Outline and evaluate research into lateralisation (16 marks)
Hemispheric lateralisation is defined as the idea that the brain is divided into two
hemispheres, and these two hemispheres have different functions. This is evident since
research demonstrates how the left hemisphere is the more logical side of the brain. This
side is therefore responsible for functions including language, maths, facts, sequencing and
linear thinking. Alternatively, the right hemisphere’s functions include visual motor tasks,
holistic thinking, rhythm, non-verbal cues and imagination. These two hemispheres are
connected by the corpus callosum and this facilitates interhemispheric communication.
Sperry and Gazzaniga conducted research into this concept using split brain patients, aiming
to examine the extent to which the two hemispheres are specialised for certain functions.
They conducted a range of tasks, including a tactile test where participants placed their hand
under a desk and held an object. In this task, they found that if the object was placed in the
left hand the participant was unable to describe what the object was but could make
guesses. However, if the object was placed into the right hand then the participants could
verbally describe what they felt. Another task that they conducted was a drawing task. The
participants would be presented with the word ‘face’ on a screen and would then draw the
word they saw. The findings of this task were that the left hand could draw clearer pictures
which demonstrates the superiority of the right hemisphere for visual motor tasks. This was
further supported by the finding that pictures drawn by the right hand were less clear, as in
this condition the participants used their left hemisphere, as the word was shown in their
right visual field, and the left hemisphere was not dominant in visual functions. The study
therefore concluded that the left hemisphere was responsible for speech and language while
the right hemisphere is responsible for visual-spatial processing and facial recognition but
they did recognise some connectivity across the hemispheres, supporting the function of the
corpus callosum.
A limitation of research into hemispheric lateralisation is that it fails to consider that some
functions may not be limited strictly to one hemisphere. For example, Turk et al conducted a
case study on a patient, JW, and found that he was able to develop the ability to speak using
the right hemisphere and this therefore reflects that language may not be restricted only to
the left hemisphere. This reflects that while one hemisphere is usually dominant, this does
not mean that the other hemisphere is completely incapable of its functions. This indicates
that hemispheric lateralisation may be less of a polarised process and there could be a
greater level of connectivity across the two hemispheres and therefore when necessary
some functions are able to be shared. However, the population validity of this research limits
its generalisability. The use of case studies focuses on one individual, and this is often
focused on an individual with an atypical brain structure and therefore this may not reflect
the functioning of the brain throughout the population. Additionally, this research focused on
language functioning and therefore the connectivity across the hemispheres may only be
applicable in this way for certain functions. However, while this research may lack validity to
some degree, this is important as it suggests that the brain is more adaptable than indicated
by early research, e.g. Gazzaniga who found the right couldn’t even learn basic language,
which can be important when treating patients who have experienced damage to either of
their hemispheres as we can recognise that they may not have completely lost certain
abilities.
,A strength of research into hemispheric lateralisation is that it can be used to identify
advantages of this, for example, that it can increase our neural processing ability, This was
studied by Rogers et al who found that in domestic chicken, brain lateralisation was
associated with and increased ability to multitask. This shows that this increases our brain
efficiency in certain cognitive tasks that require simultaneous use of our hemispheres but for
different functions. This finding is important as it supports the idea of hemispheric
lateralisation by demonstrating how the two hemispheres can complete separate tasks and
functions and therefore operate independently. This recognition that the two hemispheres
can be used simultaneously for two different functions is useful to identify ways that our brain
efficiency can be increased and this can be used to enhance productivity in humans.
Therefore, this is important when considering the wider implications of this research as this
could be a consideration in the workplace to enable workers to be able to focus on two tasks
if they require the use of both hemispheres, which consequently will have a positive impact
on the economy.
