BIO 08 (part b) - Split-brain research

Question 1

What is split-brain research

Answer 1

• A series of studies which began in the 1960s (and are still ongoing) involving people with epilepsy who had experienced a surgical separation of the hemispheres of their brain (by cutting the corpus callosum down the middle) to reduce the severity of their epilepsy
• This enabled researchers to test lateral functions of the brain in isolation

Question 2

Who conducted split-brain research?

Answer 2

Roger Sperry

Question 3

What was the procedure of Sperry’s research?

Answer 3

• Eleven people who had a split-brain operation were studied using a special set up in which an image could be projected to a participant’s RVF (processed by the LH) and the same, or different, image could be projected to the LVF (processed by the RH)
• In the ‘normal’ brain, the corpus callosum would immediately share the information between both hemispheres giving a complete picture of the visual world
• However, presenting the image to one hemisphere of a split-brain participant meant that the information cannot be conveyed from that hemisphere to the other

Question 4

What were the findings of Sperry’s research?

Answer 4

• When a picture of an object was shown to a participant’s RVF (linked to LH), the participant could describe what was seen
• But they could not do this if the object was shown to the LVF (RH) - they said there was ‘nothing there’
• This is because, in the connected brain, messages from the RH are relayed to the language centres in the LH, but this is not possible in the split-brain
• Although participants could not give verbal labels to objects projected to the LVF, they could select a matching object out of sight using their left hand (linked to RH)
• The left hand was also able to select an object that was most closely associated with an object presented to the LVF (for instance, an ashtray was selected in response to a picture of a cigarette)
• If a pinup picture was shown to the LVF there was an emotional reaction (e.g. a giggle) but the participants usually reported seeing nothing or just a flash of light

Question 5

What was the conclusion of Sperry’s research?

Answer 5

These observations show how certain functions are lateralised in the brain and support the view that the LH is verbal, and the RH is ‘silent’ but emotional

Question 6

What are the strengths of Sperry’s research?

Answer 6

• Research support from recent split-brain research
• Scientific procedure
• Quite ethical
• Enabled discoveries

Question 7

What support is there from recent split-brain research?

Answer 7

• One strength is support from more recent split-brain research
• Michael Gazzaniga (Luck et al. 1989) showed that split-brain participants actually perform better than connected controls on certain tasks
• For example, they were faster at identifying the odd one out in an array of similar objects than normal controls. In the normal brain, the LH’s better cognitive strategies are ‘watered down’ by the inferior RH (Kingstone et al. 1995)
• This supports Sperry’s earlier findings that the ‘left brain’ and ‘right brain’ are distinct

Question 8

How does Sperry’s research use a scientific procedure?

Answer 8

• Has reasonably good control over variables
• It is the only way that lateralisation can be studied experimentally

Question 9

How is Sperry’s research quite ethical?

Answer 9

• The split-brain operation was not performed for the purpose of research, so, in that sense, Sperry’s participants were not deliberately harmed
• In addition, all procedures were explained to the split-brain participants and their full informed consent was obtained

Question 10

How did Sperry’s research enable discoveries?

Answer 10

Split-brain research has enabled discoveries of lateralisation of function

Question 11

What are the limitations of Sperry’s research?

Answer 11

• Generalisation issues
• Some ethical issues
• Oversimplifies hemispheric lateralisation

Question 12

How does Sperry’s research have generalisation issues?

Answer 12

• One limitation of Sperry’s research is that causal relationships are hard to establish
• The behaviour of Sperry’s split-brain participants was compared to a neurotypical control group
• An issue though is that none of the participants in the control group had epilepsy
• This is a major confounding variable
• Any differences that were observed between the two groups may be the result of the epilepsy rather than the split brain
• In addition, they used a small sample of 11 which is unrepresentative
• This means that some of the unique features of the split-brain participants’ cognitive abilities might have been due to their epilepsy (though Fink’s research, above, supports Sperry’s conclusions)

Question 13

What are some ethical issues of Sperry’s research?

Answer 13

• One limitation of Sperry’s research is that there are some ethical issues
• The trauma of the operation might mean that the participants did not later fully understand the implications of what they had agreed to
• They were subject to repeated testing over a lengthy period (years in some cases) and this may have been stressful over time

Question 14

How does Sperry’s research oversimplify hemispheric lateralisation?

Answer 14

• One limitation of Sperry’s research is that it oversimplifies hemispheric lateralisation
• Usually hemispheres are constantly communicating, and plasticity allows for compensation across hemispheres