split brain research

• what is hemispheric lateralisation?

  behaviours that are controlled by just one hemisphere
• what is an example of hemispheric lateralisation?

  language (controlled by broca/wernicke area) only found in left hemisphere
• what is the corpus callosum?

  a bundle of nerves which allow information to be received by one hemisphere and be sent to the other hemisphere e.g. if a pencil is only seen in left visual field, visual info will be sent to opposite side SO right hemisphere only. however, left hemisphere will still be 'told' about image and person then produces speech about it
• what is a commissurotomy?

  an operation to cut the corpus callosum (to control epileptic seizures)
• what is a person called when they have had a commissurotomy operation?

  a split brain patient
• what was sperry's (1986) procedure for describing what was seen?

  patient would fixate on a dot at the centre of a screen whilst info was presented to the right or left visual field
• what were sperry's (1986) results for describing what was seen?

  when the object was shown to the right visual field, patient could easily describe in words what was seen. however, when the object was shown to the left visual field, the patient would say 'there's nothing there'
• what was sperry's (1986) conclusion for describing what was seen?

  the patient couldn't describe objects shown to the left visual field because the right hemisphere lacks language centres. usually, the messages received by the right hemisphere would be relayed by the corpus callosum to language centres in the left hemisphere
• what was the procedure for sperry's (1986) for recognition by touch?

  objects were shown to the left visual field (image goes to right hemisphere) and the patient was then asked to use one hand or the other to select the object they had been shown
• what were the results for sperry's (1986) for recognition by touch?

  patient cannot name the object (no language centre in right hemisphere) but could select correct object with left hand (controlled by right hemisphere). furthermore, left hand could select an object associated with the image presented to left visual field e.g. an ash train in response to a picture of a cigarette
• what was the conclusion for sperry's (1986) for recognition by touch?


  the patient couldn't verbally identify the object because the left hemisphere is needed for this, but they could understand what the object was using their right hemisphere
• what is the procedure for sperry's (1986) composite words and matching faces?

  a composite word (e.g. key-ring) was split so to parts were shown to separate visual fields (key to left visual field, ring to right visual field)
• what was the procedure for sperry's (1986) composite picture?

  a composite picture of two different halves of a face was presented (one half to each hemisphere)
• what were the results for sperry's (1986) composite picture?

  the left hemisphere dominated verbal description, whilst the right hemisphere dominated the selection of a matching picture
• what was the conclusion for sperry's (1986) composite words and pictures?

  the left hemisphere specialises in speech and language

  the right hemisphere specialises in visual-spatial processing and facial recognition
• what is a positive evaluation point for sperry's split brain research?

  valid - well controlled, standardised procedure e.g. participants fixated on a dot and images flashed for 0.1 seconds so the patient had no time to move their eyes over and transfer info to the other visual field

  valid - shows two hemispheres lateralised to specialise in different functions e.g. left hemisphere = analyser (specialises in analysis + speech) and right hemisphere is the synthesiser (specialises in tasks + music)
• what is a positive evaluation point for sperry's split brain research?


  IRL application in philosophical debate - sperry's research started a debate about the nature of the brain/consciousness. researchers suggested that the hemispheres are so functionally different, we effectively have two minds but others have argued that hemispheres share info and work together on most tasks
• what is a negative evaluation point for sperry's split brain research?

  lacks generalisability - small unique sample of participants as they were all severely epileptic which could've caused unique changes in their brain and influenced findings, cannot apply to non epileptic people

  reductionist + lacks validity - differences in hemispheric function may be over-stated as several tasks associated with one hemisphere can also be carried out by the other when the situation requires it e.g. one hemisphere is damaged by stroke
• what happens when the corpus callosum is cut?

  the left and right hemispheres cannot communicate with each other. e.g. the left hemisphere would not know that there was a pencil in the left visual field, and the person would not be able to speak about it
• what was sperry's (1986) aim?

  to demonstrate that the two hemispheres are specialised for certain functions + could perform tasks independently of one another
• what were the results for sperry's (1986) composite words and matching faces?

  the patient writes key with their left hand (word went to the right hemisphere) but says ring (word went to the left hemisphere)