Sperry

• Lateralisation of function is the belief that the two hemispheres of the brain have different functions: the right is in charge of the left side of the body, movement, object recognition and creative activities. The left side is in charge of the right side of the body, communication and the ability to read and write.
• Contralateral control means that the left hemisphere controls the right side of the body and vice versa. For example, information presented to the left visual field is processed in the right hemisphere.
• Sperry wanted to investigate how the severed corpus callosum (done during a procedure to treat severe epilepsy) impacts communication between the two hemispheres.
• Sperry aimed to record the psychological effects of hemisphere deconnection and to find evidence of lateralization of function in normal brains.
• Sperry studied 11 people (male and female) who had undergone the split brain operation to treat severe epilepsy. They had undergone the surgery at different times - the maximum was 5 years before the study. Sperry used opportunity sampling.
• Considered a quasi experiment as the IV (having a split brain) was not manipulated by the researchers. No control group was needed as the function of the visual fields and hemispheres is already known in connected brains.
• Visual tasks procedure:

  1. Participant (with one eye covered) centred their gaze on a fixed point on a translucent screen.
  2. Visual stimuli were projected using a tachistoscope for 1 tenth of a second (too fast for eye movement).
  3. Everything presented to left side of screen was processed in left visual field and vice versa.
• Tactile task procedure:

  1. Participants could feel objects but could not see them.
  2. Objects were placed in each of of the participants hands.
  3. Information about objects placed in left hand was processed in the right hemisphere and vice versa.
• For the visual tasks, Sperry found:

  • Information shown to left visual field can only be recognised by the left visual field.
  • In formation shown to the right visual field could be described in speech and writing.
  • However, if information was presented to left visual field the participant would say they hadn't seen anything (or just a flash of light) but the left hand could point to a matching object.
  • If different objects were shown simultaneously to both visual fields they could draw the object seen in the left visual field and say the object in the right visual field.
• For the tactile tasks, Sperry found:

  • Objects placed in the right hand could be described in speech or writing.
  • Objects felt by one hand could only be recognised by that same hand.
  • When objects were placed simultaneously in both hands and then placed in a pile, both hands would recognise their own object and ignore the others.
• Sperry concluded that split brain patients appear to have two independent streams of consciousness which supports the idea of lateralisation of function.

  Split brain patients have a lack of communication due to the severed corpus callosum.