Sperry (1968) split-brain research

• Sperry (1968) Split-brain research: Procedure

  • 'Split-brain' = two hemispheres surgically separated by cutting the connections e.g. the corpus callosum
  • Used to treat severe epilepsy to reduce 'electrical storm' across hemispheres
  • 11 split-brain ppts were studied using a set-up where the image or word is projected to the right visual field (processed by left hemisphere), and the same, or different, image could be projected to the left visual field (processed by right hemisphere)
  • Presenting image to one hemisphere meant that information couldn't be conveyed from that hemisphere to the other
• Sperry (1968): Findings & conclusions

  • Object shown to right visual field:
  • Ppt can describe what is seen (language centres in left hemisphere)
  • Object shown to left visual field
  • Can't name object (no language centres in right hemisphere)
  • Can select matching object behind screen using left hand
  • Can select object closely assoc w/ pic (e.g. ashtray of pic of cigarette)
  • Pinup pic shown to left visual field, ppt giggled but reported seeing nothing
  • Demonstrates how certain functions are lateralized in brain, shows left hemisphere is verbal & the right hemisphere is 'silent' but emotional
• One strength is support from more recent split-brain studies

  • Luck et al (1989) showed that the split-brain ppts are better than normal controls e.g. twice as fast at identifying the odd one out in an array of similar objects
  • In the normal brain, the left hemisphere's superior processing abilities are 'watered down' by the inferior right hemisphere (Kingstone et al 1995)
  • This supports Sperry's earlier findings that the 'left brain' and 'right brain' are distinct in terms of functiions and abilities
• One limitation is that casual relationships are hard to establish

  • In Sperry's research the behavior of the split-brain ppts was compared to a neurotypical control group
  • However, none of the control group had epilepsy. Any differences between the groups may be due to epilepsy not the split-brain (a confounding variable)
  • This means that some of the unique features of the split-brain ppts cognitive abilities might have been due to their epilepsy
• Evaluation extra: Ethics

  • Sperry's ppts were not deliberately harmed and procedures were explained in advance to gain informed consent
  • However, ppts may not have understood they would be tested for many years, and participation was stressful
  • This suggests that there was no deliberate harm but the negative consequences make the study unethical