Hemispheric lateralisation and split-brain research Flashcards
Hemispheric lateralisation
The brain is l____
AO1: Hemispheric lateralisation
‘lateralised’ i.e. 2 sides (hemispheres)
Localised
Some functions are localised and appear in both ____
AO1: Hemispheric lateralisation
‘left and right hemispheres (LH and RH).
e.g. auditory, visual, motor, somatosensory areas’.
Localised and lateralised
2 main language centres are in the LH (for most people) - Broca’s area (left frontal lobe), Wernicke’s area (left temporal lobe).
What does the RH provide?
AO1: Hemispheric lateralisation
RH produces rudimentary words but provide emotional context. LH may be the analyser, RH the synthesiser.
Contralateral
What is contralateralisation?
AO1: Hemispheric lateralisation
In the motor area, the RH controls the left side of the body and vice versa (cross-wired).
Contralateral and ipsilateral
Left visual field (LVF) of both eyes is connected to the RH and right visual field (RVF) of both eyes is connected to the LH.
This enables the visual areas what?
AO1: Hemispheric lateralisation
Enables the visual areas to compare the slightly different perspectives to from each eye and aids depth perception.
Same arrangement for auditory areas.
Procedure;
Eleven split-brain participants were studied.
‘Split-brain’ = two hemispheres surgically separated by cutting the connections e.g. the corpus callosum.
Why was this surgery taken?
A01: Sperry (1968) Split-brain research
Used to treat severe epilepsy to reduce the ‘electrical storm’ across hemispheres.
Procedure;
Image or word projected to RVF (processed by LH), and same, or different, image could be projected to the LVF (processed by RH).
What does this mean?
A01: Sperry (1968) Split-brain research
Presenting the image to one hemisphere meant that the information could not be conveyed from that hemisphere to the other.
Findings and conclusions;
Object shown to RVF:
A01: Sperry (1968) Split-brain research
- Participant can describe what is seen (language centres in LH).
Findings and conclusions;
Object shown to LVF:
* Cannot ____
* Can select ____
* Can select object ____
* Pinup picture shown to LVF, participant giggled but reported seeing nothing.
A01: Sperry (1968) Split-brain research
‘name object (no language centres in RH)’.
‘matching object behind screen using left hand’.
‘closely associated with picture (e.g. ashtray if picture of cigarette)’.
Demonstrates how certain functions are lateralised in the brain, shows that LH is verbal and the RH is ‘silent’ but emotional.
1 strength is evidence of lateralised brain functions in normal brains.
PET scans show when ‘normal’ participants attend to global elements of an image, the RH is more active.
What did they find when they were required to focus on finer detail?
Suggesting?
When required to focus on finer detail the specific areas of the LH tend to dominate (Fink et al. 1996).
This suggests that hemispheric lateralisation is a feature of the normal brain as well as the split-brain.
1 limitation is the idea of analyser vs. synthesiser brain may be wrong.
There may be different functions in the RH and LH but research suggests people do not have a dominat side, creating a different personality.
What did Nielsen et al. find?
What does this suggest?
Nielsen et al. (2013) analysed 1000 brain scans finding people did use certain hemispheres for certain tasks but no dominance.
This suggests that the notion of the right- or left- brained people is wrong (e.g. ‘artist’ brain).
1 strength is support from more recent split-brain studies.
Luck et al. showed that split-brain participants are better than normal controls, e.g. twice as fast identifying the odd one out in an array of similar objects.
What did Kingstone et al. claim?
What does this support?
In the normal brain, the LH’s superior processing abilities are ‘watered’ down by the inferior RH (Kingstone et al. 1995).
This supports Sperry’s earlier findings that the ‘left brain’ and ‘right brain’ are distinct in terms of functions and abilities.
1 limitation is that casual relationships are hard to establish.
In Sperry’s research the behaviour of the split-brain participants was compared to a neurotypical control group.
However, none of the control group had epilepsy.
What does this mean?
Any difference between the groups may be due to epilepsy not the split-brain (confounding variable).
This means that some of the unique features of the split-brain participants’ cognitive abilities might have been due to their epilepsy.
Ethics.
Sperry’s participants were not deliberately harmed and procedures were explained in advance to gain informed consent.
However, what may have they not understood?
They may not have understood they would be tested for many years, and participation was stressful.
This suggests that there was no deliberate harm but the negative consequences make the study unethical.
