Hemispheric Lateralisation Flashcards
What is hemispheric lateralisation?
The idea the 2 halves of the brain function differently
=> certain processes / behaviour are dominated by 1 hemisphere rather than the other
How is movement lateralised?
Contralateral (crosswired)
- e.g. the left hemisphere controls the right side
How is vision lateralised?
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
How do the 2 hemispheres communicate?
Through the corpus callosum
=> a bundle of millions of nerve fibres (myelinated axons) that connect the 2 hemispheres
Split Brain Research - Sperry (1968)
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
Determining lateralisation of language
- 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
Determining lateralisation of visual/motor tasks
- 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
Determining lateralisation of emotions
- 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
Examples of other functions lateralised to the Left
- Language
- Music
- Analytical tasks
Examples of other functions lateralised to the Right
- Emotional content of language
- Drawing
- Facial recognition
- Spatial tasks
- Synthesier
(S) Support from more recent split-brain studies - Luck et al (1989)
- 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
(L) Issues with generalisation in Sperry’s Research
- 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
(S) Supporting evidence from Neurotypical brains - Fink et al
- 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
(L) The idea of analyser vs. synthesiser may be wrong - Nielsen et al (2013)
- 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
(L) Neural Plasticity - Tusk et al (2002)
- 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
