Split-brain research

Split-brain research

A series of studies involving people with epilepsy who had experienced a surgical separation of the hemispheres of their brain to reduce the severity of their epilepsy.

Enabled researchers to test lateral functions of the brain in isolation

Sperry split-brain PROCEDURE

11 people who had a split-brain operation

Natural experiment - IV happens naturally (having the operation)

Used a setup where an image could be projected to RVF or LVF.

In neurotypical brains the corpus callosum would share the information between both hemispheres. But presenting the image to 1 hemisphere of a split-brain participant meant that information cannot be conveyed from 1 hemisphere to the other.

Sperry split-brain FINDINGS

When an image was shown to the RVF (linked to LH), the participant could describe what they saw.

If an image was shown to the LVF (linked to RH), they said there was nothing there.

In a connected brain messages from the RH are relayed to the language centres in the LH but this isn’t possible in split-brains.

Although they couldn’t give verbal labels to images shown to the LVF, they could select a matching object out of sight using their left hand (linked to RH)

The left hand could select an object that was more closely associated with an image presented to the LVF.

If a pin-up picture was shown to the LVF there was an emotional reaction but they reported seeing nothing or a flash of light

Sperry split-brain CONCLUSIONS

These observations show how certain functions are lateralised in the brain and supports the view that the LH is verbal and the RH is more emotional

S Research support

Luck

Split-brain participants perform better than connected controls at certain tasks. They were faster than controls at identifying the odd one out in a set of similar objects.

The LH’s better cognitive strategies are watered down by the RH in connected brains.

Supports Sperry’s earlier findings that the left brain and right brain are distinct

S Standardised procedures

Ensured that the information presented to participants was only for 1/10 of a second to 1 visual field so it could only be processed by 1 hemisphere. The other eye was also blindfolded to prevent it being picked up by both eyes.

Made it easier to make comparisons about the functioning of both hemispheres.

Increases replicability and reliability. Valid conclusions can be drawn so increases validity

W Generalisation issues

The behaviour of the participants was compared to a neurotypical control group but none of them had epilepsy which is a big extraneous variable.

Observed differences may be due to epilepsy rather than the split-brain

Suggests that some unique cognitive abilities may have been due to their epilepsy.

W Ethics

The operation wasn’t done for the purpose of the research.

Patients are having information flashed at them and highlights shortcomings.

Testing took place over a lot of time (maybe for years) and may have been stressful

Trauma of the operation may mean that the participants don’t fully understand what they agreed to