Brain Laterilisation

• Advantage of brain lateralisation

  • Increases neural processing capacity (the ability to perform multiple tasks simultaneously)
• Evidence for advantages of brain lateralisation

  • In domestic chickens, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators)
• Using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions
• Brain lateralisation can enhance brain efficiency in cognitive tasks
• However, because this research was carried out on animals, it is impossible to conclude the same of humans
• Much of the research into lateralisation is flawed because the split-brain procedure is rarely carried out now, meaning patients are difficult to come by
• Such studies often include very few participants, and often the research takes an idiographic approach (focus on the individual and emphasise the unique personal experience of human nature)
• Any conclusions drawn are representative only of those individuals who had a confounding physical disorder that made the procedure necessary
• Such results cannot be generalised to the wider population
• Furthermore, research has suggested that lateralisation changes with age. Szaflarki et al. (2006) 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

  raises questions about lateralisation, such as whether everyone has one hemisphere that is dominant over the other and whether this dominance changes with age.
• Finally, it could be argued that language may not be restricted to the left hemisphere. Turk et al. (2002) discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, eventually leading to the ability to speak about the information

  presented to either side of the brain. This suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.

   
• Split-Brain Research - Sperry and Gazzaniga ( 1967 )

  • first to investigate hemispheric lateralisation with the use of split-brain features
  • Patients undergone commissurotomy
• Hemispheric Lateralisation - idea that two halves of the brain are functionally different and that each hemisphere has functional specialisations e.g. the left dominant for language, and the right excels at visual motor tasks.

  Two hemispheres are connected through bundles of nerve fibres called corpus callosum, which allows the hemispheres to communicate
• aim: Examine the extent to which the two hemispheres are specialised for certain features
• sample: 11 patients who had epilepsy
• method:

  • Image/word projected to the patient’s left visual field ( which is processed by the right hemisphere ) or the right visual field ( which is processed by the left hemisphere ), 
  • when information is presented to one hemisphere in a split-brain patient, information is not transferred to the other hemisphere ( as corpus callosum is cut )
• DESCRIBE WHAT YOU SEE:

  • picture presented to either left or right visual field, and participate had to simply describe what they saw
• DRAWING:

  • participants presented with picture in either their left or right visual field, and they had to simply draw what they saw.
• FINDINGS: DESCRIBE WHAT YOU SEE

  • Picture presented to right visual field ( processed by left hemisphere )
  • Patient could describe what they saw, demonstrating the superiority of the left hemisphere when it came to language production 
  • Picture presented in left visual field ( processed by right hemisphere )
  • Patient could not describe what was shown and often reported there was nothing present.
• FINDINGS: DRAWING:

  • Picture presented to the right visual field ( processed by left hemisphere )
  • While the right-hand would attempt to draw a picture, the picture was never as clear as the left hand, again demonstrating superiority of right hemisphere for visual motor tasks
  • Picture presented to left visual field ( processed by right hemisphere )
  • Left hand would consistently draw clearer and better pictures than than the right hand ( even though all participants were right-handed )
• CONCLUSION: Findings highlights a number of key differences between the two hemispheres, firstly, the left hemisphere is dominant in terms of speech and language, secondly, the right hemisphere is dominant in terms of visual-motor tasks.
• It is assumed that the main advantage of brain lateralisation is that it increases neural processing capacity (the ability to perform multiple tasks simultaneously).

  Rogers et al. (2004) found that in a domestic chicken, brain lateralisation is associated with an enhanced ability to perform two tasks simultaneously (finding food and being vigilant for predators). Using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions.
• ROGERS

  This provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks.
• However, because this research was carried out on animals, it is impossible to conclude the same of humans.

  Unfortunately, much of the research into lateralisation is flawed because the split-brain procedure is rarely carried out now, meaning patients are difficult to come by. Such studies often include very few participants, and often the research takes an idiographic approach(focus on the individual and emphasise the unique personal experience of human nature.)
• Therefore, any conclusions drawn are representative only of those individuals who had a confounding physical disorder that made the procedure necessary. This is problematic as such results cannot be generalised to the wider population.
• Lacking ecological/population validity

  Along with sample size ( very small - 11 ), restrictive with people that have epilepsy, type of surgery isn’t representative of population as isn’t carried out now

  Patients wore eye patch, given the response that they did when doing tests for the study.
• Furthermore, research has suggested that lateralisation changes with age.

  Szaflarki et al. (2006) 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 raises questions about lateralisation, such as whether everyone has one hemisphere that is dominant over the other and whether this dominance changes with age.
• Finally, it could be argued that language may not be restricted to the left hemisphere.

  Turk et al. (2002) discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere after a car accident, eventually leading to the ability to speak about the information presented to either side of the brain. This suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas.