Biopsychology
Wednesday, 4 February 2026 7:54 am
16 marker: Discuss what research has shown about localisation of function in the brain.
PEELD: Strength
One strength is evidence from brain scans that support the idea that many everyday brain functions are localised. For
example, Petersen et al. (1988) used brain scans to demonstrate how Wernicke's area was active during a listening task and
Broca's area was active during a reading task. Furthermore, a review of long-term memory studies by Buckner and Petersen
(1996) revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. This shows that there
are distinct localised areas for everyday behaviours because each task consistently activates a specific, specialised region
rather than a broad or overlapping network. Therefore, objective methods for measuring brain activity have provided sound
scientific evidence that many brain functions are localised to specific regions of the brain, increasing the validity of
localisation of function. However, this idea is challenged by the work of Lashley (1950). Lashley removed areas of the
cortex ,between 10% and 50%, in rats that were learning the route through a maze. No area was proven to be more
important than any other area in affecting the rats' ability to learn the route. The process of learning seemed to require
every part of the cortex rather than being confined to a particular area. This suggests that higher cognitive processes, such as
learning are not as localised as Broca and Wernicke predict.
PEELD: Strength
Another strength of the localisation of function theory is that there is case study research to support the localisation of
language areas. As a result of epileptic seizures which caused damage to his Broca's area, Patient Tan lost the ability to
produce fluent speech and was only able to produce the word "Tan". This shows that his cognitive ability to produce speech
was dependent on a specific, localised region in the left frontal lobe as when it was damaged, his ability to produce speech
was severely stifled. Therefore, these findings provide strong evidence that language production is localised to a specific
brain area, increasing the validity of this central concept as it has been demonstrated that the loss of a particular cognitive
ability closely correlates to damage in a specific brain area. However, Dronkers et al. (2007) conducted an MRI scan on Tan's
brain. Although there was a lesion found in the Broca's area, they also found evidence to suggest other areas may have also
contributed to the failure in speech production. These results suggest that Broca's area may not be the only region
responsible for speech production and the deficits found in patients with Broca's aphasia could be the result of damage to
other neighboring regions, defusing the idea of specific localisation of speech production.
PEELD: Weakness
One weakness of the localisation of function theory is that some psychologists suggest it is more important to investigate
how the brain areas communicate with each other, rather than focusing on specific brain regions. Wernicke claimed that
although the different areas of the brain are independent, they must interact with each other in order to function. Dejerine
reported a man who lost his ability to read, following damage to the connection between the visual cortex and the
Wernicke's area. This shows that interactions between different areas produce complex behaviours such as language, rather
than it being produced by one isolated, localised region. Therefore, damage to the connection between any two points can
result in impairments that resemble damage to the localised brain region associated with that specific function, reducing the
credibility of the theory. Furthermore, critics also argue that theories of localisation are biologically reductionist in nature
and try to reduce very complex human behaviours and cognitive processes to one specific brain region. Such critics suggest
that a more thorough understanding of the brain is required to truly understand complex cognitive processes like language.
16 marker: Discuss research on hemispheric lateralisation.
PEELD: Strength
One strength is research showing that even in connected brains the two hemispheres process information differently. For
example, 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 detail, such as individual trees,
the specific areas of the left hemisphere tended to dominate. This shows that hemispheric lateralisation is a feature of the
connected brain as well as the split brain, particularly where visual processing is concerned. Therefore, this increases
construct/internal validity by providing strong biological evidence that lateralisation is a genuine feature of the normal brain.
However, whilst some lateralisation exists, it may not be as rigid for other functions such as language. Research has suggested
that lateralisation changes with age. For example, Szaflarki et al. found that language became more lateralised to the left
hemisphere with increasing age in children and adolescents, but after the age of 25, lateralisation decreased with each decade of
life. This raises questions regarding the extent of dominance that one hemisphere has over the other with particular functions.
