HEMISPHERIC LATERALISATION Flashcards
Hemispheric lateralisation
The brain is lateralised ie. two sides (hemispheres)
Localised
> Some functions are localised and appear in both left and right hemispheres (LH and RH)
eg. auditory, visual, motor, somatosensory areas
Localised and Lateralised
> Two main language centres are in the LH (for most people) - Broca’s area is (left frontal lobe), Wernicke’s area (left temporal lobe)
RH produces rudimentary words but provides emotional context. LH may be the analyser, RH the synthesiser
Contralateral
> In the motor area, the right hemisphere controls the left side of the body and vice versa (cross-wired)
Contralateral and Ipsalateral
> 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.
Enables the visual areas to compare the slightly different perspective from each eye and aids depth perception.
Same arrangement for auditory areas.
Sperry’s (1968) Split-Brain Research Procedure
> ‘Split-brain’ = two hemispheres surgically separated by cutting the connections eg. the corpus callosum
Used to treat severe epilepsy to reduce the ‘electrical storm’ across hemispheres
11 split-brain pt’s were studied using the set-up shown on the left. Image or word projected to RVF (processed by LH), and same, or different, image could be projected to the LVF (processed by RH)
Presenting the image to one hemisphere meant that the information could not be conveyed from that hemisphere to the other.
Sperry’s (1968) Split-brain Research Findings
> Object shown to RVF - participant can describe what is seen (language centres in LH).
Object shown to LVF - cannot name object (no language centres in RH), can select matching object behind screen using left hand, can select object closely associated with picture (eg. ashtray if picture of cigarette), Pinup picture shown to LVF, participant giggled but reported seeing nothing.
Demonstrates how certain functions are lateralised in the brain, shows that LH is verbal and the RH is ‘silent’ but emotional
Evaluation points: Split-brain research
> Support from more recent split-brain studies
Casual relationships are hard to establish
Ethics
PEEL IT: Split-brain research, recent split-brain studies
P-One strength is support from more recent split-brain studies.
E-Luck et al showed that split-brain participants are better than normal controls eg. twice as fast as identifying the odd one out in an array of similar objects.
E-In the normal brain, the LH’s superior processing abilities are ‘watered down’ by the inferior right hemisphere (Kingstone et al. 1995)
L-This supports Sperry’s earlier findings that the ‘left brain’ and the ‘right brain’ are distinct in terms of functions and abilities
PEEL IT: Split brain research, casual relationships
P-One limitation is that casual relationships are hard to establish
E-In Sperry’s research the behaviour of the split-brain participants was compared to a neurotypical control group.
E-However, none of the control group had epilepsy. Any differences between the groups may be due to epilepsy not the split-brain (a confounding variable)
L-This means that some of the unique features of the split-brain participants’ cognitive abilities might have been due to their epilepsy.
PEEL IT: Split-brain research, ethics
P-An issue with Sperry’s split brain research is ethics.
E-Sperry’s participants were not deliberately harmed and procedures were explained in advance to gain informed consent.
E-However, participants may not have understood they would be tested for many years, and participation was stressful
L-This suggests that there was no deliberate harm but the negative consequences make the study unethical.
Evaluation Points: Hemispheric Laterlisation
> Evidence of lateralised brain functions in ‘normal’ brains
Idea of analyser vs synthesiser brain may be wrong
Lateralisation vs plasticity
PEEL IT: Hemispheric lateralisation, evidence in ‘normal’ brains
P- A strength is evidence of lateralised brain functions in ‘normal’ brains
E- PET scans show when ‘normal’ participants attend to global elements of an image, the RH is more active
E-When required to focus on finer detail, the specific areas of the LH tend to dominate.
L- This suggests that hemispheric lateralisation is a feature of the normal brain as well as the split-brain.
PEEL IT: Hemispheric Lateralisation, Idea of analyser vs synthesiser
P-One limitation is the idea of analyser versus synthesiser may be wrong
E-There may be different functions in the RH and LH but research suggests people do not have a dominant side, creating a different personality.
E-Nielsen et al (2013) analysed 1000 brain scans, finding people did use certain hemispheres for certain tasks but no dominance
L- This suggests that the notion of right- or left-brained people is wrong (eg. artist brain).
PEEL IT: Hemispheric Lateralisation, Lateralisation versus Plasticity
P- An issue is knowing whether something is due to lateralisation or plasticity.
E-Lateralisation is adaptive, enabling two simultaneous tasks with greater efficiency, eg. research found only lateralised chickens better at finding food while watching for predators.
E-On the other hand, neural plasticity is also adaptive. After damage to brain, language function can ‘switch sides’
L-This seems to suggest that lateralisation is first preference but ultimately plasticity is more important because it deals with loss of lateralisation
