Hemispheric Lateralisation

Question 1

What is the left hemisphere (right body) responsible for?

Answer 1

• Math/scientific skills
• Analytic
• Written/spoken language

Question 2

What is the right hemisphere (left body) responsible for?

Answer 2

• 3-D Shapes
• Creativity
• Emotion
• Facial Recognition

Question 3

What are spatial relationships?

Answer 3

The right hemisphere also appears to be dominant for spatial functions like finding your way and people with damage to the right hemisphere may have difficulties with spatial tasks such as remembering a route

Question 4

What is Broca’s area?

Answer 4

• Language center in the back portion of the frontal lobe of the left hemisphere
• Broca found that patients with damage to the Broca’s area could understand language but not speak or write

Question 5

What is Wernicke’s area

Answer 5

• Language center in the posterior portion of the left temporal lobe
• Wernicke found that patients with damage to the Wernicke’s area could speak but were not able to understand language

Question 6

Positive evaluation of hemispheric lateralisation? - research to support case studies

Answer 6

Research support comes from case studies on patients with damage to Broca’s and Wernicke’s areas that have demonstrated their functions being lateralised in the left hemisphere. For example, the case study of Tan who could not produce language to due to damage in this left hemisphere specifically in the. Broca’s aphasia is an impaired ability to produce language; in most cases, this is caused by brain damage in Broca’s areas as demonstrated by. This evidence demonstrates the important role played by this particular brain region in the comprehension of language.

Question 7

Positive evaluation of hemispheric lateralisation - reliable research to support

Answer 7

However, there is reliable research support from human clinical case studies of the loss of specific abilities after restricted brain damage to a particular region or hemisphere e.g. receptive aphasia (language disorder where there is difficulty understanding spoken language) following damage to Wernicke’s area is seen in many cases. This suggests that some functions of the brain are localised (found in a particular region) and lateralised ( in one half of the brain) at least in part.

Question 8

Negative evaluation of hemispheric lateralisation - Case studies

Answer 8

However, as much research support into Wernicke’s and Broca’s areas comes from case study evidence. These case studies investigate the effect of damage in specific individuals and the effects on their individual cognitive functions such as patient Tan who had Broca’s aphasia. However, these effects may be specific to the individuals concerned and their results may not be generalisable to others. This means results from case studies can limit our full understanding if these language areas.

Question 9

Negative evaluation of hemispheric lateralisation - reductionist

Answer 9

Also, critics argue that theories of lateralisation are biologically reductionist in nature and try to reduce very complex human behaviours and cognitive processes to one specific brain region. For example, there is no evidence for 100% left hemisphere dominance for language, as it is 96% in right handers and only 70% in left handers. Therefore, such critics suggest that a more thorough understanding of the brain using a more holistic approach is required to truly understand complex cognitive processes like language.

Question 10

Negative evaluation of hemispheric lateralisation - post mortem studies

Answer 10

Another problem is that much of the evidence for Wernicke’s & Broca’s areas comes from post-mortem studies which investigate the brain after death. Although this may help to pinpoint areas of the brain involved in different functions, it is not possible to then refine the understanding of these functions by getting the participant to do further tasks. This means that more modern methods of brain imaging on live patients might reveal more accurate information.

Question 11

What is a split brain patient?

Answer 11

Split brain patients are those who have had the connection between left and right hemisphere severed. In other words, the corpus callosum has been cut. This may be done in cases of severe epilepsy to restrict the epileptic seizures to only one hemisphere and reducing the severity of the attack. Normally the two hemispheres share information.

Question 12

What processes are involved in split brain research?

Answer 12

• Split visual field experiments
• Participants are sat in front of a screen and asked to gaze at a fixed point in the centre of a screen
• Visual stimuli are projected onto the screen either to the right or left visual field at a very high speed, so the participant has no chance to move their head and is only able to process the image in the visual field where it was placed

Question 13

Testing, finding and suggestion from research where words were projected to the left visual field (LVF) so going to the right hemisphere.

Answer 13

Verbal responses to language. The words did not seem to be registered. Pt’s would say they had not seen anything Suggests that the left hemisphere is responsible for language (so words need to be presented to the RVF in order to be registered)

Question 14

Testing, finding and suggestion from research where A word (e.g., fork) was projected to LVF (goes to right hemisphere). Left hand (controlled by right hemisphere) was placed behind a screen and then had to select the object from several items.

Answer 14

Physical responses to language Pt’s could select the correct object despite being unable to verbally report having seen it. Indicates that the right hemisphere does have some language ability for understanding words if not for speech

Question 15

Testing, finding and suggestion from research where A different face was presented to each hemisphere at the same time. Pt’s were then given a set of faces to look at and asked to select those that they had seen earlier

Answer 15

Matching abilities in response to pictures Visuospatial processing.Pt’s chose the one presented to the right hemisphere indicating its role in identifying faces and shapes. Indicated that the right hemisphere is responsible for visuospatial tasks

Question 16

Positive evaluation of split brain research - practical applications

Answer 16

A strength of split-brain research is that it has useful practical applications enabling a greater understanding of the differing functions of the hemispheres and adding to the unity of the consciousness debate. For instance, we now know that language is largely processed in the left hemisphere. This allows our scientific understanding of the brain to move forward from split brain research

Question 17

Positive evaluation of split brain research - methodological strength

Answer 17

One strength of Sperry’s research into the split-brain phenomena is that it has methodological strength. For example, the experiments involving split-brain patients were highly specialised and used standardised procedures. This is a strength because the standardisation of presenting visual info to one hemisphere at a time could be controlled so well that Sperry was able to vary aspects of the basic procedure very easily (ensuring only one hemisphere was receiving info), but still maintaining a high level of control. As a result, Sperry’s research into the split-brain phenomena has high internal validity and therefore has high credibility

Question 18

Negative evaluation of split brain research - lacks generalisability

Answer 18

The split-brain research lacks generalisability as there was a limited number of participants (only 10-15 have been subjected to systematic study). In addition, the Pt’s varied considerably in age, gender and handedness as well as the age at which they developed epilepsy and the degree of drug therapy they had experienced before their surgery. All factors that will affect behaviour. This implies split brain research may provide results that we cannot apply to understand all people with split brain and the lateralisation of brain function

Question 19

Negative evaluation of split brain research - cause and effect

Answer 19

2. The split-brain patients were often compared to neurotypical controls (typical people with no conditions), but these people often had no history of epilepsy either (i.e., not matched pairs) and therefore this could be a potential confounding variable as a history of epilepsy would affect general behaviour. This means it is harder to establish cause and effect and there could be other explanations for split brain findings, such as the epilepsy itself causing changes in the brain that influenced the findings. It is also the case that some PPs had experienced more disconnection of the two hemispheres so again this was not controlled for.