Lateralisation

• Lateralisation - the idea that the two halves of the brain are functionally different and certain process or behaviours are controlled by one hemisphere
• Sperry wanted to see what functions of the brain are lateralised, so he compared split brain patients to others without hemisphere separation
• Sperry - the corpus callosum ( connecting the 2 hemispheres ) was cut in patients with severe epilepsy
• Sperry Sight - when an object was presented to the left visual field they could not describe it, but when it was presented to the right they could easily describe it. This is because the language centres are in the left hemisphere.
• Sperry tasks:

  Describe what you see

  Tactile test

  Drawing task
• Sperry describe what you see - a picture was presented to either the left or right visual field and the participant had to describe what they saw
• Sperry tactile test - an object was placed in the patients left or right hand and they had to describe what they felt, or select a similar object from a selection of other objects.
• Sperry drawing task - participants were presented with a picture in the left or right visual field, and they had to draw what they saw
• Sperry describe what you see:

  right visual field - patient could describe

  left visual field - patient couldn’t describe

  This is because the language centres are in the left hemisphere
• Sperry tactile tests:

  right hand - the patient could describe what they felt, or could identify the object presented by selecting a similar object

  left hand - the patient could not describe what they felt, but they could identify it by selecting a similar object
• Sperry drawing tasks:

  right hand - could draw a picture, but it wasn’t as clear as the left hand.

  left hand - the left hand would draw a better picture although all the patients were right handed

  This is because the right hemisphere is dominant for visual and motor tasks.
• AO3. There is research support for lateralisation. There is evidence from Rogers that proves the brain can carry out two tasks simultaneously. He found that chickens could perform 2 tasks at the same time that required both sides of the brain. However, as this research was conducted on animals, it has generalisability and ethical issues. The chicken brain is significantly smaller than the human brain
• AO3. There are individual differences in lateralisation. It can change with age, as you get older your brain becomes more bilateralised, and the hemispheres are not as seperate. This can be linked to functional recovery and neuroplasticity. This shows that lateralisation is not he same in everyone
• AO3. Language may not be restricted to the left hemisphere. TK, a patient that had a damaged left hemisphere was still able to speak and use the opposite hemisphere for support
• AO3. There are methodology issues with Sperry’s research. The procedure to remove the corpus callosum is rarely carried out, so the study cannot be repeated for more up to date findings. These patients may have had pre existing conditions which reduces the internal validity