HEMISPHERIC LATERALISATION

• Hemispheric lateralisation - the theory that the two halves of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere
• What are the evaluation points for hemispheric lateralisation?

  Strength - research showing that the hemispheres process different information ( Fink et al )

  Weakness - the idea that the left hemisphere is the analyser and the right hemisphere is the synthesiser may be wrong ( Nielsen et al )
• EVALUATION OF HL - RESEARCH SHOWING THAT THE HEMISPHERES PROCESS DIFFERENT INFORMATION

  A strength of hemispheric lateralisation is that there is research showing that the hemispheres process different information. Fink et al used PET scans to identify which brain areas were active during a visual processing task. When participants were asked to look at a whole image, areas of the right hemisphere were more active. When asked to focus on the finer detail , areas of the left hemisphere were more active. This suggests that hemispheric lateralisation is a feature of the brain.
• EVALUATION OF HL - WEAKNESS (part 1)

  A weakness of hemispheric lateralisation is that the idea that the left hemisphere is an analyser and right hemisphere is a synthesiser may be wrong. There may be different functions in the right hemisphere and left hemisphere, but research suggests people do not have a dominant side of their brain which creates a different personality.
• EVALUATION OF HEMISPHERIC LATERALISATION - WEAKNESS ( part 2 )

  Nielsen et al analysed brain scans from over 1000 people and did find that people used certain hemispheres for certain tasks, but there was no evidence of a dominant side. This challenges a central part of the theory , therefore hemispheric lateralisation has low validity.
• Split brain research uses patients who had experienced a surgical separation of the hemispheres to reduce epilepsy
• What are the evaluation points for Sperry’s split brain research?

  Strength - supporting evidence ( Gazzaniga )

  Weakness - causal relationships are hard to establish
• EVALUATION OF SPERRY’S RESEARCH - STRENGTH

  A strength of Sperry’s research is that there is support from more recent split - brain research. Gazzaniga showed that split - brain participants actually perform better than normal participants on certain tasks , such as they were faster at identifying the odd one out in an array of similar objects. In the normal brain, the left hemisphere's better cognitive strategies are weakened by the inferior right hemisphere. This supports Sperry's findings that the left hemisphere and right hemisphere are distinct.
• EVALUATION OF SPERRY’S RESEARCH WEAKNESS

  A weakness of Sperry's research is that causal relationships are hard to establish. The behaviour of Sperry's split - brain participants was compared to a neurotypical control group. However, none of the participants in the control group had epilepsy, this is a major confounding variable. Any differences that were observed between the two groups may be the result of the epilepsy rather than the split brain. Therefore Sperry’s study has low validity due to the presence of confounding variables.