Hemispheric lateralisation

• What is hemispheric lateralisation?

  The division of functions between the left and right hemispheres of the brain.
• What does the right hemisphere do?


  Provides emotional context to what is said or heard. It is the synthesiser
• What are the right hemisphere and the left hemisphere responsible for?


  RH = the synthesiser

  LH = the analyser
• What functions are not lateralised?


  Vision and motor skills
• What is contralateral wiring?

  Right hemisphere controls certain functions on the left side of the body and the left hemisphere controls certain functions on the right side of the body
• What is vision?

  Vision is a contralateral and ipsilateral function (opposite and same side of the brain is used) where each eye receives light from the left vision field and the right vision field
• How does vision in both fields help?


  It helps to add depth perception and perspective
• What are the evaluation points for lateralisation?

  1. Lateralisation in connected brain:

  • Fink et al 1996 looked at PET scans and gave evidence that hemispheres process information differently
  • RH is more active when looking at the bigger picture
  • LH is more active when focussing on finer details

  1. 2. No dominant side in the brain:

  • Different functions in the left and right hemisphere but people do not have a dominant side
  • Nielsen et al 2013 looked at over 1000 brain scans of people (7-29 years old) and found that people used different hemispheres for certain tasks
• What was the aim of Sperry and Gazzaniga (1967)


  Investigate the extent to which the 2 hemispheres are specialised for certain functions - first to investigate hemispheric lateralisation
• What was the method used for the visual field experiment?


  1. Image was projected to patient's left visual field (LVF) (processed by the RH) or the RVF (processed by the LH)
  2. When information is presented to one hemisphere in a split-brain patient, information is not transferred to the other hemisphere as the corpus callosum is cut
  3. To isolate the visual field, one eye was blindfolded and pps were asked to fixate at a certain spot on the screen
• What were the different tests conducted by Sperry and Gazzaniga? (1/2)


  • DESCRIBE what you see - picture is presented and pps had to describe what they saw
  • TACTILE test - object is placed in left/right hand and pps had to describe the object OR pick a similar object from a choice of alternate objects
  • COMPOSITE WORDS task - 2 words were shown on either side of the visual field (e.g. 'key' on the left and 'ring' on the right)
• What were the different tests conducted by Sperry and Gazzaniga? (2/2) 


  • DRAWING task - pps were shown a picture in either their LVF or RVF and had to draw what they saw
  • MATCHING FACE task - pps were asked to match a merged face to the originals from a series of other faces

  The image was flashed up in one hemisphere at 1/10 of a second - the eyes have no chance of moving so only one visual field is used
• What should have been found in the 'normal brain'?

  Corpus callosum shares the information between the hemispheres to form a complete picture of the visual word|
• What should be found in the split-brain?


  Information is not shared between the hemisphere because each is seen as a separate brain
• What were the findings of the visual test?

  • VISUAL - picture was shown to RVF and language was used so the picture could be described (in normal brain the RH sends the message to the lang centre in the LH)
  • Picture shown to LVF = pps could not describe what was seen - "Nothing was there"
• What were the results of the tactile test?


  • The object in the LVF could not attach verbal description but could select objects from a bag (behind a screen) with the left hand
  • Shows that the motor movements occur in the right hemisphere
• What were the composite words test results?


  • Patient writes 'key' with left hand but say the word 'ring'
  • LVF sees the word 'key' (processed by RH) so left hand can write the word as RH = motor movements
  • RVF sees the word 'ring' (processed by LH) so the word is said because LH = language centre
• What were the results of matching faces test?


  • The RH is dominant for facial recognition so the picture from the LVF was consistently selected whilst the picture in the RVF was ignored