Lateralisation Of Function In The Brain

Question 1

Hemispheric lateralisation

Answer 1

This is the idea that the two halves of the brain are functionally different, and that each hemisphere has functional specialisation

Question 2

Split- brain research

Answer 2

This is research on people who have had their brain split in half, through the severing of their corpus collosum

Question 3

Left hemisphere specialisation

Answer 3

• controls the right side of the body
• language
• analytical tasks
• views objects in right visual field

Question 4

Right hemisphere specialisation

Answer 4

• controls the left side of the body
• music
• drawing
• facial recognition
• spatial tasks
• emotional content of language
• views objects through left visual field

Question 5

Evidence for lateralisation of function (language)

Answer 5

• there is evidence to suggest the left hemisphere is specialised for language. In about 95% of right-handed people, language is specialised in their left hemisphere. In about 70% of left-handed people, the right hemisphere is dominant (however it is important to note that only 10% of the population are left-handed). The remaining people either have either right hemisphere dominant or neither hemisphere is dominant.
• the Wada test provides evidence for the lateralisation of language. This involves injecting anaesthesia to anaesthetise one hemisphere. The participant them reads aloud. When the left hemisphere was anaesthetised, reading aloud is disrupted in more than 90% of people.
• Aphasia (impaired linguistic abilities) occurs more as a result of damage to the left hemisphere than the right hemisphere.

Question 6

Evidence for lateralisation of function (emotion)

Answer 6

• there is evidence that the right hemisphere is dominant for emotion.
• Sperry completed an experiment whereby he very quickly presented a photograph of a naked person to a split-brain patients left visual field (therefore the right hemisphere will process it). The patients reported that they saw nothing. However, they did smile, blush and giggle- even though they did not know why.
• Gianotti found that patients who had damage to their left hemisphere became more aggressive and anxious. However, patients with damage to their right hemisphere became unemotional. This suggests that emotion is lateralised in the right hemisphere more than in the left.

Question 7

Evaluation of using split-brain patients to investigate hemispheric lateralisation of function

Answer 7

• the disconnections between the hemispheres was greater in some patients than others
• the comparison groups were not considered to be valid as they were often people with no history of epileptic seizures
• the data was artificially produced as in real life a severed corpus collosum can be compensated for by the unrestricted use of two eyes.
• sample sizes used are minimal and do not account for individual differences to the general population, therefore lack generalisability.

Question 8

Lotta’s grandam suffered a stroke to the left hemisphere, damaging Broca’s area and the motor cortex. Describe the problems that Lotta’s grandma is likely to experience

Answer 8

• as a consequence of damage to Broca’s area, she will suffer language/speech problems (Broca’s aphasia)
• her speech production will be affected (but not her understanding)
• she will only be able to talk in short meaningful sentences
• her speech will lack fluency/difficulty with certain words which help sentence function
• as a consequence of damage to the motor cortex, she will likely suffer from loss of muscle function. This will only be in the right side of the body as she damaged the left hemisphere

Question 9

Sperry- effects of split brain research

Answer 9

Method:
- 11 participants had undergone split brain surgery as a result of epilepsy that couldn’t be controlled by medication. A control group was used who had no hemispheric disconnection
- In one of the experiments, participants covered one eye and looked at a fixed point on a projection screen. Pictures were projected onto the right or left of the screen at high speeds so that there was no time for eye movement

Results:
- If the picture was shown in the right visual field, all of the participants could say or write what it was without a problem. But if the image was flashed onto the left, the split brain participants couldn’t say or write what they’d seen. They could however select a corresponding object with their left hand which represented what had been shown to their left eye (right hemisphere), even though they didn’t know why they had selected this object

Conclusion:
- This shows that different area of the brain specialise in different function. The left hemisphere can convert sight into spoken and written language.
- Usually information entering the right hemisphere can cross over to be processed in the left. As the results show, this can’t happen in split brains, so the information going to the right hemisphere can’t be converted into language at all. However, the right hemisphere can still produce a non-verbal response.

Evaluation:
- The study only used 11 participants, which is a very small sample size for being able to generalise to others.
- Epilepsy is usually cause by brain damage and the patients had also been on medication which may have affected their brains. Therefore, it is hard to conclude that the ways they process information would be the same as for people without epilepsy or split brain treatment
- Lack ecological validity