biopsychology: hemispheric lateralisation and split-brain research Flashcards
(22 cards)
What is hemispheric lateralization?
The idea that the two halves (hemispheres) of the brain are functionally different and certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other.
What does split-brain research investigate?
The extent to which the two hemispheres of the brain govern different functions, involving patients who had experienced surgical separation of the two hemispheres.
Which hemisphere controls the ability to produce and understand language?
The left hemisphere.
What connects the two hemispheres of the brain?
The corpus callosum > a bundle of nerve fibres that connect the two halves
What is the purpose of the corpus callosum?
To allow information received from one hemisphere to be sent to the other hemisphere.
What is a ‘split-brain’ patient?
Patients who have had their corpus callosum surgically cut to prevent epileptic seizures from crossing between hemispheres.
What was the aim of cutting the corpus callosum in patients?
To prevent the violent electrical activity that accompanies epileptic seizures from crossing from one hemisphere to the other.
What did Sperry’s procedure involve?
Projecting an image or word to a patient’s right visual field (processed by the left hemisphere) and ask them to say the word then do the same to the left visual field (processed by the right hemisphere)
What happens in a normal brain when an image is presented to one hemisphere?
The corpus callosum shares the information between both hemispheres, giving a complete picture of the visual field.
What was the result when a picture was shown to a patient’s right visual field?
The patient could easily describe what was seen.
What was the result when a picture was presented to the left visual field?
The patient could not describe it and often reported that there was nothing there.
Why could split-brain patients not describe objects in the left visual field?
Due to the lack of language centres in the right hemisphere > messages cannot be relayed between the left and right hemisphere
explain the procedure for the touch recognition
The objects were hidden behind a screen so that they could not see them. The left hand was also able to select an object most closely associated with the object presented (e.g. select an ashtray when shown a cigarette) to the left visual field.
* Although again they could not verbalise what they were selecting.
What could patients do with their left hand when objects were presented to the left visual field?
They could select a matching object from a grab-bag of different objects.
What conclusion can be drawn about the right hemisphere based on the ability to select objects?
The right hemisphere cannot verbalize but can still understand what is seen by the left eye.
What can we conclude about brain lateralization?
Certain functions are lateralized in the brain; the left hemisphere is verbal, and the right hemisphere is silent.
explain participants of the split-brain research
Sperry used 11 split brain patients who had their corpus callosum removed as a result of suffering from Epilepsy
He then compared the data to a control group whereby the participants had no history of Epilepsy
explain weaknesses of the sample
comparison groups were not valid
- The disconnection between the hemispheres was greater in some patients than others
- Some patients had experienced drug therapy for much longer than others
- Small sample sizes (11 ppts), cannot generalise the findings.
- comparison groups were not valid as any differences may have been the result of the Epilepsy rather than the split brain
AO3: differences may be overstated > functional recovery
One weakness of split-brain research is that the differences in function may be overstated.
Sperry suggests that the left and right hemisphere are responsible for different functions. The left hemisphere is responsible for speech production, while the right hemisphere is dominant in terms of facial recognition and its drawing abilities. However, it has been suggested the distinction is less clear cut. Instead the two hemispheres are in constant communication. This is supported by functional recovery, which suggests the functions of the damaged areas may be taken over by non-specialised areas in the opposite hemisphere (recuitment of homologous areas). for example, language areas may become controlled by the right hemisphere.
WEAKNESS as functions may not be lateralised to just the left or right hemisphere. Since, the functions may be redistributed if necessary
AO3: research to support lateralisation
One strength is research showing that even in connected brains the two hemisphere process information differently
Fink et al used PET scans to identify which brain areas were active during a 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 details (such as individual trees) the specific areas of the left hemisphere dominated.
STRENGTH as this suggests that, as at least as far as visual processing is concerned, hemispheric lateralisation is a feature of the connected brain as well as split-brain
AO3: split-brain research to support
One strength is support from more recent split-brain research
Gazzangia showed that split-brain participants actually perform better than connected controls on certain tasks. For example, they were faster at identifying the odd one out in an array of similar objects than normal controls. In the normal brain, the left hemisphere’s better cognitive strategies was weakened by the inferior right hemisphere.
STRENGTH as this supports Sperry’s idea that the left hemisphere and right hemisphere are distinct.
AO3: poor generalisation
One limitation of Sperry’s research is that causal relationships are hard to establish
Sperry compared the behaviour of his 11 split-brain patients with epilepsy to a neurotypical control group who had no history of epilepsy.
WEAKNESS as the patients having epilepsy acted as a confounding variable. Any differences observed between the two groups may be the result of the epilepsy rather than the split brain. This means that some of the unique features of the split-brain participants’ cognitive abilities might have been due to their epilepsy
