hemispheric lateralisation

Question 1

what is hemispheric lateralisation?

Answer 1

the idea that the two halves of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other

Question 2

how is language lateralised?

Answer 2

• two main centres are only in LH for most people
• broca’s area is in left frontal lobe
• wernicke’s area is in left temporal lobe
• language is performed by one hemisphere rather than the other

Question 3

how does the RH contribute to language?

Answer 3

• produces rudimentary words and phrases
• contributes emotional context to what is being said

Question 4

what role do LH and RH play in language?

Answer 4

• LH is analyser
• RH is synthesiser

Question 5

which functions are not lateralised?

Answer 5

vision, motor, and somatosensory areas appear in both hemispheres

Question 6

how is the motor area wired?

Answer 6

• motor area is cross-wired (contralateral wiring)
• RH controls movement on left side of body
• LH controls movement on right side of body

Question 7

how does the visual cortex receive information?

Answer 7

• contralateral (opposite) and ipsilateral (same-sided) wiring
• each eye receives light from left visual field (LVF) and right visual field (RVF)
• LVF of both eyes is connected to RH
• RVF of both eyes is connected to LH

Question 8

what is the benefit of vision being wired in the way that it is?

Answer 8

• enables visual areas to compare the slightly different perspective from each eye
• aids depth perception

Question 9

how is auditory input received?

Answer 9

• similar arrangement for auditory input to auditory area as there is for vision
• disparity from the two inputs helps us locate the source of sounds

Question 10

evaluation: lateralisation in the connected brain

Answer 10

• research showing that even in connected brains the 2 hemispheres process information different
• fink et al. (1996) used PET scans to identify which brain areas were active during a visual processing task
• when pts with connected brains were asked to attent to global elements of an image (eg. looking at a picture of a whole forest) regions of the RH were much more active
• when required to focus in on finer detail (eg. individual trees), specific areas of LH tended to dominate
• this suggests that for visual processing at least, hemispheric lateralisation is a feature of the connected brain as well as the split-brain

Question 11

evaluation: one brain

Answer 11

• LH as analyser and RH as synthesiser may be wrong
• may be different functions in the RH and LH, but research suggests people do not have a dominant side of their brain which creates a different personality
• nielsen et al. (2013) analysed brain scans from over 1000 people aged 7-29 and found that people used certain hemispheres for certain tasks (evidence for lateralisation) but there was no evidence of a dominant side
• this suggests that the notion of right- or left-brained people is wrong

Question 12

evaluation: lateralisation vs. plasticity

Answer 12

• lateralisation is adaptive as it enables 2 tasks to be performed simultaneously with greater efficiency
• rogers et al. (2004) showed that lateralised chickens could find food while watching for predators but ‘normal’ chickens could not
• however, neural plasticity could also be seen as adaptive
• following damage through illness or trauma, some functions can be taken over by non-specialised areas in the opposite hemisphere
• eg. language function can switch side (holland et al. 1996)