PEELD: Strength
Another strength of lateralisation is that it increases neural processing capacity. Rogers et al. found that in a domestic chicken
brain, lateralisation is associated with an enhanced ability to perform two tasks simultaneously such as finding food and being
vigilant for predators. This means that using only one hemisphere to engage in a task allows the other hemisphere to freely
engage in other functions. Therefore, this suggests this increases the credibility of the explanation as it suggests that having two
separately functioning hemispheres would increase the chances of survival. However, it could also be argued that the brain’s
ability to reorganise itself challenges the idea that strict hemispheric lateralisation is always advantageous. Holland et al. found
that following trauma, functions can shift to the opposite hemisphere, with language even ‘switching sides’ in some cases. This
suggests that flexibility, rather than fixed lateralisation, may be the true evolutionary advantage, as the ability to reassign
functions increases survival after injury.
PEEL: Weakness
One limitation is the idea that the left hemisphere as analyser and right hemisphere as synthesiser may be wrong. There may be
different functions in the right hemisphere and left hemisphere, but research suggests people do not have a dominant side of
their brain which creates a different personality. Nielsen et al. analysed brain scans from over 1000 people aged 7 to 29 years
and did find that people used certain hemispheres for certain tasks, but there was no evidence of a dominant side such as
'artist's brain' or 'mathematician's brain'. This suggests that the notion of right or left brained people is inaccurate because
hemispheric lateralisation does not correlate with personality types. Therefore, this challenges the validity of assumptions about
fixed hemispheric dominance, suggesting it may be more task lateralised than person-lateralised.
16 marker: Discuss split-brain research.
PEELD: Weakness
One weakness of Sperry's research is the small and unique sample they used. In their research, only 11 epileptic patients were
studied. Small samples are susceptible to the effects of anomalies, and patients also experienced seizures which may have damaged
the brain through starvation of oxygen in certain areas. This means that other areas of the brain could have potentially started to
compensate for the damage, leading to changes in hemispheric lateralisation, and therefore changing the findings in relation to the
right and left hemisphere. Therefore, we cannot confidently generalise the results to non-epileptic patients as all of the research was
concluded on patients with atypical neurological profiles and so does not tell us much about how the two hemispheres operate in
healthy brains. Furthermore, there was no testing of patients prior to the surgery. This means that we do not know about their
functioning abilities prior to the severing of the corpus callosum. As a result, we cannot draw accurate conclusions about the effects
of the surgery as the differences observed in Sperry's tasks could simply reflect pre-existing abnormalities such as years of severe
epilepsy rather than the consequences of the split-brain procedure itself. This weakens the internal validity of the study as we
cannot establish a true cause-and effect relationship.
PEELD: Strength
One strength of Sperry's research is that there is support from more recent split-brain research. Luck et al. 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. Kingstone et al. argued that in the normal brain, the left hemisphere's
better cognitive strategies are 'watered down' by the inferior right hemisphere. This shows that the hemispheres are distinct, and
can apply their own specialised processing style more efficiently when working independently. Therefore, this increases the
credibility of Sperry's conclusions as his claims still remain valid and influential in modern cognitive neuroscience. However, some
researchers argue that even in split-brain patients, the brain can only produce one consciousness. Whilst visual perceptions remains
separate after surgery, consciousness can be shared across the brain. This suggests that the hemispheres may not operate as fully
separate cognitive units and that Sperry may have overstated the distinctiveness. As a result, more research should be conducted
with split-brain patients to determine what is and is not separate.
PEEL: Weakness
Another weakness of Sperry's research is that it raised ethical issues regarding the treatment of split-brain patients. Whilst the
participants did not undergo the operation for the purpose of the research and their full informed consent was obtained, they were
repeatedly exposed to confusing and disorientating tasks to investigate their cognitive abilities. This could have caused discomfort
and stress to the patients and they may have felt pressured to continue participating due to their gratitude and reliance on medical
professionals. Therefore, ethical issues surrounding consent and potential distress needs to be carefully outweighed with the
beneficial outcomes of the study.
