Discuss hemispheric lateralisation

Question 1

Summary

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 production of spoken language

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

Wernicke’s area is localised in the left parietal lobe, posterior to the auditory area

Responsible for langue comprehension, it contains a store of the sounds of words required to understand speech

Visual and spatial tasks like drawing and facial recognition are lateralised to the left hemisphere

Evidence for the left lateralisation of language comes from language aphasias where lesions in the left hemisphere caused impaired language abilities. 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 hemispehre

Question 2

Strength

Answer 2

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 other 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

Concept of language being lateralised to the left hemisphere has been challenged by refuting 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 language centres recovered by developing the ability to speak from his right hemisphere

This suggests that after the injury, the brain is able to recognise 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

Additional refuting research form Beaumont (1988)

Who found that in their meta-analysis, 5% of right handed participants showed a right hemispheric lateralisation for language

75% of left handed participants showed a bilateral representation for langue

This suggests that language is not always lateralised to the left hemisphere, like lateralisation predicts