brain: hemispheric lateralisation Flashcards
what is hemispheric lateralisation?
Certain behaviours and mental processes are controlled or dominated by one hemisphere rather than the other.
which hemisphere is language controlled by?
left hemisphere, suggesting it has been subjected to hemispheric lateralisation
what does hemispheric lateralisation suggest about the left and right hemisphere?
they are fundimentally different
what is the bart of the brain that connects the two hemispheres?
the corpus callosum
how does the corpus callous allow the brain to work?
it allows the brain to work holistically
what is Rodger Sperry’s research into split brain patients?
A famous piece of research by Roger Sperry (1968) involved a unique group of individuals who had a surgical procedure known as a commissurotomy in which the corpus callosum which connects the two hemispheres is severed to prevent the spread of epileptic seizures across the brain.
what was the procedure for Sperry’s research?
An image/word was projected to a participants right visual field (processed by the left hemisphere).
And a different image could be projected to the left visual field (processed by the right hemisphere).
In the normal brain the corpus callosum would share the info between both hemispheres giving a complete picture of the visual world.
what were the key findings for the study when participants had to describe what they could see?
When a picture of an object was shown to a participants right visual field, the participant could describe what was seen.
BUT if the same object was shown to the left visual field, the participant couldn’t describe what was seen and usually said there was nothing there.
WHY?
For most people language is processed in the left Hemisphere.
So the participants inability to describe objects in the left visual field was because of the lack of language centres in the right Hemisphere.
what were the key findings of the study when the participants were asked to recognise what they were touching?
In each case the patient wasn’t able to verbally identify what they had seen but could still ‘understand’ what the object was, using the right hemisphere and therefore could select the corresponding object OR draw the object WITH THEIR LEFT HAND
AO3: how is ‘scientific status’ a strength to hemispheric lateralisation of the brain?
One strength to hemispheric lateralisation of the brain is that it has scientific status. For example, Sperry carried out his experiment in a lab where other variables were controlled meaning the research was highly standardised. His high levels of control meant that the individuals were unable to spread information across both hemispheres increasing the validity of his findings. His research was also more ethical as he chose participants who had already undergone the split brain surgery, not picked participants and then carried out the surgery on them. Therefore, Sperry’s research can claim scientific status as a cause and effect relationship can be established due to the high levels of control over extraneous variables. However, this research may lack mundane realism as its done in a lab setting we are unable to understand how the brain may work in more realistic situations.
AO3: how is ‘inappropriate control group’ a limitation to hemispheric lateralisation of the brain?
One limitation to Sperrys research into hemispheric lateralisation of the brain is the type of control group he used. For example, he used a control group of normal people and compared them to the participants with epilepsy and split brain surgery. This means that he should’ve used a control group of epileptic patients to avoid confounding variables in the research. Therefore, the research lacks validity as we cant generalise the findings due to the inappropriate control group.
AO3: how is ‘supporting evidence’ a strength to hemispheric lateralisation of the brain?
One strength to hemispheric lateralisation of the brain is that it has supporting evidence. For example, Fink et al (1996) used PET scans to identify areas of the brain active when doing a visual processing task. They found that when looking at an image, a picture of a whole forest, regions of the right hemisphere were much more active. Whereas, when looking at more specific details, such as looking at individual trees, specific areas of the left hemisphere were more active. Therefore, this suggests that each hemisphere performs different functions when performing visual tasks.
AO3: how is ‘neural plasticity’ a limitation to hemispheric lateralisation of the brain?
One limitation to hemispheric lateralisation of the brain is brain plasticity and functional recovery. This suggests that the brain is not too fixed in structure in case of an injury as following damage through illness or trauma, some functions can be taken over by non-specialised areas in the opposite hemisphere. For example, Turk et al (2002) discovered a patient who suffered damage to the left hemisphere but developed the capacity to speak in the right hemisphere, leading to the ability to speak about the information presented to either side of the brain. Therefore, this suggests that lateralised functions are flexible rather than fixed and this would be an adaptive characteristic of the nervous system.
A03: how is ‘challenging evidence’ a limitation to hemispheric lateralisation?
One limitation to hemispheric lateralisation of the brain is that it has challenging evidence. For example, Nielsen et al (2013) analysed brain scans from 1000 people aged 7-29 years and found that certain hemispheres were used for specific tasks. However, there was no such evidence of a dominant hemisphere, therefore suggesting that the idea of a left or right brained person is false.
