Biopsyhcology- Topic 5

split brain research

What is hemispheric lateralisation?

Hemispheric lateralisation means that some functions are controlled by one hemisphere rather than both while most functions(motor, somatosensory, auditory, visual) are localised in both hemispheres.

Where does language centre and contralateral?

Language centres usually in the left hemispheres, Broca' area(left frontal lobe) and Wernicke's area (left temporal lobe). Th and processes the hemispheres are contralateral; the right hemisphere controls the left side of the body and processes the left visual field, and vice versa.

Sperry's Research PROCEDURE

Sperry conducted split-brain research where Sperry studied 11 epilepsy patients who had their corpus collosum cut(which connects the 2 hemispheres). Information was presented seperately to one hemisphere.

Sperry's FINDINGS

When an object was shown to the right visual field(LH), participants could describe it verbally, but when shown to the left visual field(RH), they couldn't verbally report it but could select a matching or associated object with their left hand. This demonstrates that the left hemisphere is verbal and analytical while the right hemisphere is non-verbal but emotional holistic.

A03 STRENGTH

P- One strength is evidence of lateralised brain functions in ‘normal’ brains.

E- For example, PET scans show when 'normal' participants attend to global elements of an image, the RH is more active. When required to focus on finer detail the specific areas of the LH tend to dominate.

E- This suggests that hemispheric lateralisation is a feature of the normal brain as well as the split-brain.

L- Therefore, this increases the validity of the Sperry's findings as evidence of normal brain and split brain patients both show the same results increasing the theoretical value of the study.

A03 LIMITATION

P- One limitation is the idea of analyser versus synthesiser brain may be wrong.

E- There may be different functions in the RH and LH but research suggests people dont have a dominant side, creating a different personality. For example, Nielsen et al analysed 1000 brain scans, finding people did use certain hemispheres for certain tasks but no dominance.

E- This suggests that the notion of the right or left brained people is wrong.

L- Therefore, this lowers the validity of split-brain research, as it oversimplifies how the hemispheres work and wrongly assumes people have a dominant side.

STRENGTH- OF SPERRY

P- One strength is support from more recent split-brain studies.

E- For example, Luck et al showed that split brain participants are better than normal controls such as being twice as fast at identifying the odd one out in an array of similar objects. In the normal brain, LH's superior processing abilities are 'watered down' by the inferior right hemisphere.

E- This supports, Sperry's earlier findings that the 'left brain' and 'right brain' are distinct in terms of functions and abilities.

L- Therefore, this supports the scientific credibility of the biological approach, showing that brain lateralisation is a real and measurable phenomenon.

LIMITATION- OF SPERRY'S RESEARCH

P- One limitation is that causal relationships are hard to establish.

E- For example, in sperry's research the behaviour of the split-brain participants was compared to a neurotypical control group. However, non of the control group has epilepsy. Any differences between the grous may be due to epilepsy not the split-brain (cofounding variable).

E- This means that, some of the unique features of the split-brain participants cognitive abilities might have been due to their epilepsy.

L- Therefore, this lowers the internal validity of the research, as it’s unclear whether differences were caused by the split-brain procedure or by epilepsy.