6. Split-Brain Research Into Hemispheric Lateralisation

• 1. Split-Brain Research Into Hemispheric Lateralisation

  Hemispheric Lateralisation:

  • brain, 2 separate halves; each hemisphere has functional specialisations.
  • e.g. left (speech/language), right (visual motor).
  • hemispheres communicate through corpus callosum (bundle of nerve fibres).
• 1a. Split-Brain Research Into Hemispheric Lateralisation

  Left Brain:

  • language
  • analytical tasks
  • control right side body
  • objects visible in right visual field

  Right Brain:

  • emotional content of language
  • control left side body
  • motor tasks
  • face recognition
  • left visual field
• 2. Split-Brain Research Into Hemispheric Lateralisation

  Split-Brain Research -

  began when surgeons researched treatment for epileptic patients.

  Sperry (1968):

  • quasi exp; 11 participants (epileptics, couldn’t be treated w/ drugs).
  • corpus callosums’ split, communication line between 2 hemispheres removed.
• 2a. Split-Brain Research Into Hemispheric Lateralisation

  Sperry (1968):

  • told to gaze at fixation point; slides put either side of fix. point.
  • image projected into right v.f. (processed by left); projected to left v.f. (processed by right).
  • tactile tasks carried out, w/ hands under screen so couldn’t see - use ’feel’ only.
  • in normal brain, corpus callosum share info between hemispheres; split-brain, info not communicated to other hemisphere.
• 2b. Split-Brain Research Into Hemispheric Lateralisation

  Sperry (1968):

  • pic of object shown to right v.f., described what saw.
  • shown to left v.f., no description + claimed nothing there.
  • language processed in left h., so patients’ inability describe in left v.f. bc lack language centres in right h.
  • normal brain, messages from right h. relayed to language centres in left h.
• 2c. Split-Brain Research Into Hemispheric Lateralisation

  Sperry (1968) - Recognition by Touch:

  • able select matching object using left hand (linked to right hem).
  • left hand also select object closely associated w/ object presented to left v.f.
  • couldn’t verbally identify, but could understand object using right hem.
• 2e. Split-Brain Research Into Hemispheric Lateralisation

  Sperry (1968) - Faces:

  • right hem dominant in facial recognition.
  • asked match face from other faces, pic processed by right hem (in left v.f.) consistently selected.
  • pic presented to left hem ignored.
  • when pic made up of 2 diff face halves presented (1/2 to each hem.), left hem dominated verbal description, right hem dominated selecting matching face.
• Split-Brain Research Into Hemispheric Lateralisation (Evaluation)

  Strength:

  P - Sperry‘s research = impressive findings = value in clinical practice (real-life).

  E - main conclusion; left hem responsible speech/language + right hem responsible visuospatial tasks.

  E - challenges localisation theory, suggests instead of brain having sections for specific tasks, connectivity between 2 hems more likely.

  L - increase understanding in brain process; provides alternative for localisation theory of brain’s functioning.
• Split-Brain Research Into Hemispheric Lateralisation (Evaluation)

  Strength:

  P - research into split-brain use highly specialised + standardised procedures.

  E - Sperry praised for showing visual info to 1 hem at a time; image flashed up for 1/10th of sec = patient no time to move eye across image (prevent spread of info across both v.f.).

  L - ensuring only 1 hem receiving info at time = useful + high controlled procedure = high internal validity + reliability.
• Split-Brain Research Into Hemispheric Lateralisation (Evaluation)

  Limitation:

  P - researchers urge caution in widespread acceptance as split-brain patients constitute unusual sample of people.

  E - only 11 took part - all who had history of epileptic seizures, which some argue caused changes in brain, influencing findings.

  E - control group (11 people w/ no epilepsy) inappropriate as can hardly compare the 2 groups.

  L - findings low ecological validity, sense of lack of generalisability.