hemispheric laterlaistion and split-brain research Flashcards
hemispheric lateralisation
localisation and lateralisation
localisation - some functions such as vision and language are governed by very specific areas of the brain
lateralised - two sides of the brain (hemispheres)
For some functions the localised areas appear in both hemispheres
example - in the case of vision the visual area is in the left and right occipital lobe - located in the left hemisphere and right hemisphere
hemispheric lateralisation
left and right hemisphere - language
in the case of language the two main centres are only in the left hemisphere
Broca’s areas is in the left frontal lobe
Wernickes areas is in the left temporal lobe
lanaguge is lateralised - that is performed by one hemisphere rather than the other r
the right hemisphere can only produce rudimentary words anf phrases but contributes emotional context to what is being said
led to the suggestion that the left hemisphere is the analyser whilst the right hemisphere is the synthesiser
hemispheric lateralisation
left and right hemispheres - movement
in the case of the motor area the brain is cross-wired (contra lateral wiring)
the right hemisphere control movement on the left side of the body whilst the left hemisphere cottons movement on the right
hemispheric lateralisation
left and right hemispheres - vision
vision is both contra lateral and ipsilateral (opposite and same sided)
each eye receives light from the left visual fields and the right visual field
the left visual field of both eyes is connected to the right hemisphere
the right visual field of both eyes is connected tot he left hemisphere
this enables the visual areas to compare the slightly different persepcuve from each eye and aids depth perception
similar arrangement for audorty input to the auditory areas and the disparity from the two inputs helps us locate the source of sounds
strength
lateralisation in the connected brain
research showing that even in connected brains the two hemispheres process information differently
Gereon Fink et al used PET scans to identify which brain areas were active during the visual processing task
when participants with connected brains were asked to attend to global elements of an image (such as looking at a picture of a whole forest)
regions of the right hemisphere were much more active
when required to focus in on the finer detail such as individual trees the specific areas of the left hemisphere tended to dominate
suggests that at least for visual processing hemispheric lateralisation is a feature of the connected brain as well as the split-brain
limitation
one brain
left hemisphere as analyser and right hemisphere as synthesiser may be wrong
may be different functions of the right hemisphere and the left hemisphere
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 did fid that people used certain hemispheres for certain tasks (evidence for lateralisation)
there was not evidence og a dominant side
suggests that the notion of right to left brained people is wrong
split-brain research
split brain research studies show how the hemispheres function when they cannot communicate with each other
Split-brain research - Sperrys research procedure
study how two separated hemispheres deal with speech and vision
11 people who had a split brain operation were studied
using a set up in which an image could be projected to a participants right vision field which is processed by the left hemisphere
then the same or different image would be projected to the left vision filed which is processed by the right hemisphere
in the normal brian the corpus colloquial would immediately share the information between both hemispheres giving a complete picture of the visual world
presenting the image to one hemisphere of a split brain participant meant that the information cannot be conveyed from that hemisphere to another
split brain research sperrys research findings
when a picture of an object was shown to a participants right vision field which is linked to the left hemisphere the participant could describe what was seen
they could not do this is the object was shown to the left field of vision which is controlled but the right hemisphere - they stated that there was nothing there
this is because in the connected brain messaged from the right hemisphere are relayed to the language centres in the left hemisphere
this is not possible in the split brain
although participants could not give verbal labels to objects projected to the left vision field they could select a matching object out of sight using their left hand
the left hand was also able to select an object that was most closely associated with an object represented to the left vision field
if a pinup was shown to the left vision filed there was an emotional reaction but the participants susually reported seeing nothing to just a flash of light
split brain research sperrys research - conclusions
these observations show how certain functions are lateralised in the brain and support the view that the left hemisphere is verbal and the right hemisphere is silent but emotional
strength
research support
research support from more recent split brain research
Gazzaniga showed that split-brain participants actually perform better than connected controls on certain tasks
example - they were faster at identifying the pff one out in an array of similar objects than normal controls
in the normal brian the left hemispheres better cognitive strategies are watered down by the inferior right hemisohere
supports sperrys earlier findings that the left brian and right brian are distinct
limitation
generalisation issues
casualty relationships are hard to establish
behaviour of sperrys split-brain participants was compared to neurotypical control group
an issue is that none of the participants in the control group had epilepsy
this is a major confounding variable
any difference that were observes between the two groups may be the result of the epilepsy rather than the split brain
means that same of the unique features of the split-brian paritpcaonts cognitive abilities might have been due to their epilepsy
