Hemispheric Lateralisation

Question 1

What is hemispheric lateralisation?

Answer 1

The idea the 2 halves of the brain function differently
=> certain processes / behaviour are dominated by 1 hemisphere rather than the other

Question 2

How is movement lateralised?

Answer 2

Contralateral (crosswired)
- e.g. the left hemisphere controls the right side

Question 3

How is vision lateralised?

Answer 3

Contralateral +Ipsilateral (crosswired + on the same side)
- e.g. info from R visual field of each eye is processed by L side and vice versa

Question 4

How do the 2 hemispheres communicate?

Answer 4

Through the corpus callosum
=> a bundle of millions of nerve fibres (myelinated axons) that connect the 2 hemispheres

Question 5

Split Brain Research - Sperry (1968)

Answer 5

Investigated lateralisation in epilepsy patients after they had their corpus callosum + other tisuses connecting hemispheres

=> the 2 hemispheres could not communicate
=> can see what functions occur in each

Question 6

Determining lateralisation of language

Answer 6

• Procedure: Image/word shown to L visual field (processed by R hemisphere) or R visual field (processed by left)
• Findings: Image/word presented to RVF could be verbally described but not those on the left (would say nothing’s there)
• Conclusions: Language is lateralised to left hemisphere as Broca’s area + Wernicke’s area located there

Question 7

Determining lateralisation of visual/motor tasks

Answer 7

• Images presented in LVF could still trigger movement in the left hand
• With an object placed in left hand, could select a similar object by touch (but can’t verbally describe)

Therefore => visual motor tasks are lateralised to the right hemisphere

Question 8

Determining lateralisation of emotions

Answer 8

• Images/words presented to LVF could trigger emotional reaction like laughing
• However, pps could still not verbally describe the image

Therefore => emotions are lateralised to the right hemisphere

Question 9

Examples of other functions lateralised to the Left

Answer 9

• Language
• Music
• Analytical tasks

Question 10

Examples of other functions lateralised to the Right

Answer 10

• Emotional content of language
• Drawing
• Facial recognition
• Spatial tasks
• Synthesier

Question 11

(S) Support from more recent split-brain studies - Luck et al (1989)

Answer 11

• Showed split-brain pps are better than normal controls (e.g. 2x as fast at identifying odd ones out in similar objects)
• In normal brains, LH’s processing abilities are dampened by inferior RH (Kingstone et al, 2015)

Supports => Sperry’s earlier findings that left + right brain are distinct

Question 12

(L) Issues with generalisation in Sperry’s Research

Answer 12

• Control group did not have epilepsy (were neurotypical - confounding variable ) as well as having a corpus callosum
• Very small sample size of 11

Suggests => Sperry’s research lacks external validity as unique features of split brain pps may be due to epilepsy

Question 13

(S) Supporting evidence from Neurotypical brains - Fink et al

Answer 13

• PET scans of people looking at an image
• Activity in R hemisphere for global parts of picture
• Activity in L hemisphere for finer details

Suggests => visual processing is lateralised between 2 hemispheres + that hemispheric lateralisation is normal

Question 14

(L) The idea of analyser vs. synthesiser may be wrong - Nielsen et al (2013)

Answer 14

• May be diff. functions in the RH and LH but research suggest ppl don’t have a dominant side
• Analysis of 1000 brain scans aged 7-22 yrs - certain Hs for certain tasks but no dominance

Suggests => the notiom of right- or left- brained ppl is wrong

Question 15

(L) Neural Plasticity - Tusk et al (2002)

Answer 15

• Following brain damage, some functions can be taken over by opposite hemisphere
• Case study of JW who developed capacity to speak in RH
• Could eventually speak about information in L or R VF

Suggests => ppl aren’t left or right brained despite some functions being lateralised