Hemispheric lateralisation

• Hemispheric lateralisation: The idea that the two half's of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other
• Split-brain research: A series of studies which began in the 1960s involving people with epilepsy who had experienced separation of the hemispheres of their brain to reduced severity of epilepsy. Enables researchers to test lateral functions of the brain in isolation.
• For most, the LH is the side that manages language. This is because it contains both Broca and Wernicke's area's . This means that language is lateralised. The RH can only produce rudimentary words but contributes emotional context.
• Many functions are not lateralised such as motor areas however they may be cross-wired. This means that the RH controls movement on the left side and the LH controls movement on the right.
• Each eye receives light from the LVF and the RVF. The LVF of both eyes is connected to the RH and the RVF of both eyes is connected to the LH. This allows for the visual fields to compare slightly different perspectives for both eyes.
• Sperry (1968)- Procedure

  • 11 people who had a split-brain operation were studied.
  • An image would be projected to their RVF (processed by LH), and the same or different image would be projected into the persons LVF (processed by RH).
  • In a normal brain they would get the full picture because the sides can talk to each other but due to their brain being split they cannot see the full picture.
• Sperry (1968)- Findings

  • When a picture was shown to their RVF they could describe what was seen but they couldn't do this is the picture was shown to the LVF.
  • Despite this they could select a matching picture using their left hand.
• Sperry (1968)- Conclusions

  • Show how certain functions are lateralised and supports the view that LH is verbal and RH is silent but emotional.
• Lateralisation Evaluation (strength):

  • Research shows that even in connected brains the two sides process things differently.
  • When looking at a full image PET scans showed the RH brain was more active but when looking at finer details the LH was more active.
• Lateralisation Evaluation (limitation):

  • The idea of the LH being an analyser and the RH being a synthesiser may be wrong.
  • There may be different functions but people may not have a dominant side that controls their personality.
  • The notion of right-brained people and left-brained people is wrong.
• Split-brain research Evaluation (strength):

  • Research support.
  • Gazzaniga showed that split brain participants perform better in certain tasks. For example, finding the odd one out.
  • This supports Sperry's findings.
• Split-brain research Evaluation (limitation):

  • There is generalisation issues.
  • The participants had epilepsy which is a confounding variable.
  • It is also hard to replicate so only a small sample size was used.