Lateralisation and Split Brain Research

Question 1

Hemispheric lateralisaiton

Answer 1

Certain mental processes and behaviours are controlled or dominated by one hemisphere rather than the other (as in the example of language)

Question 2

Split brain studies

Answer 2

Corpus callosum cut in patients with severe epilepsy, allowing researchers to investigate the extent to which brain function is lateralised.

Question 3

Procedures

Answer 3

Image/word is projected to right visual field or left visual field.

Question 4

Describing what you see

Answer 4

Pictures shown to RVF could be described but not those to LVF because no language centres in the right hemisphere (connected to LVF)

Question 5

Recognition by touch

Answer 5

Could not describe objects projected to LVF, but able to select a matching object from a selection of different objects using their left hand.

Question 6

Lateralisation

Answer 6

The brain is divided into two halves; right & left hemispheres.

This is known as lateralisation – there is a difference in some physical and psychological functions controlled by each hemisphere.

Generally the left side of the body is controlled by the right hemisphere; and the right side of the body by the left hemisphere.

Question 7

Left Hemisphere

Answer 7

Sensory stimulus from right side of the body
Motor control of right side of body
Speech, language and comprehension
Analysis and calculations
Time and sequencing
Recognition of words, letters and numbers

Question 8

Right Hemisphere

Answer 8

Sensory stimulus from left side of the body
Motor control of left side of the body
Creativity
Spatial ability
Context/perception
Recognition of faces, places and objects.

Question 9

Hemispheric Lateralisation

Answer 9

Hemispheric lateralisation is the theory that each
hemisphere of the brain has specific functions

This is a widely accepted viewpoint in psychology and
medicine

This is due to a large body of evidence supporting
these claims – eg. The ‘speech centres’, Broca’s area and Wernicke’s area appear only to exist in the left
hemisphere

Question 10

Hemispheric Lateralisation

Answer 10

Information from our right
visual field (RVF) is processed
in our left hemisphere

Information from our left
visual field is processed in the
right hemisphere

The two hemispheres
communicate via the Corpus
Callosum

Question 11

The Corpus Callosum

Answer 11

The Corpus Callosum connects the two hemispheres of the brain and allows us to use both sides together

Eg. Talking about things (speech = left) that are experienced in the right hemisphere

Question 12

Split-Brain Research

Answer 12

Unique research opportunities have arisen, where patients whose Corpus Callosum’s have been cut, can be participants

This allows psychologists to observe how the brain can work when information from hemisphere’s cannot be communicated in the usual way

Such research provides strong evidence for the case that our brains are lateralised (each hemisphere has specific functions) and we are able to function effectively (with a ‘whole’ brain) because of the Corpus Callosum

Question 13

Key Study: Sperry & Gazzaniga

Answer 13

If the Corpus Callosum was cut, this would mean that information from
each hemisphere couldn’t pass between the two

This would disable some functions that are only available in one hemisphere, such as speech

Question 14

Sperry – Procedure

Answer 14

Procedure:

-Quasi-experiments

-11 split-brain patients (due to severe epilepsy)

-Performance on tasks compared with people without
split-brain

• This involved blindfolding one of the participant’s eyes and then asking
  them to fixate with the seeing eye on a point in the middle of a screen.
  The researchers would then project a stimulus on either the left or right
  hand side of the fixation point for less than 1/10 of a second
• As language is processed in the left hemisphere, when a stimulus is
  presented to the left visual field of a split-brain patient they should not
  be able to name the stimulus.

Question 15

What happens in the split-brain?

Answer 15

Sperry’s research shows that if a split-brain patient is shown an image to their right visual
field, they can state what this is (as info from RVF passes directly to left hemisphere where
the brain’s speech centres are).

However, the left visual field would connect directly to the right hemisphere, where there is
no speech centre. In a ‘normal’ brain, this info would pass across the corpus callosum to
the left hemisphere speech centre so the information can be verbalised.

