Hemispheric Lateralisation Flashcards
hemispheric lateralisation
assumption that the two hemispheres of the brain are functionally different
certain mental processes are controlled by the left hemisphere (eg language) and some by the right hemisphere (eg spatial awareness)
who did split brain research
Sperry (1967)
Sperry (1967)
used a unique gc of 11 ppts, all of whom had undergone the same surgical treatment for there severe epilepsy which involved cutting the corpus collision and other tissues which connect the two hemispheres
procedure
Focus on dot in centre of screen (fixation point)
Project image or word to patients right visual field (processed by LH) or left visual field (processed by RH)
followed by a task
what were the tasks
- describing what you see
- recognition by touch
- composite words
- describing what you see - findings
picture of object projected to RVF, could easily describe what was seen.
same object shown to LVF, couldn’t describe and reported nothing there.
this is because for most people language is processed in the left hemisphere
therefore, when shown to the LVF it was processed by the RH which has a lack of language centres to be able to describe it
in ‘normal’ brains, the corpus collosum would allow the two hemispheres to communicate this information
- recognition by touch - findings
although ppts unable to attach verbal labels to objects projected to their LVF, they could select a matching object from a grab-bag of different objects using their left hand (controlled by RH)
objects were placed behind a screen so couldn’t be seen.
left hand also able to select the most closely associated object (eg ashtray selected in response to a cigarette)
not able to verbally identify what they had seen but could ‘understand’ what the object was using the RH and selecting the corresponding object
- composite words - findings
if two words were presented simultaneously, one on either side of the visual field (eg. ‘face’ on the left and ‘key’ on the right), the patient would say the word ‘key’ but write with their left hand the word ‘face’ or draw a face with their left hand
this shows the superiority of left hemisphere (Broca’s area) for language and speech production, and the superiority of the right hemisphere for drawing
conclusion
the research suggests that the brain is specialised in its function with regards to specific areas of each hemisphere.
eg, language is processed by/localised in the left hemisphere
Evaluate: research into hemispheric lateralisation/split-brain research
- STRENGTHS
P) highly controlled
E) methodology praised for using highly standardised procedures conducted in a controlled environment to control EVs
E) eg one eye covered to ensure only one VF was visible, images flashed for 1/10th second so couldn’t spread to VF/both sides of the brain
L) high internal validity
Evaluate: research into hemispheric lateralisation/split-brain research
- LIMITATIONS
P) flawed research evidence
E) unusual and limited sample of ppl not well matched to a control group
E) 11 split brain ppts had received drug therapy for different times for their severe epilepsy. some experienced more disconnection of hemispheres from their surgery. control gc had no history of epilepsy.
L) reduced validity, brings conclusions into doubt
P) oversimplifies and overemphasises distinction between LH and RH
E) although verbal and nonverbal labels can be usefully applied to summarise the differences between the hemispheres, modern neuroscientists would say the distinction is less clear cut and more messy
L) reductionist, more holistic/more research needed
P) evidence against from case studies which show language may not be restricted to LH
E) Gazzaniga (1998) reported on case of JW
E) developed ability to speak out of RH and can now speak about info presented to left or right H
L) disconfirms the conclusion that RH cannot handle language
E) evidence against from brain plasticity
P) lateralisation further complicated by age
E) lateralisation of function may change throughout an individuals lifetime
E) Szflarski (2006); language became more lateralised to the LH as children developed into adolescents but after 25 lateralisation decreases
L) more complex process than many realise/than research suggests
P) differences in function may be overstated
E) SBR given rise to the belief that there are clear cut distinctions between LH and RH
E) BUT modern neuroscientists argue the distinction is less clear cut because the hemispheres are in constant communication with one another for every day tasks, and many behaviours associated with one can be effectively performed by the other
L) more research needed to fully understand it
