Hemispheric lateralisation and split brain research

• Split brain research (Sperry)

  Procedure: Eleven people who had a split brain operation were studied using a special set up in which an image could be projected to a participants RVF(processed by the LH) and it could be projected to their LVF (processed in their RH). In the normal brain the corpus callsoum would immediately share this information between both hemispheres. However presenting the image to one hemisphere of a split brain participant meant that information cannot be conveyed from that hemisphere to the other.
• Split brain research(Sperry)


  Findings: When the image was shown to a participants RVF, they could describe what they had seen. But they couldn't do this if it was shown to the left. This is because in the connected brain, messages from the RH are relayed to the language centres in the LH, but this isn't possible in split brains. Although they couldn't give verbal labels if the image was projected in the LVF, they could select an object that was closely associated. Shows how certain functions are lateralised.
• Research support - Split Brain

  Gazzaniga showed that split brain participants actually performed better than connected controls on certain tasks. They were faster at identifying the odd one out in an array of similar objects that normal controls. In the normal brain, the LH's better cognitive strategies are watered down by the inferior RH. This supports Sperry's findings that the left brain and right brain are different.
• Split brain - Generalisation issues

  One limitation 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. AN issue was that none of the participants in the control group had epilepsy. This is a major confounding variable. Any observed differences may have been as a result of the epilepsy rather than the split brain.
• Left and Right Hemispheres

  In the case of language, two main centres are only in the LH. So we can say language is lateralised. The RH can only produce rudimentary words and phrases but contributes emotional context to what is being said. This has led to the suggestion that the LH is the analyser whilst the RH is the synthesiser
• HL-Lateralisation in the connected brain

  One strength is research showing that even in connected brains the two hemispheres process information differently. Fink et al used PET scans to identify which brain areas were active during a visual processing task when participants with a connected brain were asked to attend to global elements of an image regions of the RH were more active. When needing to focus on finer details areas of LH tended to dominate
• HL- One brain


  A limitation is the idea that the LH as an analyser and RH as a synthesiser may be wrong. There may be different functions in the RH and LH, but research suggests people do not have a dominant side of their brain which creates a different personality. Nielsen et al. analysed brain scans from over 1000 people aged 7-29 and found people used certain hemispheres for certain tasks but there was no evidence of a dominant side.