Sperry (1968)

Sperry (1968)

1. Key Terms

   • Corpus Callosum
     • The bundle of nerve fibres that connects the two hemisphere of the brain
   • Quasi-experiment
     • The IV in the experiment is not manipulated, it varies naturally

2. Aim

   • Attempts to study the functions of separated and independent hemispheres

3. Procedure

   • 11 ps who had already has surgery on their corpus callosum
     • Sperry did not conduct the surgery, and the surgery was not for the purpose of the study
   • Special apparatus that allowed info. to be presented to one hemisphere was used
   • Ps vision is divided into left and right visual feilds
   • Their hands were hidden from their vision
   • One eye was covered
   • They centered their gaze on a designated fixation point
   • Words or images were flashed onto a screen for 1/10 of a second or less
   • Info. from the left visual field goes to the right hemisphere and vice versa
     • By flashing the image/word to either the lef or right of the fixation point the experimenter determines which hemisphere receives the info.
   • For physical tasks the objects were placed into the ps hands on the other side of a screen out of view
     • The sensory info. is received by only the corresponding hemisphere
       • E.g. left hand goes to right hemisphere
     • The ps were asked to find the same object in a grab bag with either the same or a different hand.

4. Findings

   • Ps act as if they have two minds in one body
   • If a piece of info is sent seen by the left visual field and goes to the right hemisphere, it is only reconised again if it is seen by the same visual feild
   • Visual material shown to the right visual field sent to the left hemisphere can be described in speech and writing
     • If the same material is then shown to LVF, the ps insists they do not see anything. BUT, when asked to pick the object within a group of objects they are able to select the correct one
   • If a different figure was flashed to each hemisphere
     • Eg. a $ to the LVF and a ? to the RVF
     • The ps is asked to draw with their left hand what they have seen, they will draw they saw in the LVF ($)
       • But if you asked them to tell you what they saw they would say the object from the RVF (?)
   • Objects in the right hand, sent to the left hemisphere can be described and named
   • The right hemisphere is able to:
     • Select similar items to a target item
       • E.g. a watch rather than a clock
     • Perform simple arithmetic operations
     • Understand both written and spoken words
     • Identify objects
     • Understand fairly complex instructions
     • Show appropriate emotional reactions

5. Strengths

   • Quasi-experiment allows researchers to investigate variables that are not able to be investigated in a strict laboratory experiment
   • The techniques Sperry developed allowed the functions of the two hemispheres to be studied which previously had been impossible

6. Weaknesses

   • The experiment was a quasi-experiment
     • This does not give the experimenter complete control over the independent variable