In a split-brain patient, there is no connection to cross, so the information goes nowhere
and the person cannot verbalise the image. They could however, draw it, as their motor
control is unaffected

Question 16

Split brain research: Sperry & Gazzaniga - 3 key findings:

Answer 16

Patients can verbalise an image shown to their right visual field (because the left hemisphere
contains the speech centres)

Patients cannot verbalise an image shown to their left visual field (because the right hemisphere
processes this but contains no speech centre) BUT they can draw it with their left hand (the right
hemisphere has dominant motor function)

If a patient is shown an image in both visual fields, they will say they’ve seen the one in the Right
visual field (processed by left hemisphere), but draw the image they’ve seen in the LVF, with their
left hand.

Question 17

Evaluating Split-brain research

Answer 17

You are evaluating how split brain research can help inform our understanding of how the brain is lateralised

Example evaluation point (limitations of split brain research)

“A limitation of split-brain research is that sample sizes are limited and could be misinforming
our understanding of lateralisation in the brain.

As the split-brain procedure is a last resort for severe epilepsy and not many other conditions, psychologists only have access to small numbers of research participants. Research suggests this can even be one single participant, or groups as small as three.

Therefore, split-brain research has been criticised for drawing wide-scale conclusions about
hemispheric lateralisation that may have been specific to certain participants. Such cases may not even be applicable to the wider population and should not be used to inform general
understanding of lateralisation in the brain”.

Question 18

Methodological Evaluation 1

Answer 18

+ Sperry’s research was very well designed with standardised procedures.

+ As he made use of presenting information to one eye whilst the other was blindfolded and he flashed the image up extremely quickly he had properly controlled which hemisphere was being exposed.

+ His procedure could be replicated so his findings could be validated.

• But he used small samples so we can’t generalise
• And they had a disorder that could act as a confounding variable
• The split-brain procedure is rarely carried out these days.
• Therefore patients who have had this procedure are rarely encountered in sufficient numbers to be useful for research.

Question 19

Methodological Evaluation 2

Answer 19

A limitation of split-brain research is that sample sizes are limited and could be
misinforming our understanding of lateralisation in the brain.

As the split-brain procedure is a last resort for severe epilepsy and not many other
conditions, psychologists only have access to small numbers of research
participants. Research suggests this can even be one single participant, or groups as
small as three.

Therefore, split-brain research has been criticised for drawing wide-scale
conclusions about hemispheric lateralisation that may have been specific to certain
participants. Such cases may not even be applicable to the wider population and
should not be used to inform general understanding of lateralisation in the brain.

Question 20

Methodological Evaluation 3

Answer 20

+ Sperry’s research was very well designed with standardised procedures.

+ As he made use of presenting information to one eye whilst the other was blindfolded and he flashed the image up extremely quickly he had properly controlled which
hemisphere was being exposed.

+ His procedure could be replicated so his findings could be validated.

• But he used small samples so we can’t generalise
• And they had a disorder that could act as a confounding variable

Question 21

Research Evaluation 1

Answer 21

Lateralisation of function appears not to stay exactly the same throughout an
individual’s lifetime, but changes with normal ageing.

Across many types of tasks and many brain areas, lateralised patterns found in
younger individuals tend to switch to bilateral patterns in healthy older adults.

Szaflarski et al (2006) 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.

Question 22

Research Evaluation 2

Answer 22

Language may not be restricted to the left hemisphere

Gazzaniga (1998) suggests that some of the early discoveries from split-brain research have been disconfirmed by more recent discoveries.

Damage to the left hemisphere was found to be far more detrimental to language function than was damage to the right.

However, case studies have demonstrated that this was not necessarily the case. One patient, known as J.W., developed the capacity to speak out of the right hemisphere, with the result that J.W. can now speak about information presented to the left or to the right brain

Question 23

Research Evaluation 3

Answer 23

Roland and Pucetti have suggested that the two hemispheres are so functionally different that they represent a form of duality in the brain- that in effect we are
two minds (and that this is a situation that is only emphasised and not caused in the split brain patient).

One legacy of work into lateralisation of function is the growing amount of
pop-psychology literature concerning the functional distinction between the left
and right hemispheres. Such work often oversimplifies and over emphasises the
differences.

Far from working in isolation the two hemispheres form a highly integrated system and are both involved in most every day tasks.