A limitation of research into lateralisation is that it changes with age and therefore is not
identical for all people since it varies across individuals. This is evident since Szaflarski et al
found that language was more lateralized to the left hemisphere with increasing age in
children but after they reached 25, this lateralisation decreased. They found that lateralized
function in younger people would switch to bilateral patterns in healthy older adults. While
there is no confirmed reason for this late decline, a likely possibility is that extra processing
resources in the other hemisphere compensate for the decline in function as our age
increases. This indicates that individual differences may exist within lateralisation and
therefore these processes are less fixed and can adapt and change throughout an
individual’s lifetime. This is important as when conducting research, the researcher should
consider this when choosing a sample as a predominantly younger sample could produce
different findings and conclusions than what may be concluded from an older sample. This
would affect the generalisability of this research and a more idiographic approach may be
needed in future research to ensure these variations across individuals are taken into
account.
A further limitation of research into lateralisation as a whole is that findings are often difficult
to generalise. Andrewes contends that many studies use a small sample, often just 3
participants, and sometimes even less. This means that conclusions are drawn despite the
confounding variable of a physical disorder which creates variation in comparison to the
typical brain structure. Split brain patients have often suffered from a disorder which is often
the reason that they have even had this procedure and these patients also sometimes do not
have a complete sectioning of hemispheres in the same way most people do. Therefore, a
lot of research into this area has limited generalisability as they are based on the anatomical
structure of people who have atypical brain structures. Additionally, the people used in this
research may be on medications and this creates even further variation to the functioning of
their brain as they may have varying levels of neurotransmitters to regulate certain functions.
This is important as conclusions from this research therefore may not be completely
applicable to many people and while the key findings of this research are likely to be true,
certain aspects of the findings may be exaggerated due to potentially reduced lateralisation
in split brain patients.
, ESSAY PLAN: Fight or flight
AO1: Short term response
- A person enters a stressful or dangerous situation
- The amygdala, which is part of the limbic system, then is activated which sends a
distress signal to the hypothalamus
- The hypothalamus then activates the sympathomedullary pathway (SAM system),
which is the pathway that runs to the adrenal medulla and the sympathetic nervous
system
- The sympathetic nervous system then stimulates the adrenal medulla which is part of
the adrenal gland
- The adrenal medulla secretes adrenaline and noradrenaline into the bloodstream
- Adrenaline causes a range of physiological changes to prepare the body for fight or
flight
AO1: Long term response (as in to long term stressors)
- If the brain continues to perceive something as a threat a second system kicks in
- The hypothalamus activates the HPA axis in response to a continued stress
response
- This consists of the hypothalamus, pituitary gland and adrenal glands
- The axis relied on hormonal signals to keep it working so corticotrophin releasing
hormone (CRH) is released from the hypothalamus and this enters the bloodstream
in response to a stressor
- CRH causes the pituitary gland to produce and release adrenocorticotrophic
hormone (ACTH) and this is then transported in the bloodstream to the adrenal
glands
- ACTH then stimulates the adrenal cortex to release stress related hormones
including cortisol which is responsible for many effects in the body that are needed
for fight or flight which can be positive (quick energy burst) or negative (impaired
cognitive performance)
- This system is also effective at regulating itself as the hypothalamus and pituitary
gland have receptors that monitor circulating cortisol levels and if these rise above
normal they initiate a reduction in CRH and ACTH which normalises cortisol levels
AO3: Application into treatment
Evidence: Youl-Ri Kima et al studied anorexia sufferers in the UK and found that doses of
oxytocin could reduce their focus on food and body image
Explanation: This reflects that application of one hormone involved in this response can have
positive implications for society. The application of this research is therefore useful since it
can be used to improve the mental health of the public and biological treatments are often
favoured as they are cheap and lack effort
Link: This matters because applying the biology of this research into treatments to resolve
complex psychological disorders will have an overall positive impact on the country’s mental
health and also therefore positively impacts the economy by reducing the burden on the
NHS mental health services and creating a more productive workforce
AO3: Doesn’t tell the whole story (reductionist)
