A03 - Split Brain Research into Hemispheric Lateralisation

• Evaluation of Split Brain Research into Hemispheric Lateralisation?

  + Sperry was highly influential

  +Evidence in support

  -Weakness in Sperry's Sample

  -Low ecological validity

  -Psychologists disagree

  -Ethics
• Strength of Split brain research into hemispheric lateralisation - Sperry was highly influential


  P: Research by Sperry has been influential in the field of neuroscience.

  E: Not only have the highly standardised procedures allowed for replication of the original study.

  E: But it has also led to advancements in our understanding of consciousness and cognition.

  L: In fact, so groundbreaking was his work that he was awarded a nobel prize in 1981.
• Weakness of SBR - ecological validity?


  P: A further weakness of the study related to ecological validity. The findings of study would be unlikely to be found in a real life situation.

  E: Sperry showed participants stimuli for tenth of second so other eye didn't have time to process image.

  E: In reality person with a severed corpus callosum who had both eyes would be able to compensate for such loss.

  L: So although it's useful for helping us to understand hemispheric deconnection this explanation doesn't help further understanding of how split brain patients function every day. (AgCC)
• Weakness of SBR - Psychologists against Sperry & SBR? - PART 1


  P: Not all psychologists agree with Sperry’s conclusion that there clear lateralisation of function in brain.

  E: E.G; Lashely argues the 2 hemispheres don't function in isolation but form a highly integrated system.
• Weakness of SBR - Psychologists against Sperry & SBR? - PART 2


  E: Argued that higher level tasks involve a mixture of ‘left’ & ‘right’ skills, (e.g. in listening to speech we analyse words & patterns of intonation) thus rather than ‘doing their own thing’ 2 hemispheres work together.

  L: Suggesting Sperry’s conclusions too simplistic and we need to consider the interaction between the 2 hemispheres rather than considering them in isolation.
• Strength of SBR - Evidence in support - PART 1

  P: One strength is evidence of lateralized brain functions in ‘normal’ brains and support from more recent split-brain studies.

  E: PET scans show when ‘normal’ participants attend to global elements of an image, the RH is more active. When required to focus on finer detail the specific areas of the LH tend to dominate (Fink et al. 1996). This suggests that hemispheric lateralisation is a feature of the normal brain as well as the split-brain.
• Strength of SBR - Evidence in support - PART 2

  E: Luck et al (1989) showed split-brain participants are better than normal controls e.g. twice as fast as identifying odd one out in an array of similar objects. In ‘normal’ brain LH’s superior processing abilities are ‘watered down’ by inferior RH (Kingstone et al 1995). This supports Sperry’s earlier findings that the ‘left brain’ and ‘right brain’ are distinct in terms of functions and abilities.

  L: This evidence adds validity to the idea of hemispheric lateralisation and that the hemispheres of the brain have their own function.
• Weakness of SBR - Ethics 


  P: Ethics.

  E: Sperry’s participants were not deliberately harmed and procedures were explained in advance to gain informed consent.

  E: However, participants may not have understood they would be tested for many years, and participation was stressful.

  L: This suggests that there was no deliberate harm but the negative consequences make the study unethical.
• Weakness of SBR - Sperry's sample?- PART 1

  P: Criticism of the procedure was Sperry’s sample. 11 participants is a very small sample.

  E: Added to this we also can’t be sure how long each of participants experienced ineffective drug therapy which could have been affecting findings.

  E: Also causal relationships hard to establish. Control was non epileptic participants with no hemispheric deconnection.
• Weakness of SBR - Sperry's sample? - PART 2


  E: Differences between groups may due to Epilepsy not split-brain (a confounding/extraneous variable). This means that some of the unique features of the split-brain participants’ cognitive abilities might have been due to their epilepsy.

  L: But, Sperry may not had any control over small samples - there may not many split-brain patients available to study but he could have improved research by using control of epileptic patients.