Sperry - Brain regions

• What was the background?

  • The brain is divided into 2 hemispheres which communicate through a connection called the corpus callosum  
  • Localisation of function is 1 area of the brain and lateralisation of function is where half of the brain is responsible for a function 
  • There is an operation to disconnect hemispheres by cutting through the corpus callosum and this procedure is called a commissurotomy. This means that both sides of the brain operate as 2 independent brains  
  • This causes issues for functions that are cross wired
• What was the aim?

  • To record psychological effects of hemispheric deconnection in patients with severe epilepsy 
  • To use results to understand how the right and left hemispheres work in “normal” individuals 
• What was the sample?

  • 11 split brain patients with severe epileptic seizures 
  • Opportunity sample of patients referred to white memorial centre in Los Angeles 
• What were the materials?

  Tachistoscope – device that shows image for specific amount of time (projects backwards) and below the projector screen there was a gap so ppts could reach objects but not see them 
• What was the procedure?

  • Ppts seated in front of screen and asked to focus on cross (cross is for reliability) in the middle and one eye is covered 
  • Images flash for 0.1 seconds which only gave time to process image in the visual field it is placed 
  • Completed tasks to test how right and left hemispheres respond to input from left visual field and right visual field, and left and right hand 
• What was task 1?

  • Recognition of visual stimuli presented to left and right hemispheres separately 
  • Visual stimulus of picture of object was presented to the left visual field or right visual field, ppt was shown same image again to either the same or other visual field and asked whether they recognised the object 
• What was task 2?

  •  Responding with speech to visual stimuli to left and right hemispheres separately 
  • Visual stimulus presented to either left visual field or right visual field and ppts asked to describe visual stimulus 
• What was task 3?

  • Responding in writing to visual stimuli presented to left and right hemispheres separately 
  • Test identical to second except ppt required to write name of stimulus rather than saying it  
• What was task 4?

  • Responding by pointing to visual stimuli to left and right hemispheres separately 
  • Test was also identical to second test except ppt required to point to the stimulus seen 
• What was task 5?

  • Responding to stimuli presented to left visual field and right visual field of hemispheres at the same time 
  • 2 different figures flashed simultaneously with one to the left visual field and the other to the right visual field, the ppt was asked to draw with their left hand what they had seen. They then had to say what they had drawn without looking  
• What was task 6?

  • Recognition of pairs of related words presented visually and simultaneously to the left and right hemispheres 
  • The words were composed of 2 smaller words presented to the ppts so that half of the word fell into the left visual field and the other half in the right visual field 
  • They indicated recognition in 3 ways Ppt could use 1 hand to search through objects from hidden view Say the name of the object Write the name of the object down 
• What was task 7?

  • Verbal identification of objects placed in hands 
  • Ppt prevented from seeing objects in left or right hand. They were then asked to say or write the name of the object they had held or retrieve object held using either left or right hand 

   
• What were the results?

  • To right visual field: 

  - Can describe in speech and writing

   - Can point with right hand 

  - Can find with right hand  

  • To left visual field: 

  - Unable to name object 

  - Point with left hand 

  - Find with left hand 

   
• What were the conclusions?

  • Hemispheres independent when corpus callosum is cut 
  • Still continue with day to day life when corpus callosum cut 
  • Found lateralisation of function