Hemispherical Lateralisation and Split-Brain Research

• Localisation


  The theory that specific areas of the brain are associated with particular physical and psychological functions
• Lateralised


  Localised on one or the other side of the brain

  
• Hemispheres of the brain

  The human brain is divided into two halves called the left and right hemispheres

  
• Hemispheric lateralisation


  The idea that the two halves of the brain are functionally different, and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other.
• Strength of hemispheric lateralisation

  Lateralisation in the connected brain

  - Fink et al used PET scans to identify which brain areas were active during a visual processing task.

  - When participants with connected brains were asked to attend to global elements of an image (such as looking at a picture of a whole forest) regions of the RH were much more active.

  - When required to focus on the inner detail (such as individual trees) the specific areas of the LH tended to dominate.

  - This suggests that, at least as far as visual processing is concerned, hemispheric lateralisation is a future of the connected brain as well as the split-brain.
• Limitation of hemispheric lateralisation

  One brain

  - Nielsen et al (2013) analysed brain scans from over 1000 people aged 7 to 29 years and found that people used certain hemispheres for certain tasks (evidence for lateralisation).

  - But there was no evidence of a dominant side i.e. not artist's brain or mathematician's brain.
• Split-brain research


  Surgical cutting of the corpus callosum to study the effects of disconnecting the right and left-brain hemispheres - specifically, the independent functioning of the two hemispheres.
• Sperry's research procedure


  - 11 pts who had split brain research were assessed against a control group.

  - Participants covered one eye and looked at a fixed point on a screen.

  - Pictures were flashed onto the right or the left of the screen at high speeds
• Sperry's research findings

  Pictures shown on the right of the screen (to the left visual field) were unable to be descriptively described by the split-brain research patients, due to an inability to convert to language.

  
• Strength of split-brain research

  Research support

  - Luck et al (1989) Split-brained participants are twice as fast at identifying things in the visual field. This supports lateralisation as each side works independently.

  - Kingstone et al (1995) In the normal brain, inferior sides water down performance in side-specific tasks. This supports the idea that separate tasks are carried out by each side
• Limitation of split-brain research

  Generalisation issues

  - Compared to a neurotypical control group.

  - This is a major confounding variable.