hemispheric lateralisation and split-brain research

• What is lateralisation?

  The idea that two halves of the brain are functionally different and that each hemisphere has functional specialisation (left is dominant for language and the right excels at visual motor tasks)
• What is each side of the brain responsible for?

  Left - dominant for language centres

  
  

  Right - dominant for visual motor tasks
• What are the two hemispheres connected through?

  They are connected through nerve fibres called the corpus callosum
• What does the corpus callosum do?

  Facilities inter hemispheric communication - allowing the left and right hemisphere to talk to one another
• Who are the key researcher involved in split brain research?

  Sperry and Gazzaniga (1967)
• What were Sperry and Gazzaniga (1967) the first to investigate?

  The first to investigate hemispheric lateralisation with the use of split brain patients
• Give some background into split brain patients

  Individuals who have undergone a surgical procedure where the corpus callosum is cut

  
  

  This procedure, which separates the two hemispheres, was used as a treatment for severe epilepsy
• What is the surgery called used to separate the two hemispheres

  Corpucallosotomy
• Who is split brain surgery used to treat?

  Severe epilepsy
• What was the aim of Sperry and Gazzaniga (1967) split brain research?

  The aim of their research was to examine the extent to which the two hemispheres are specialised for certain functions
• What is the method that Sperry and Gazzaniga (1967) used?

  - an image/ word is projected to the patients left visual field or the right visual field

  
  

  - when information is presented to one hemisphere in a split brain patient, the information is not transferred to the other hemisphere since the corpus callosum is cut
• What were the three different experiments that Sperry and Gazzaniga (1967) used?

  1. Describe what you see

  2. Tacticle test

  3. Drawing task
• When information is projected to the participants left visual field what side of the brain processes this?

  The right hemisphere
• Describe the 'what you see tasks'?

  A picture was presented to either the left or right visual field and the participant had to simply describe what they saw
• Describe what you see task: what happened when the picture was presented to the right visual field?

  The patient could describe what they saw, demonstrating the superiority of the left hemisphere when it comes to language production
• Describe what you see task: what happened when the picture was presented to the left visual field?

  The patient could not describe what was shown and often reported that there was nothing present
• Describe the 'tactile test'

  An object was placed in the patients left or right hand and they had to either describe what they felt or select a similar object from a series of alternate objects
• Tactile test: what happened when the object was placed in the right hand?

  The patient could describe verbally what they felt

  
  

  or they could identify the test object presented in the right hand (left hemisphere) by selecting a similar appropriate object from a series of alternate objects
• Tactile test: what happened when the object was placed in the left hand?

  The patient could not describe what they felt and could only make wild guesses

  
  

  However, the left hand could identify a test object presented in the left hand (right hemisphere) by selecting a similar appropriate object from a series of alternate objects
• Describe the 'drawing task'

  Participants were presented with a picture in either their left or right visual field and they had to simply draw what they saw
• Drawing task: what happened when a picture was presented to the right visual field

  While the right hand would attempt to draw a picture, the picture was never as clear as the left hand which demonstrated the superiority of the right hemisphere for visual motor tasks
• Drawing task: what happened when a picture was presented to the left visual field?

  The left hand (controlled by the right hemisphere) would consistently draw clearer and better pictures than the right hand (even though all the participants were right handed)

  This demonstrates the superiority of the right hemisphere when it comes to visual motor tasks
• What were the conclusions made from Sperry and Gazzaniga's split brain research?

  The findings of Sperry and Gazzanignas research 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
• Essay structure plan for 'outline and evaluate research into lateralisation and/ or the split brain' (16 marks)

  A01 - lateralisation (define)

  A01 - Sperry and Gazzaniga (aims, method, results ,conclusion)

  
  

  A03 - evidence - multitasking (rogers et al 2004, chickens find food and check for predators)

  
  

  A03 - methodological criticism- small sample (sperry and Gazzaniga only examined 11 patients and all suffered from epilepsy) (idiographic approach)

  
  

  A03 - language in the right hemisphere (Turk et al 2002, patient JW spoke from the right hemisphere)
• Split brain research/ lateralisation evaluation - multitasking

  P - one of the main advantages of brain lateralisation is that it increases neural processing capacity (the ability to multitask)

  
  

  E - rogers et all (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)

  
  

  E - using only one hemisphere to engage in a task leaves the other hemisphere free to engage in other functions

  
  

  L - this matters because it provides evidence for the advantages of brain lateralisation and demonstrates how it can enhance brain efficiency in cognitive tasks
• Split brain research/ lateralisation evaluation - methodological criticism


  P - a limitation of the research into lateralisation is that some is flawed because the split brain procedure is rarely carried out now meaning patients are difficult to come by

  
  

  E - Sperry and Gazzaniga's research only included 11 patients all of which had varying degrees of epilepsy

  
  

  E - such studies often include very few participants

  
  

  D - consequently, some psychologists have argued that Sperry's research is really a collection of case studies that take an idiographic approach. Although an idiographic approach provides rich and interesting information in relation to individual cases, we are unable to create general laws as found in nomothetic research

  
  

  L - this matters because any conclusions drawn are representative only of those individuals who had a cofounding physical disorder that made the procedure necessary. This is problematic as such results cannot be generalised to the wider population
• Split brain research/ lateralisation evaluation - language in the right hemisphere

  P - it could be argued that language may not be restricted to the left hemisphere

  
  

  E - Turk et al (2002) discovered a patient (J.W) that suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere

  
  

  E - eventually leading to the ability to speak about the information presented to either side of the brain

  
  

  L - this matters because it suggests that perhaps lateralisation is not fixed and that the brain can adapt following damage to certain areas
• lateralisation in connected brain

  P: strength - hemisphere work differently even though conected

  E: when ppts with conected brains asked to look at global elements of a picture, RH was more active

  E: when ppts were asked to look at finer details, LH was more dominant

  L: therefore hemispheric lateralisation is present in a connected brain
• one brain - lateralisation

  P: limitation - LH as analyser and RH as synthesiser may be wrong

  E: researcher analsyed brain scans from over 1000 people aged 7-29 and found evidence for lateralisation

  E: however there was no evidence of a dominant side i.e. no artists brain

  L: therefore notion of left-brained or right brained people wrong
• research support - split-brain research

  P: strength - research support

  E: split-brain patients performed better than connected patients at some tasks

  E: in normal brain, LH's better cognitive strategie are watered down by inferior RH

  L: therefore this supports sperrys idea of the right brain and left brain being distinct
• generalisation issues

  P: limitation - causal relationships hard to establish

  E: confounding variable - split-brain patients compared to neurotypical control patients

  E: differences between the two groups may be due to epilepsy rather than split brain

  L: therefore uniques features of split-brain patients may be due to epilepsy