Wednesday, 4 February 2026 7:54 am
16 marker: Discuss what research has shown about localisation of function in the brain.
PEELD: Strength
One strength is evidence from brain scans that support the idea that many everyday brain functions are localised. For
example, Petersen et al. (1988) used brain scans to demonstrate how Wernicke's area was active during a listening task and
Broca's area was active during a reading task. Furthermore, a review of long-term memory studies by Buckner and Petersen
(1996) revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. This shows that there
are distinct localised areas for everyday behaviours because each task consistently activates a specific, specialised region
rather than a broad or overlapping network. Therefore, objective methods for measuring brain activity have provided sound
scientific evidence that many brain functions are localised to specific regions of the brain, increasing the validity of
localisation of function. However, this idea is challenged by the work of Lashley (1950). Lashley removed areas of the
cortex ,between 10% and 50%, in rats that were learning the route through a maze. No area was proven to be more
important than any other area in affecting the rats' ability to learn the route. The process of learning seemed to require
every part of the cortex rather than being confined to a particular area. This suggests that higher cognitive processes, such as
learning are not as localised as Broca and Wernicke predict.
PEELD: Strength
Another strength of the localisation of function theory is that there is case study research to support the localisation of
language areas. As a result of epileptic seizures which caused damage to his Broca's area, Patient Tan lost the ability to
produce fluent speech and was only able to produce the word "Tan". This shows that his cognitive ability to produce speech
was dependent on a specific, localised region in the left frontal lobe as when it was damaged, his ability to produce speech
was severely stifled. Therefore, these findings provide strong evidence that language production is localised to a specific
brain area, increasing the validity of this central concept as it has been demonstrated that the loss of a particular cognitive
ability closely correlates to damage in a specific brain area. However, Dronkers et al. (2007) conducted an MRI scan on Tan's
brain. Although there was a lesion found in the Broca's area, they also found evidence to suggest other areas may have also
contributed to the failure in speech production. These results suggest that Broca's area may not be the only region
responsible for speech production and the deficits found in patients with Broca's aphasia could be the result of damage to
other neighboring regions, defusing the idea of specific localisation of speech production.
PEELD: Weakness
One weakness of the localisation of function theory is that some psychologists suggest it is more important to investigate
how the brain areas communicate with each other, rather than focusing on specific brain regions. Wernicke claimed that
although the different areas of the brain are independent, they must interact with each other in order to function. Dejerine
reported a man who lost his ability to read, following damage to the connection between the visual cortex and the
Wernicke's area. This shows that interactions between different areas produce complex behaviours such as language, rather
than it being produced by one isolated, localised region. Therefore, damage to the connection between any two points can
result in impairments that resemble damage to the localised brain region associated with that specific function, reducing the
credibility of the theory. Furthermore, critics also argue that theories of localisation are biologically reductionist in nature
and try to reduce very complex human behaviours and cognitive processes to one specific brain region. Such critics suggest
that a more thorough understanding of the brain is required to truly understand complex cognitive processes like language.
16 marker: Discuss research on hemispheric lateralisation.
PEELD: Strength
One strength is research showing that even in connected brains the two hemispheres process information differently. For
example, 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 detail, such as individual trees,
the specific areas of the left hemisphere tended to dominate. This shows that hemispheric lateralisation is a feature of the
connected brain as well as the split brain, particularly where visual processing is concerned. Therefore, this increases
construct/internal validity by providing strong biological evidence that lateralisation is a genuine feature of the normal brain.
However, whilst some lateralisation exists, it may not be as rigid for other functions such as language. Research has suggested
that lateralisation changes with age. For example, Szaflarki et al. found that language became more lateralised to the left
hemisphere with increasing age in children and adolescents, but after the age of 25, lateralisation decreased with each decade of
life. This raises questions regarding the extent of dominance that one hemisphere has over the other with particular functions.
