Biopsychology: Split Brain Research Into Hemispheric Lateralisation

Question 1

What Is Hemispheric Lateralisation?

Answer 1

• Some mental processes in the brain are mainly specialised to the left or right hemisphere.
• Language is specialised to the left and visual-motor tasks.

Question 2

What Does Contralateral Mean?

Answer 2

• The opposite side of the body to the brain that controls it.

Question 3

What Is Corpus Callosum?

Answer 3

• Broad band of fibres that joins the two hemisphere of the brain, this allows communication to occur.

Question 4

What Is Split Brain Research?

Answer 4

• A series of studies which began in the 1960s involving epileptic patients who has experienced a surgical separation of hemispheres of the brain by cutting the corpus callosum.
• This allowed researchers to investigate the extent to which brain function is lateralised.

Question 5

Visual Fields And Hemispheres.

Answer 5

1) The information from LVF is processed by the right hemisphere.
2) The information from RVF is processed by the left hemisphere.
3) Language is lateralised to the left hemisphere.
4) The right-hand side of the body is controlled by the left hemisphere.
5) The left-hand side of the body is controlled by the right hemisphere.
6) The cutting of the corpus callosum means that information cannot be passed between the hemisphere.

Question 6

Split Brain Research - Sperry Research Procedure.

Answer 6

• In split brain patients, the corpus callosum has been cut, meaning the two halves cannot communicate to each other; they operate independently.
• Sperry devised a procedure to investigate hemispheric lateralisation.
  Procedure: Individual focuses on central dot which means that information can be presented to either left (processed by the right hemisphere) or the right visual field (processed by the left hemisphere). This means that the information is only processed by one hemisphere and we can see what functions are controlled by each hemisphere.

Question 7

Split Brain Research Findings - Describe What You See.

Answer 7

• The left hemisphere is responsible for speech and language, so when an image is shown to RVF the patient could easily describe what they could see as the information has been processed in the left hemisphere where language is centred.
• When image is shown to LVF they cannot describe what they can see, as there isn’t a language centre in the right hemisphere.
• However if the patient drew the image presented in the LVF then they let the left hemisphere in on the ‘secret’ and then the word can be said.

Question 8

Split Brain Research Findings - Recognition By Touch.

Answer 8

• Split brain patients are unable to say what has been shown in the LVF as the information is processed by right hemisphere which has not language.
• However using their left hand which is controlled by the right hemisphere they can pick out the matching object to the word shown.
• Demonstrates although they cannot say that they have seen anything, they are able to identify the word that is shown in the LVF another way.

Question 9

Split Brain Research Findings - Composite Words.

Answer 9

• If two words are shown simultaneously, one on either side of the visual field e.g Key - Ring the patient would write with their left hand which is controlled by the right hemisphere the word key.
• They would then say the word ring for their speaking left hemisphere so that the left hand would know what to write as the right hemisphere, which controls the left hand is ‘let in on the secret.’

Question 10

Split Brain Research Findings - Recognising Faces.

Answer 10

• The right hemisphere is dominant for recognising faces.
• When asked to match a face with a series of other faces, the picture processed by the right hemisphere (LVF) was consistently selected, whilst the picture presented to the left was consistently ignored.
• When a composite picture made up of two different halves of a face was presented (one to each hem) the left hemisphere dominated in terms of verbal description whereas the right hemisphere dominated in terms of a matching picture.

Question 11

Split Brain Research Into Hemispheric Lateralisation Evaluation: Strength - Involvement In Tasks.

Answer 11

• There is a large amount of evidence to demonstrate lateralised brain functions.
• Sperry and Gazzaniga’s pioneering work into the split-brain phenomenon has produced an impressive and large amount of research findings with a main conclusion that the left hemisphere is more geared towards analytic and verbal tasks whilst the right is more adept to perform spatial tasks and music.
• It is thought that the right can only produce basic words and phrases but contributes emotional and holistic content to language.
• This has led to a key contribution into the understanding of brain processes; the left hemisphere is the analyser whilst the right is the synthesiser.

Question 12

Split Brain Research Into Hemispheric Lateralisation Evaluation: Strength - Strong Methodological.

Answer 12

• There are strengths to the methodology used to research lateralisation.
• The experiments with split-brain patients had highly standardised procedures.
• Patients would be asked to stare at a given ‘fixation point’ whilst one eye was blindfolded.
• The image projected would be flashed for 1/10th of a second meaning the patients would not have time to move their eye across an image so it would not spread across both visual fields.
• This allowed Sperry to vary aspects of the basic procedure and ensured that only one hemisphere was receiving information at a time (high control of variables).
• This meant that Sperry had developed a useful and well controlled procedure.

Question 13

Split Brain Research Into Hemispheric Lateralisation Evaluation: Strength - Theoretical Debate.

Answer 13

• Sperry’s work had prompted theoretical and philosophical debate.
• Some theories for example Pucetti have suggested that the two hemispheres are so functionally different that they represent a form of duality in the brain - we are all two mins and this is emphasised in split-brain patients.
• However, other researchers have argued that the two hemispheres form a high integrated system and both involved in everyday tasks and do not work in isolation.

Question 14

Split Brain Research Into Hemispheric Lateralisation Evaluation: Weakness - Generalisability.

Answer 14

• There are issues with the generalisability of the findings in split-brain research.
• There were only 11 patients who took part in all variations of the basic procedure, all whom had a history of epileptic seizures.
• Some patients had also experienced more disconnection than others through surgery.
• This may have caused unique change in the brain that may have influenced the findings.
• The control group was made up of 11 people with no history of epilepsy which may have been inappropriate.
• This limits the extent to which findings can be generalised to normal brains therefore reducing the validity of the conclsuions.

Question 15

Split Brain Research Into Hemispheric Lateralisation Evaluation: Weakness - Overstated Differences.

Answer 15

• The differences in function may be overstated.
• Although verbal and non-verbal labels can sometimes be applied to summarise differences between the hemisphere, modern neuroscientists would contend that the actual distinction is less clear-cut and messier.
• In the normal brain the two hemisphere are in constant communication and much behaviour typically associated with one hemisphere can be performed by the other when the situation requires it.
• Research into plasticity and functional recovery demonstrates that lateralisation is not always clear or permanent.