hemisphere lateralisation

• split brain patients 


  the 2 hemispheres are joined together by tissue - corpus callosum , its the way they communicate
• split brain patients - epilepsy 


  it was proposed that cutting the corpus callosum may benefit people who suffered from severe epilepsy , performing this operation was successful in reducing the severity of epileptic fits - split brain patients provided researchers with an opportunity to study the lateralisation of the brain
• a normal brain

  info from right side of body is processed by left side of brain and vice versa , info then passes across the brain via the corpus callosum so info is shared by the whole brain
• a split brain


  info cannot pass across the corpus callosum so info is only processed by one side of the brain - but the patients are able to lead normal lives because usually they will use both eyes/hands at the same time so the whole brain receives the info
• Sperry 


  1968 - a series of studies which begam in the 1960s - aimed to investigate hemispheric lateralisation in split brain patients - Sperry awarded Nobel prize for this work
• Sperry procedure 


  11 'split-brain' patients , all had corpus callosum cut because of history of epilepsy which couldn't be controlled by medication - Sperry compared the performance of the 11 p's with the performance of 11 people without split brains

  quasi experiment - in laboratory conditions
• Sperry procedure 2

  images or words presented to the left or right visual field - so tasks were set to only one hemisphere

  -p's had one eye covered and instructed to look at a fixed point in the centre of the projection screen

  -pictures were projected at a very high screen (1/10th of a second) tp prevent the p's moving their eye across the picture

  -below the screen was a gap so p's could reach objects but not see their hands

  -when images had flashed on the screen p's were asked to respond verbally or non verbally - by drawing the object / selecting it from under the screen)
• results - describing what you see

  when a picture was shown in the right visual field p's could describe it , if shown to the left visual field the p's could not describe it and reported that nothing was there - because language is processed in the left hemisphere - so objects un L visual field (processed by the right) couldn't be described because of lack of language centres in R hemisphere - in a normal brain the messages would have been relayed to the language centres in the left hemisphere
• results - recognition by touch 


  objects were placed behind a screen so as not to be seen, an image was presented to the left visual field - the p could not respond verbally to this - info went to R hemisphere , but they could select the matching object by touch using their left hand (controlled by R hemisphere)
• conclusion

  Sperry's study supports laterisation of function , different hemisphere of the brain specialise in different tasks - like the left hand side being responsible for language , further trials of the study found that the R hemispheres of the brain is dominant in drawing abilities and facial recognition
• strength - high control 


  the experiments made use of highly specialised and standardised procedures - controlling for extraneous variables
• weakness - the control group

  the control group used was 11 people with no history of epilepsy - could have been more appropriate to use a control group of non-split brain patients with a history of epilepsy - would have stopped history of epilepsy from becoming a confounding variable - so there could be problems with making conclusions based on Sperry's research - unclear whether its the epilepsy or the split brain causing the results
• weakness - generalising 


  issue with an unrepresentative sample , only 11 used in all variation of the basic procedure = small sample size

  all split brain patients had history of epilepsy - been argued that epilepsy may have caused unique changes in the brain that may influence findings - hemisphere laterisation in epileptics may not represent the 'normal' people = issue with generalisation
• weakness - oversimplified

  the differences in function between the hemispheres may be overstated -it overemphasises and oversimplifies the distinction between the hemispheres - neuroscientists would argue that the distinction is less clear cut that Sperry's labels
• weakness - language not restricted - Gazzaniga 


  language might not be restricted to the L hemisphere , Gazzaniga = some of the early discoveries from split brain research have been disconfirmed by more recent discoveries - example , split brain suggested that the R hemisphere is unable to handle basic language but case studies suggest its not the case = J.W developed the capacity to speak out of the right hemisphere and can now soeak about info presented to the L or R brain