptic seizures. this may have caused unique changes in the brain that may have influenced the findings -> lowering the internal validity of the research and making it difficult to draw general conclusions
• limitations

  • differences in function may be overemphasised
  • lateralisation changes with age
• differences in function may be overemphasised

  • one legacy of Sperry's work is that it tends to overemphasise and oversimplify the functional distinction between the left and right hemisphere
  • modern neuroscientists -> the actual distinction between left and right hemisphere is less clear-cut. in the brain the two hemispheres are in communication when performing everyday tasks, and many behaviours associated with one hemisphere can be performed by the other
  • e.g. patient J.W. developed the capacity to speak out of the right hemisphere about information presented each side of the brain.
• lateralisation changes with age

  • lateralisation of function appears not to stay the same throughout a lifetime, but changes with normal ageing
  • Szaflarski et al. (2006)- language became more lateralised to the left hemisphere with increasing age in children and adolescents, but after 25, lateralisation then decreased with each decade of life. across many tasks and and many brain areas, lateralised functions (functions tended to be dealt with by one hemisphere) found in younger individuals tend to switch to bilateral functions (functions dealt with by both hemispheres) in healthy older adults