Hemispheric lateralisation and split-brain research Flashcards
What is hemispheric lateralisation?
Hemispheric lateralisation
There are two halves (or hemispheres) to the brain
Where are the language centres located?
Hemispheric lateralisation
Broca’s area - left frontal lobe
Wernicke’s area - left temporal lobe
Therefore language is lateralised - RH can only form rudimentay words and phrases but adds emotional context to what is being said
RH - synthesiser
LH - analyser
Which functions are not lateralised?
Hemispheric lateralisation
Vision, motor and somatosensory areas
The motor area is contralaterally wired - RH controls movement on left side and LH on right side
Vision
Hemispheric lateralisation
Both contralateral and ipsilateral
Each eye recieves light from LVF and RVF
LVF of both eyes is connected to RH and RVF of bothe eyes to LH
Enables visual areas to comapre slightly diff perspectives from each eye and aids depth perception
Lateralisation in the connected brain
Hemispheric lateralisation
Strength
Fink et al (1996) PET scans indentify which brain areas were active in visual processing task
When ppts with conn brains attended to global elements of an image regions of RH were more active
When required to focus on finner detail, specific areas of LH tended to dominate
Suggests that hemispheric lateralisation is a feature of conn brain as well as s-b
One brain
Hemispheric lateralisation
Limitation
May be diff functions in RH and LH but research suggest people don’t have dom side of brain.
Nielsen et al (2013) analysed brian scans from over 1000 people aged 7-29. Found people used certain hemis for certain tasks - ev for lateral
No ev of a dom side
Suggests notion of right- or left- brained people is wrong
Lateralisation vs Plasticity
Hemispheric lateralisation
Lateralisation is adaptive - enables two tasks to be performed simultaneously with greater efficiency. Rogers et al (2004) showed lateralised chickens could find food while watching for predators but norm chicks couldn’t
On other hand, neural plasticity could also be seen as adaptive. Following damage through illness or trauma, some functions can be taken over by non-specialised areas in oppo hemi. E.g. language function can literally switch sides (Holland et al 1996)
What are split-brain surgeries used for?
Split-brain research
To reduce epilepsy
During a seizure the brain experiences excessive activity which travels from one hemi to the other
Sperry’s procedure
Split-brain research
Sperry (1968) studied how two sep hemis dead with speech and vis
Procedure: 11 ppts who has s-b operation were studied. An image prohected into ppts RVF and same or diff image to LVF.
Presenting image to one hemi in a s-b ppt meant info cannot be conveyed between hemispheres
Sperry’s findings
Split-brain research
When object was shown to ppts RVF (linked to LH), ppt could describe what was seen
They couldn’t do this when object shown to LVF (RH)
This is because, in connected brain, messages from RH are relayed to language centres in LH - not possible in S-B
Ppts could still select matching object out of sight using left hand when object projected into LVF
Same for closely associated objects
A picture shown to LVF could still elicit an emotional response but ppts would still report seeing nothing
These observations show how certain functions are lateralised in the brain & support view that LH is verbal & RH is ‘silent’ but emotional
Evaluation: Reseach Support
Split-brain research
Strength - Support from more recent S-B research
Gazzaniga (Luck et al (1989) showed that S-B ppts perform better than connected controls on certain tasks
E.g. faster at identifying odd one out in array of similar objects than normal controls
In normal brain, LH’s better cog stats are ‘watered down’ by inferior RH (Kingstone et al 1995)
There4, supports Sperry’s earlier findings that ‘left brain’ and ‘right brain’ are distinct
Evaluation: Generalisation issues
Split-brain research
Limit - causal relationships are hard to establish
Behaviour of Sperry’s S-B ppts was comapred to neurotypical CG
Issue is none of ppts in CG had epilepsy - major confounding variable
Any differences observed between the 2 groups may be result of epilepsy rather than S-B
There4, some unique features of S-B ppts’ cog abilities may have been due to their epilepsy
