Hemisphere deconnection and unity in conscious awareness

1
Sperry (1968)
Hemisphere deconnection and unity in conscious
awareness
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What parts of the brain do what??

• Brain stem (medulla) - controls breathing,
  swallowing, heartbeat
• Cerebellum - controls co-ordination movement
• These are core structures snakes fish have
  them too

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The limbic system

• Fully developed in mammals
• Controls instinctive behaviour
• Stores memories
• Helps mammals be more flexible than other animals

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Cerebral Cortex

• Fully developed only in humans
• Gathers information from all 5 senses
• Complex behaviour thought, memory, language
• Divided into 2 cerebral hemisphers

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The 2 hemispheres

• Brain is bilaterally symmetrical
• 2 hemispheres are mirror images (eg 2 of each
  lobe)
• Connected by nerve fibres CORPUS CALLOSUM

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Seeing Touching

• Right hemisphere controls left hand side of body
• Left hemisphere controls right hand side of body
• Eg left field of vision (LFV) goes to right
  hemisphere (RH)
• Corpus callosum enables hemispheres to share
  information

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Roger Sperry(1913-1994)

• Fechner (1860) proposed that if brain was split
  there would be 2 minds inside the head
• In 1961, surgeons began treating severe epilepsy
  by severing corpus callosum
• In 1981, Roger Sperrry awarded Nobel Prize for
  work with split-brain patients

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The Study

• Review of split brain procedure - behavioural,
  neurological and psychological effects
• Method natural experiment
• Participants 11 commissurotomised patients
• Procedure various experiments
• IV split brain/ intact brain
• DV performance on tasks

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Sperrys apparatus

• Based on Overhead Projector
• Image/word flashes on L or R screen for 1/10th of
  a second
• Too quick for both eyes to focus data goes to
  one hemisphere only
• Can touch but not see objects

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Typical Procedure

• Object flashed to left side of screen
• Then flashed to right side
• P doesn't know he has seen it before
• Each hemisphere has its own memories - separate
  consciousness

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Another Typical Procedure

• Picture projected to Right Visual Field - goes
  to Left Hemisphere -
• P can talk and write about it BUT
• If picture projected to Left Visual Field - goes
  to Right Hemisphere
• P says he saw nothing BUT can pick up object from
  a group with his Left Hand

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Yet Another Typical Procedure

• Two words flashed simultaneously
• LVF RVF
• KEY CASE
• P can say CASE
• P can pick up key with left hand
• BUT can not say KEY or what kind of case - would
  say "in case of fire"

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Conclusions

• In everyday life these patients did not appear to
  have problems e.g. could read, watch TV etc.
• Some ST memory and concentration problems some
  inappropriate emotions planning difficulties
  (see Raine)
• Sperry's work shows - 2 hemispheres are not equal
• People have 2 independent streams of conscious
  awareness each with its own perceptions and
  memories

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Discussion

• Sperry has made a huge contribution to our
  understanding of functional lateralisation
• However Beware of generalising - individual
  differences
• Some people have more lateralised brains than
  others e.g. some people have language in the R
  hemisphere
• Some differences between L and R handers and
  between sexes
• Were P's brains normal before the surgery - can
  we compare - most evidence about brain function
  comes from brain damaged patients!