Sperry (1968) - Lateralisation Of Function

• aim // method

  • aim → to study effects of hemisphere disconnection and to show that each hemisphere has different functions
  • participants → 11 split brain patients with a history of epilepsy & a control group of people with 'normal' brains
  • method → quasi experiment
  • IV → split brain patients or 'normal' group
  • DV → performance on various tasks (that used 1 hemisphere)
• procedure

  → participants sat in front of a screen with hand holes (to cover them)

  → they had an eye patch over one eye (to ensure that visual information was only being presented to ONE visual field at a time)

  → told to fixate on one position on the screen

  → images flashed for 1/10th of a second to either the left or right visual field (to ensure that participants didn't have time to move their eyes as if information was presented to both visual fields ,, it would be processed by both hemisphere of the brain

  → objects were placed in either left or right hand
• method ; design

  → quasi experiments where performance of 11 'split-brain' participants on various tasks was compared with performance of people with no hemisphere deconnection

  → method can also be described as a case study as 11 participants were studied in depth

  • IV - whether a person had hemisphere disconnection or not
  • DV - participants performance on tasks
• method ; participants

  → participants were 11 'split-brain' patients ,, they were patients who had undergone deconnection of cerebral hemispheres because they had a history of advanced epilepsy which couldn't be controlled by medication
• method ; procedure

  → sperry used a number of ingenious tasks in order to investigte lateralisation of brain functions

  • tasks were carried out in LABORATORY CONDITIONS ,, using specialised equipment and were highly standardised
  • the tasks are all involved setting tasks separately to the two hemispheres
• method ; visual tasks ~ 1

  → one of the tasks were used to send information to just one hemisphere involved asking participants to respond to visual information

  • involved blindfolding one of participant's eyes and then asking them to fixate with the 'seeing' eye on a point in the middle of a screen

  
• method ; visual tasks ~ 2


  → researchers would then project an imagine on either the left or right hand side of the fixation point for less than 1/10 of a second

  → presentation time's so small to ensure that participant doesn't have time for eye movement - would 'spread' the info across both sides of visual field & therefore across both sides of the brain

  → as language is processed in the left hemisphere ,, when a stimulus is presented to left visual field of a split-brain patient they shouldn't be able to name the stimulus (as image will be processed only by right hemisphere of brain)

  
• method ; tactile task


  → another of the tasks used to send information to just one hemisphere involved asking patients to respond to TACTILE information

  • this involved preventing a stimulus to one of the hands of a split-brain patient (under a desk so the participant couldn't see the stimulus) & then asking the participant to name it.
  • if stimulus is presented to participants left hand the participant shouldn't be able to name it (because again this information will be being processed by the right hemisphere)
• results ; visual tasks ~ 1

  → images shown in LVF couldn't be named

  • as received in the right hemisphere where there's no language

  → they could draw the image with their left hand

  • as the left hands controlled by the right hemisphere

  
• results ; visual tasks ~ 2


  → here participants would draw a '?' with their left hand ,, as this image was being processed by the right hemisphere

  • which controls the left hand

  → however ,, participants would say they had seen a '$' as this image was being processed by the left hemisphere where language is located

  
• results ; tactile tasks ~ 1


  → the participants wouldn't be able to say what was in their left hand (as this was being processed by the right hemisphere)

  → however ,, if they're given a 'grab bag' ,, they would be able to search with the left hand and retrieve the item

  
• results ; tactile tasks ~ 2


  → if two different objects were placed in both hands at the same time ,, the participants could retrieve the items ,, but each hand would act independently from the other. each hand would search for its own item ,, disregarding what the other hand was searching for

  → split brain patients performed this task more quickly than 'normal' participants

  
• results ; tactile tasks ~ 3

  → the word 'key' is being presented to the LVF ,, which is being processed by the right hemisphere. therefore ,, the participant can select this object with their left hand

  → the word 'ring' is being presented to the RVF ,, which is being processed by the left hemisphere. therefore ,, the participant can say the object is a ring ,, as language is located in the left hemisphere

  
• explanation of results ; 1

  • sperry argued that his study gives considerable support to the argument of laterlisation of function. that is different hemisphere of the brain specialise in different tasks ,, such as he left-hand side being responsible for language

  → sperry found that hemisphere deconnection didn't appear to affect the patient's intelligence (as measured by an IQ test) or their personality. however ,, the surgery did seem to affect the patients in that they had short-term memory deficits ,, limited concentration spans and orientation problems
• explanation of results ; 2


  → in everyday life , split brain patients don't usually notice any difference bc the problems described in this study only occur when visual material is displayed very briefly to only one visual field. the problems are overcome bc a split-brain patient would move their eyes (and therefore the image would be seen by both visual fields) & the image would therefore spread to both hemisphere of the brain. another way that split brain patients overcome their hemisphere deconnection is by saying something out loud so that the info is shared between left & right hemisphere
• evaluation of explanation

  → not all psychologists agree that this study demonstrates lateralisation of function.

  • E.G - some psychologists argue that the two hemispheres do not function in isolation ,, but form a highly integrated system

  → they argue that most everyday tasks involve a mixture of 'left' & 'right' skills

  • E.G. - in listening to speech ,, we analyse both the words and the pattern of intonation ,, thus rather than 'doing' heir own thing the two hemispheres work very much together. there's also some evidence of gender differences whereby women show less laterlisation than men
• evaluation of procedure ; strength

  + A strength of Sperry's procedure was that by using a mixture of quasi-experimental method and clinical case studies ,, he was able to combine qualitative and quantitative approaches. therefore ,, performance on the taks could be easily statistically analused to allow comparisons between split brain and non-split brain patients to be made ,, whilst also gathering the in-depth information on their behaviour
• evaluation of procedure ; weakness ~ 1

  → a major criticism was the small size of the sample ,, with just 11 participants. however ,, sperry didn't really any control over this - there aren't many split-brain patients available to study. the small sample also enabled Sperry to gain more in-depth data ,, by studying the participants in detail

  → study lacks ecological validity. the findings of the study would be unlikely to be found in a real life situation because a person with a severed corpus callosum who had both eyes would be able to compensate for such a loss
• evaluation of procedure ; weakness ~ 2

  →the 11 split-brain patients were lumped together as the experimental group ,, but some of the patients had experienced more deconnection than others. we also can't be sure how long each of the participants had experienced ineffective drug therapy which could have been affecting the findings

  • the control group were people with no inter-hemisphere deconnection. however ,, it could be argued that a much more valid group wouldhave been epileptic people who hadn't had their hemispheres deconnected