Sperry

• The key theme is regions of the brain.
• Background

  • The brain is divided into two relatively equal halves, known as the left and right hemispheres.
  • The two hemispheres are joined at the base by commissural fibres, which are bundled into different structures known as the corpus callosum.
  • The fibres convey information between the two hemispheres.
• Background

  • The left and right hemispheres have different sets of functions. This is known as lateralisation of function.
• Background

  The left hemisphere could be described as the "words" hemisphere. It:

  • Controls our ability to speak, recognise and understand words and language
  • Is responsible for logical thinking and reasoning
  • Controls the right side of the body
  • Processes information from the right visual field
  • Processes about 90% of the information from the right ear
• Background

  The right hemisphere could be described as the "pictures" hemisphere. It:

  • Specialises in object recognition, drawing and spatial awareness
  • Also specialises in intuitive tasks
  • Is responsible for artistic creativity and emotional understanding
  • Controls the left side of the body
  • Processes information from the left visual field
  • Processes about 90% of the information from the left ear
• Background

  • The notion that certain brain areas have specific functions is known as localisation of function.
• Background

  • A surgical procedure in which the connecting tissue (corpus callosum) between the two hemispheres was cut was known as a split-brain operation (a commissurotomy).
  • This was done to reduce the frequency and severity of epileptic seizures, which are caused by an electrical storm spreading across the cortex/ many millions of neurons firing.
• Background

  • Sperry believed that patients of commisurotomies showed the true nature of the two hemispheres as the hemispheres are forced to work independently.
• Aim

  Sperry wanted to make use of the opportunity presented by split brain patients to show that:

  • Each hemisphere posses an independent stream of conscious awareness
  • Each hemisphere has its own separate chain of memories that are inaccessible to the other.
• Aim

  • To show that each hemisphere posses an independent stream of conscious awareness
• Aim

  • To show that each hemisphere has its own separate chain of memories that are inaccessible to the other
• • The research Method was a quasi experiment.
• Research Method

  • The research method was a quasi experiment as the naturally occurring independent variable was whether you have a split brain or not. This was not manipulated by Sperry.
  • No control group was actually used as the abilities of non- split brain individuals was already known.
• Research Method

  • The dependent variable was the ability and performance on visual and tactile tasks.
  • It was performed under controlled laboratory conditions.
• Research Method

  • It can also be considered a collection of clinical case studies as a small sample of 11 participants were studied in depth using extensive testing.
• Sample

  • 11 participants who had undergone split brain surgery took part.
• Sample

  • One male had surgery 5 and a half years before the study. One female had surgery more than 4 years before.
  • The other 9 participants had had surgery at varying times, but not long before the study.
  • This is an extraneous variable (potentially more experienced).
• Procedure: presenting visual information

  • Using a tachistoschope, the participant would look at a fixation point on the screen with one eye covered.
  • The visual stimulus would be presented to either the left or right visual field for 0.1 seconds.
  • This prevented participants from moving their eyes and seeing the stimulus with both eyes (therefore processing it with both hemispheres).
• Procedure: Presenting visual information

  • Information was presented to one visual field (left or right) or information was presented to both visual fields simultaneously (left and right)
  • Participants were then asked if they could recognise what they had seen in speech or writing or recognise by pointing to a matching image/object from a collection.
• Procedure: presenting tactile information

  • Below the screen, there was a gap large enough for participants to put their hands under, so they could reach objects without being able to see them.
  • Objects would then be placed in one or both hands.
  • They were asked to find objects, describe in speech objects or point to objects.
  • Participants had to remain in silence during the studies unless they were asked questions by the experimenter.
  • This was to prevent the passing of information from one hemisphere to the other.
• Procedure

  • Participants took part in a variety of both visual and tactile tasks.
• Results

  • Information shown to one visual field could only be recognised again by the same visual field.
  • This is because each hemisphere was unaware of what the other had seen.
  • For example, information taken in by the right visual field would only be processed by the left hemisphere.
• Results

  • Information presented to the right visual field could be described in speech or writing.
  • This is because this information is processed by the left hemisphere, which also controls the right side of the body (right hand) and presenting and understanding of language.
• Results

  • When information was presented to the left visual field, participants insisted they did not see anything so could not describe it in speech or writing. However, they could point to a matching object or image with their left hand.
  • This is because the information was processed by the right hemisphere, which controls the left side of the body (therefore the left hand).
  • The left hemisphere (which is responsible for written and verbal language) was unaware of the information.
• Results

  • If the information $ was presented to the RVF and £ was presented to the LVF, the participant could draw the £ with their left hand, but reported in speech they had seen $.
  • This is because the left hemisphere (responsible for language) processed the $ from the RVF, but was unaware of information presented to the LVF.
  • The right hemisphere (responsible for movement of the left hand) processed the £ in the LVF but was unaware of information presented to the RVF.
• Results

  • If the item was placed into the participant's right hand, it could be identified in speech and writing.
  • This is because the left hemisphere was aware of the item and had the capacity for speech and language, and movement of the right hand.
• Results

  • If the item had been placed in the participant's left hand, it could not be identified by speech but could be selected again by the same hand.
  • The right hemisphere does not have the capacity for language and writing, but can control the left hand (the same hand used to identify the object).
• Results

  • If two different objects were placed in each hand at the same time, then removed and hidden for retrieval in a pile of other test items, each hand would search out its own object when sent to hunt for it. Each hand could be seen identifying and rejecting the object the other hand was looking for.
  • This is because each hemisphere works independently, so both hands work independently.
  • Each hand and hemisphere don't know what the other is looking for so will reject the other's object.
• Result- In the visual tasks, information shown and responded to in one visual field could only be recognised again if shown to the same visual field.


  Conclusion- People with split brains have two separate visual inner worlds, each with its own train of visual images.
• Result- In the tactile tasks, when two objects were placed simultaneously in each hand and then hidden in a pile of objects, both hands selected their own object and ignored the other hand's object.


  Conclusion- Split brain patients seem to have two independent streams of consciousness, each with its own memories, perceptions and impulses (i.e two minds in one body).