hemispheric lateralisation

Question 1

hemispheric lateralisation

Answer 1

idea that two halves (hemispheres) of the brain are functionally different and certain mental processes/behaviours are controlled (specialised to) by one hemisphere rather than the other (have functional specialisations)

Question 2

functions of the left hemisphere

Answer 2

• understanding written/spoken language (Wernicke’s area)
• right visual field
• control of right hand
• speech (Broca’s area)
• logical thinking and analytical tasks

Question 3

functions of the right hemisphere

Answer 3

• left visual field
• spatial awareness
• musical ability
• creativity
• recognising faces
• control of left hand
• emotional content of language
• drawing

Question 4

corpus callosum

Answer 4

• thick bundle of nerves connecting the 2 hemispheres
• as 2 hemispheres dont work in isolation
• allows them to communicate so whole brain works as one complete organ to control behaviour in the whole body

Question 5

Sperry and Gazzaniga overview

Answer 5

• studied 11 individuals who underwent surgical procedure where corpus callosum was cut to control frequent and severe epileptic seizures
• control group with no epilepsy history
• tachistoscope is instrument used for exposing objects to eye for very brief measured amount of time
• Sperry presented stimuli e.g. words/pictures to one visual field using it
• participants fixated on dot in centre of screen while stimuli are presented to one half of the visual field briefly (1/10th of a second)
• so participant doesnt have time to move their eyes so that both eyes can see it
• so only goes to one hemisphere and since corpus callosum is cut it cant go to the other one
  so measures functions of each hemisphere

Question 6

Sperry and Gazzaniga 4 tasks in the study

Answer 6

describing what you see
recognition by touch
composite words
matching faces

Question 7

‘describe what you see’

Answer 7

• picture of object was shown to either left or right visual field and participant asked to name the object
• results:
• if object shown to RVF, was named easily as it got sent to left hemisphere responsible for language
• if object shown to LVF patient couldnt describe it and typically reported nothing being there

Question 8

‘recognition by touch’

Answer 8

• objects shown to participants LVF and asked to select a matching or related object from a grab bag of objects using their left hand
• objects were placed behind screen so as to not be seen
  results:
• left hand was able to select a matching /related object (e.g. ashtray when cigarette picture) suggesting right hem is responsible for visuo-spatial skills as they could visually understand it
• but could not describe the object so left hem is responsible for language

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Question 9

‘matching faces’

Answer 9

• participants shown image of face (different ones in each visual field) and asked to match it to one from series of other faces
• also given composite pictures made up of 2 faces (one half presented to each VF)
• results:
• first task: picture processed by right hem LVF was consistently selected whilst picture presented to left hem RVF was consistently ignored
• suggests right hem dominant in processing faces (explain why)
• second task: half presented to left hem dominated the description of the face but half presented to right hem dominated in terms of selecting a matching picture
• suggests facial recognition is lateralised to right hem and language to the left

Question 10

‘composite words’

Answer 10

• 2 words presented simultaneously- one on either side of visual field (e.g. key on left and ring on right)
• participants asked to say what they could see and draw it if they couldnt say it
• results:
• couldnt say the word key but could draw a key with left hand suggesting right hem is responsible for drawing
• could say word ring as it was presented to the right eye and processed by the left hemisphere suggesting left hem is responsible for language

Question 11

conclusions of Sperry and Gazzaniga’s study

Answer 11

• left hem responsible for speech and language and right hem responsible for visuo-spatial processing and facial recognition
• this is evidence for hemispheric lateralisation not localisation of function.

Question 12

visual fields and hemispheres

Answer 12

• anything in the left visual field goes to the right hemisphere
• anything in the right visual field foes to the left hemisphere

Question 13

evaluation points for hemispheric laterlisation

Answer 13

• strength from key contribution
• strength from standardisation and control
• weakness from sample issues and artificial task
• weakness from pop-psych oversimplification

Question 14

strength of hemispheric lateralisation from Sperry and Gazzaniga’s study

Answer 14

• Sperry and Gazzaniga’s work produced an impressive and sizeable body of research findings, the main conclusion of which appears to be that the left hemisphere is more geared towards analytical and verbal tasks, whilst the right is more adept at performing spatial tasks and music
• The right hemisphere can only produce rudimentary words and phrases but contributes emotional and holistic content to language.
• This a key contribution to our understanding of brain processes.

Question 15

strength of hemispheric lateralisation (Sperry and Gazzaniga’s study) from standardisation and control

Answer 15

• Split-brain research used highly specialised and standardised procedures
• Presenting visual information to one hemispheric field at a time was ingenious
• Participants stared at a fixation point while one eye was blindfolded
• Images were flashed for 1/10 of a second
• This prevented information spreading across both visual fields and hemispheres
• Only one hemisphere received information at a time
• The procedure was very useful and well-controlled
• Cause and effect could be determined
• This supports the internal validity of the theory of hemispheric lateralisation

Question 16

weakness of hemispheric lateralisation (Sperry and Gazzaniga’s study) from sample issues and artificial task

Answer 16

• Split-brain patients are an unusual, small sample (only 11 participants)
• All participants had epileptic seizures
• may have caused unique changes in the brain
• Participants differed in hemispheric disconnection and drug therapy
• The control group had no history of epileptic seizures
• The data was artificially produced
• The research lacks internal and external validity
• The theory of hemispheric lateralisation cannot be confidently supported

Question 17

weakness of hemispheric lateralisation (Sperry and Gazzaniga’s study) from pop-psych oversimplification

Answer 17

• Pop-psychological literature overemphasises and oversimplifies hemispheric differences
• Functional distinction is less clear-cut and messier
• The ‘verbal’–‘non-verbal’ distinction is oversimplified
• The two hemispheres are in constant communication
• Behaviours associated with one hemisphere can be performed by the other hemisphere
• Hemispheric lateralisation may be more complex
• The brain may work more holistically
• Split-brain research does not dispel the left-/right-brained oversimplification