Split Research & Hemispheric Lateralisation

Question 1

Hemispheric lateralisation:

Answer 1

The idea that each hemisphere (half) of the brain is mainly responsible
for certain behaviours, processes and activities. This is in contrast with the holistic theory of brain
function, which suggests that function is distributed across the whole brain.

Question 2

Split Brain Research:

Answer 2

Series of studies than began in the 1960s (still ongoing) involving epileptic people who experienced a surgical separation of the hemispheres of the brain. Investigates the extent to which brain function is lateralised.

Question 3

How does vision work?

Answer 3

1. Each visual field has two sides left and right. The right hemisphere controls the left side of the body, and vice versa.
2. In the occipital lobe, nerve impulses are transferred from the retina to the visual cortex via optic nerves.
3. Therefore, information which we receive from the left visual field is processed
   by the right hemisphere, which then coordinates a response to affect the left side of the body.

Question 4

Sperry’s Split Brain Studies:

Answer 4

1. 1968 studies all 11 had undergone a commissurotomy, in which the corpus callosum and other tissues which connect the 2 were cut down the middle.
2. This has been done to control frequent and severe epileptic seizures.
3. The main communication line between the 2 hemispheres was removed.
4. Allowed them to see the extent to which the 2 hemispheres were specialised and whether they were performed independent to each other.

Question 5

Describing what you see:

Answer 5

1. When a picture of an object was shown to an individual’s right visual field, they could easily describe what they see.
2. This is because it was processed by the LH, language centre and the lack of language centres in the RH.
3. If a picture was shown to the LVF, they reported that there was nothing there.
4. In a normal brain, messages from the RH would be relayed to the language centres in the LF.

Question 6

Recognition by touch:

Answer 6

1. Individuals could not attach verbal labels to objects projected in the LVF, but they could select a matching object from a gar-bag of different objects using their left hand.
2. The left hand was also able to select an object that was closely associated with an object.
3. In each case the individuals was not able to verbally identify what they had seen but could nevertheless ‘understand’ what the object was using the RH.

Question 7

Composite words:

Answer 7

1. If 2 words were presented simultaneously, one on either side of the visual field.
2. For example, ‘key’ on the left and ‘ring’ on the right.
3. The individual would select a key with their left hand (the LVF goes to the right hemisphere linked to left hand) and say the word ‘ring’

Question 8

Matching faces:

Answer 8

1. The RH also appeared dominant in terms of recognising faces.
2. When asked to match a face from a series of other faces the picture processed by the RH (LVF) was consistently selected, whilst the picture presented to the LH was consistently ignored.
3. When a composite picture made up of two halves of a face was presented- one half to each hemisphere- the LH dominated in terms of verbal description whereas the RH dominated in terms of selecting a matching picture.

Question 9

E: Demonstrated lateralised brain functions (HL)

Answer 9

1. Sperry’s pioneering work and Gazzaniga’s later work into the split-brain phenomenon has produced a sizeable body of research findings.
2. The main conclusion of which appears to be the left hemisphere is more geared towards analytic and verbal tasks, the right is more adept at spatial tasks and music.
3. The RH can only produce rudimentary words and phrases but contributes emotional and holistic content to language.
4. Research shows that the left hemisphere is the analyser whilst the right hemisphere is the synthesiser, a key contribution to our understanding of brain processes.

Question 10

E: Brain Scans (HL)

Answer 10

1. Fink et al (1996) used PET scans to identify which brain areas were active during a visual processing task.
2. When participants were asked to assess the picture as a whole, regions of the RH were more active.
3. When required to focus in on the finer details the areas of the LH tend to dominate.
4. As far as visual processing is concerned, hemispheric lateralisation is a feature of the connected brain and the split brain.

Question 11

E: Strengths of the methodology (SB)

Answer 11

1. Experiments involved highly specialised and standardised procedures.
2. Pps would be asked to stare at the ‘fixation point’ and an image would be projected for 1/10 of a second.
3. This meant that the split-brain individuals would not have time to move their eye across the image and spread the information across both sides of the brain.
4. This allowed Sperry to vary aspects of the basic procedure and ensured that only one hemisphere received information.

Question 12

E: Jared Nielsen et al. 2013 (HL)

Answer 12

1. One limitation is that the LH as analyser and RH as sythesiser may be wrong.
2. There may be different functions in the RH and LH, but research suggests people do not have a dominant side of their brain which creates a different personality.
3. Jared Nielsen et al. (2013) analysed brain scans from over 1000 people aged 7-29 and did find that people used certain hemispheres for certain tasks.
4. But there was no evidence of a dominant side, no mathematician’s brain.
5. Notion of right or left brained people is wrong.

Question 13

E: Generalisation Issues (SB)

Answer 13

1. Causal relationships are hard to establish.
2. The behaviour of Sperry’s split-brain participants was compared to a neurotypical control group- none had epilepsy.
3. Major confounding variable. Any differences that were observed between the two groups the result of the epilepsy rather than the split-brain.
4. This means that some of the unique features of the split-brain participants’ cognitive abilities might have been due to their epilepsy.