HEMISPHERIC LATERAL., LANGUAGE CENTRES, SPLIT BRAIN RESEARCH

• WHAT IS HEMISPHERIC LATERALISATION?

  difference in functions of right and left hemisphere
• DIVISIONS OF THE BRAIN?

  Two hemispheres

  Four lobes (F -> P -

  \

  O

  /

  T )
• HOW IS LANGUAGE LATERALISED?

  left hemisphere
• RESEARCH APPLYING TO LANGUAGE LATERALISATION?

  BROCA

  • language production
  • left frontal lobe (near motor cortex)
  • demonstrated if patients may
  • short sentences of meaningful speech
  • struggle with 'it' or 'the'

  WERNICKE

  • interpreting language
  • left temporal lobe (near auditory cortex)
  • demonstrated if patients may
  • speak fluently
  • speech doesn't even make sense
  • struggle understanding speech of others
• DISCUSSION OF LOCALISATION OF LANGUAGE FUNCTIONS?

  FLINKER ET AL

  • speech production includes not just BA
  • in word production tasks, word shown in sensory areas before PFC (BA links representation to motor cortex)
  • BA facilitates production but not solely responsible for it

  SCHWARZ

  • damage to BA disrupts comprehension (comprehension not localised to WA alone)
  • participants select correct image ('dancer applauds clown/ clown applauds dancer')
  • Broca's aphasia patients correct 62%, neurotypical 100%
  • damage to BA affect some areas of speech comprehension
• RESEARCH DETAILS REGARDING LATERALISATION OF MOVEMENT, VISION AND AUDITORY?

  SPERRY

  RESEARCH METHOD: natural experiment

  DESIGN: independent groups

  SAMPLE: 11 men, right-handed with epilepsy unable to be treated by drugs

  IV: hemispheric disconnection or not

  DV: language and motor performance on visual or tactile tasks
• SPERRY'S PROCEDURE?

  STAGE 1 - VISUAL TASK FOR LANGUAGE ABILITY

  • blindfold one eye
  • stimulus word shown on screen (0.01s)
  • asked to say what saw

  STAGE 2 - TACTILE TASK FOR MOTOR ABILITY

  • blindfold one eye
  • stimulus word shown on screen (0.01s)
  • one hand behind screen and pick object seen

  STAGE 3 - TACTILE TASK FOR LANGUAGE ABILITY

  • place hands under screen
  • object placed in one hand
  • asked to name object
• FINDINGS OF SPERRY'S RESEARCH?

  • participants able to name word/ select object if presented to right visual field/ hand but not if to left visual field
  • participants only able to pick up object with left hand if displayed to left visual field and vice versa
• CONCLUSION OF SPERRY'S RESEARCH?

  • left hemisphere dominant for language
  • each hemisphere controls movement, sensation and vision on the opposite side of the body
• RESEARCH FOR LATERALISATION OF LANGUAGE?

  SZAFLARKI ET AL

  • language becomes more lateralised to left hemisphere initially through childhood and adolesence
  • after age 25, lateralisation decreases each decade
  • cannot make generalisations about lateralisation without considering age
• DISCUSSION FOR SPERRY'S SPLIT BRAIN RESEARCH?

  -individual differences

  -invalid comparison groups

  -artificial data

  + real world application
• INDIVIDUAL DIFFERENCES?

  • some participants experienced drug therapy longer
  • disconnection between hemispheres greater in some than others
  • very small samples
  • lacks validity (performance on task may be affected by variables)
  • results not generalisable
• INVALID COMPARISON GROUPS?

  • control groups contained people with no history of epileptic seizures
  • cannot establish cause and effect
• ARTIFICIAL DATA?

  • in real life situations
  • severed corpus callosum can be compensated for by unrestricted use of two eyes
  • data produced in experimental setting
• REAL WORLD APPLICATION?

  • split brain research
  • helped develop effective therapy for stroke patients
  • aid recovery of stroke patients
  • due to knowledge and expectations of difficulties
  • development of understanding of hemispheric lateralisation
• DIFFERENCE BETWEEN LATERAL AND LOCAL?

  LATERAL: connected to one side

  LOCAL: connected to one specific region