PEELD: Strength
Another strength of lateralisation is that it increases neural processing capacity. Rogers et al. found that in a domestic chicken
brain, lateralisation is associated with an enhanced ability to perform two tasks simultaneously such as finding food and being
vigilant for predators. This means that using only one hemisphere to engage in a task allows the other hemisphere to freely
engage in other functions. Therefore, this suggests this increases the credibility of the explanation as it suggests that having two
separately functioning hemispheres would increase the chances of survival. However, it could also be argued that the brain’s
ability to reorganise itself challenges the idea that strict hemispheric lateralisation is always advantageous. Holland et al. found
that following trauma, functions can shift to the opposite hemisphere, with language even ‘switching sides’ in some cases. This
suggests that flexibility, rather than fixed lateralisation, may be the true evolutionary advantage, as the ability to reassign
functions increases survival after injury.
PEEL: Weakness
One limitation is the idea that the left hemisphere as analyser and right hemisphere as synthesiser may be wrong. There may be
different functions in the right hemisphere and left hemisphere, but research suggests people do not have a dominant side of
their brain which creates a different personality. Nielsen et al. analysed brain scans from over 1000 people aged 7 to 29 years
and did find that people used certain hemispheres for certain tasks, but there was no evidence of a dominant side such as
'artist's brain' or 'mathematician's brain'. This suggests that the notion of right or left brained people is inaccurate because
hemispheric lateralisation does not correlate with personality types. Therefore, this challenges the validity of assumptions about
fixed hemispheric dominance, suggesting it may be more task lateralised than person-lateralised.
16 marker: Discuss split-brain research.
PEELD: Weakness
One weakness of Sperry's research is the small and unique sample they used. In their research, only 11 epileptic patients were
studied. Small samples are susceptible to the effects of anomalies, and patients also experienced seizures which may have damaged
the brain through starvation of oxygen in certain areas. This means that other areas of the brain could have potentially started to
compensate for the damage, leading to changes in hemispheric lateralisation, and therefore changing the findings in relation to the
right and left hemisphere. Therefore, we cannot confidently generalise the results to non-epileptic patients as all of the research was
concluded on patients with atypical neurological profiles and so does not tell us much about how the two hemispheres operate in
healthy brains. Furthermore, there was no testing of patients prior to the surgery. This means that we do not know about their
functioning abilities prior to the severing of the corpus callosum. As a result, we cannot draw accurate conclusions about the effects
of the surgery as the differences observed in Sperry's tasks could simply reflect pre-existing abnormalities such as years of severe
epilepsy rather than the consequences of the split-brain procedure itself. This weakens the internal validity of the study as we
cannot establish a true cause-and effect relationship.
PEELD: Strength
One strength of Sperry's research is that there is support from more recent split-brain research. Luck et al. 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. Kingstone et al. argued that in the normal brain, the left hemisphere's
better cognitive strategies are 'watered down' by the inferior right hemisphere. This shows that the hemispheres are distinct, and
can apply their own specialised processing style more efficiently when working independently. Therefore, this increases the
credibility of Sperry's conclusions as his claims still remain valid and influential in modern cognitive neuroscience. However, some
researchers argue that even in split-brain patients, the brain can only produce one consciousness. Whilst visual perceptions remains
separate after surgery, consciousness can be shared across the brain. This suggests that the hemispheres may not operate as fully
separate cognitive units and that Sperry may have overstated the distinctiveness. As a result, more research should be conducted
with split-brain patients to determine what is and is not separate.
PEEL: Weakness
Another weakness of Sperry's research is that it raised ethical issues regarding the treatment of split-brain patients. Whilst the
participants did not undergo the operation for the purpose of the research and their full informed consent was obtained, they were
repeatedly exposed to confusing and disorientating tasks to investigate their cognitive abilities. This could have caused discomfort
and stress to the patients and they may have felt pressured to continue participating due to their gratitude and reliance on medical
professionals. Therefore, ethical issues surrounding consent and potential distress needs to be carefully outweighed with the
beneficial outcomes of the study.
