outline and evaluate research into lateralisation

Question 1

outline

Answer 1

Language is lateralised in the left hemisphere: Broca’s area is localised in the left frontal lobe, anterior to the motor area, and is responsible for the production of spoken language.

It contains the plans for motor movement required to speak each word, which it sends to the motor area to carry out the necessary movements of the mouth and larynx during speech.

Similarly, Wernicke’s area is localised in the left parietal lobe, posterior to the auditory area. Responsible for language comprehension, it contains a store of the sounds of words required to understand speech.

Conversely, visual and spatial tasks like drawing and facial recognition are lateralised to the right hemisphere.
- Evidence for the left lateralisation of language comes from language aphasias, where lesions in the left hemisphere caused impaired language abilities.

The findings from historic case studies (such as Broca’s Aphasia patient ‘Tan’) have been confirmed by modern PET scans.

Evidence for right hemisphere dominance for visual and spatial tasks also come from Sperry’s divided field experiments where split brain participants could easily identify faces and were able to accurately draw symbols presented in their left visual field, suggesting many complex visual and spatial tasks must be lateralised to the right hemisphere.

Question 2

strength

Answer 2

A strength of lateralisation is that it is related to increased neural processing.

This is because it allows for multi-tasking, as only using one hemisphere to engage in a task leaves the other hemisphere free to engage in another functions.

Rogers et al (2004), found that hemispheric lateralisation allowed chickens to perform 2 tasks simultaneously (finding food and being vigilant for predators).

This suggests that brain lateralisation enhances brain efficiency in cognitive tasks that demand the simultaneous but different use of both hemispheres.

Question 3

limit 1

Answer 3

However, the concept of language being lateralised to the left hemisphere has been challenged by refusing research evidence.

This is when research is criticised by strong or convincing evidence.

For example, Turk et al (2002) identified patient J.W who even after brain damage to his left hemisphere, his langue centres recovered by developing the ability to speak from his right hemisphere.

This suggests that after the injury, the brain can reorganise itself and recruit similar areas in the opposite hemisphere to take over the function that has been lost (functional recovery), ultimately challenging the concept of lateralisation.

Question 4

limit 2

Answer 4

Another limitation is that there is additional refuting research from Beaumont (1988) who found that in their meta-analysis, 5% of right-handed participants showed a right hemispheric lateralisation for language and 75% of left-handed participants showed a bilateral representation for language.

This suggests that language is not always lateralised to the left hemisphere, like lateralisation would predict.

Question 5

limit 3

Answer 5

Finally, research has demonstrated individual differences in lateralisation, which is when there is variability between different groups of participants, which the concept of lateralisation does not account for.

For example, Szaflarski et al., (2006) found that language is lateralised in the left hemisphere in children and adolescents, but after the age of 25, lateralisation decreased with each decade of life.

This suggests that as we get older, we recruit the other hemisphere to compensate for age related decline in function, challenging the concept that language is lateralised to the left hemisphere only in all age groups.