Lateralisation/split brain research

• Lateralisation :

  • the idea that neural mechanisms for some functions are located in only one main hemisphere
  • Left tends to dominate in language and speech
  • Right tends to dominate in visual-motor tasks
• Hemispherical communication:

  • the hemispheres are connected, allowing us to do things like verbally explaining things we have seen in our left visual field
  • info passed through bundle of fibres called corpus callosum
  • In treatments for severe epilepsy, sometimes corpus callosum is cut, resulting in split brain patients
• Sperry and Gazzaniga 1967:

  • first to study split brain patients
  • in typical study, P would focus on a dot in centre of a computer screen, then images would flash either to the left or right
  • Items in the left visual field are processed by the right hemisphere, and vice versa
• Sperry and Gazzaniga 1967:

  results

  • Objects like a cat presented to the left visual field resulted in Ps saying they say nothing
  • Objects like a dog presented to the right visual field resulted in the Ps saying dog
  • The info from the LVF is processed by the right hemisphere, which cannot communicate with the language centres in the left - this is why the P cannot say they saw anything
• AO3 lateralisation

  • Main strength is that it increases neural processing capacity
  • by using only one hemisphere for a task, the other is free to focus on other things
  • little empirical evidence to suggests lateralisation confers any actual advantage for brain functioning
  • Rogers 2004 - in domestic chickens, brain lateralisation is associated with enhanced abilities, eg finding food and being vigilant or predators simultaneously
• AO3 lateralisation:

  • those like mathematicians and architects wiypth enhanced right hemispheres are more likely to be left handed and suffer higher rates of allergies/suffer immune system issues
  • Tonnessen 1993 - small yet significant relationship between left handedness and immune system disorders
  • This suggests the same genetic processes that lead to lateralisation may also affect development of the immune system
  • Morfit and Weekes 2001 - left handers had higher incidence of immune system disorders in their immediate family than right handers
• AO3 lateralisation:

  • Laterised patterns in younger people tend to switch to bilateral as they become healthy older adults
  • Szaflarski 2006 - language became more laterised to the left with increasing age in children and adolescents, but lateralisation decreases after age 25, decreasing more in subsequent decades
• AO3 Split brain patients:

  • Gazzaniga 1998 suggests early split brain discoveries have been disconfirmed with more recent studies
  • Damage to left far more detrimental to language than damage in right
  • However, JW case study (Turk 2002), developed capacity to speak out of right hemisphere
  • Challenges the claim that right hemisphere unable to handle even rudimentary language
• AO3 split brain patients:

  • Andrewes 2001, split brain procedure so rare nowadays, that many studies are presented with as small as one-three Ps
  • In some cases, conclusions have been drawn from from Ps with already confounding physical disorders (which led them to the split procedure in the first place)
  • Claims that some Ps hemispheres may have been less completely split than initially believed
  • Ps without any of these confounding factors too little in number to be useful in research