hemispheric lateralisation

• what is the brain divided into?

  • 2 hemispheres
• what is hemispheric lateralisation?

  • form of localisation
  • 2 hemispheres have different specialisation
• function of left hemisphere?

  • language processing
  • logical reasoning
• function of right hemisphere?

  • spatial reasoning
  • facial recognition
  • visual motor tasks
• background to sperrys study 1968

  • 11 people who had undergone treatment for epilepsy
  • commissurotomy - cut corpus callosum
  • 2 hemispheres no longer connected & unable to communicate with each other
  • allowed sperry to see if 2 hemispheres were specialised for certain functions & whether they perform tasks independently
• sperry method 1968

  split brain patients shown pictures/word to right/left visual field & asked to do task

  • describe what you see - images shown to different vf & had to describe what they saw
  • tactile - felt an object in either left/right hand 1) describe verbally what they were touching b) identify similar object from selection
  • draw it - images shown to different vf & had to draw what they had seen
• what does the left hemisphere control?

  • right side of body
• what des the right hemisphere control?

  • left side of body
• is the brain contralateral?

  yes
• results for describe what you see left hemisphere?

  • patient could describe what they saw
  • shows superiority of left for language production
• results for describe what you see right hemisphere?

  • patient could not describe what was shown
  • often report there was nothing present
• results for tactile describe left hemisphere?

  • could describe verbally what they felt
• results for tactile describe right hemisphere?

  • could not describe what they felt & would make wild guesses
• results for identify left hemisphere?

  • could identify by selecting similar appropriate object from series of alternate objects
• results for identify right hemisphere?

  • could identify object by selecting similar appropriate object from series of alternate objects
• results for drawing left hemisphere?

  • right hand drew unclear picture
  • shows superiority of right hemisphere for visual motor tasks
• results for drawing right hemisphere?

  • left hand drew clearer & better pictures even when all p were right handed
  • shows superiority of right hemisphere for visual motor tasks
• * evidence to support from peterson?

  • used brain scans to show wernickes area was active during listening task & brocas was active during reading task
  • both lateralised in left hemisphere.
  • empirical evidence for language centres being localised in left
  • particularly brocas & wernickes which validates his findings
• 3 X of lateralisation?

  1. contradictory evidence from danelli
  2. small sample size
  3. individual differences
• X contradictory evidence from danelli?

  • case study of e.b who had left hemisphere removed at 3
  • made full recovery by 15 & language good as his peers
  • language not strictly lateralised to left.
  • right hemisphere able to recover language function
  • language is not strictly lateralised to left hs
  • sperry findings do not occur in every individual
• X small sample size?

  • only used 11
  • rare & unusual surgery so not alot of available patients
  • surgery no longer done so access to these people is unlikely
  • population
  • ungeneralisable to rest of population
  • all patients had epilepsy so brains different to general population
  • cannot trust that all brains are localised in same way
• X individual differences

  • sperry found some patients experienced more disconnection of 2 hemispheres - lack of control
  • some p able to do tasks better than others as hemispheres slightly connected.
  • he ignored individual differences/ did not investigate fully
  • affected how lateralised different brains appeared
• how are the right & left hemispheres connected?

  • by the corpus callosum