Hemispheric laterlisation: split brain research

Question 1

What is hemispheric lateralisation?

Answer 1

The idea that the two halves of the brain are different and certain processes and functions are controlled by one hemisphere rather than the other.

Question 2

What does the right side of the brain process?

Answer 2

The RIGHT side of the brain processes info from LEFT half of body (e.g visual info from the left eye)

Question 3

What does the left side of the brain process?

Answer 3

The LEFT side of brain processes info from RIGHT half of body (e.g visual info from the right eye)

Question 4

What is usually processed by the left hemisphere?

Answer 4

Language. Broca’s area is in the left frontal lobe and Wernicke’s area is in the left temporal lobe.

Question 5

What is usually processed by the right hemisphere?

Answer 5

The right hemisphere seems to have more involvement in the processing of faces and emotion on faces.

This was supported by studies into the split brain patients.

Question 6

What are the 2 hemispheres connected by?

Answer 6

The corpus callosum

Question 7

What is the corpus callosum?

Answer 7

A bundle of nerves

Question 8

Why do some people have ‘split brains’?

Answer 8

‘Split brain’ research is on people who have two separated hemispheres of their brain (left and right).
This occurred because of serious epilepsy.
Epilepsy is sometimes caused by scar tissue in the brain. Sometimes this can be safely surgically removed.
But sometimes the cause is not observable or the scar tissue cannot be removed.

Question 9

What is the operation to remove the epilepsy called?

Answer 9

a commissurotomy

Question 10

What did the surgery involve?

Answer 10

Cutting the corpus callosum.
The electrical discharge of epilepsy cannot move across to the whole brain when this is cut.

Question 11

What is the result of the surgery?

Answer 11

Patients had 2 separate brain hemispheres that could no longer communicate through the corpus callosum - they now had a ‘split brain’.

This was done to control frequent and severe epileptic fits.

Question 12

What did Sperry want to do?

Answer 12

Study the effects of this in order to investigate whether the 2 hemispheres were specialised to the point they operated independently of each other.

Studied these split brain patients and compared them to patients with no hemisphere separation. Devised a system to study how 2 separated hemispheres deal with, for example, speech and vision.

Question 13

Describe Sperry’s procedure

Answer 13

Sperry devised a procedure where a word or picture is projected into the left or right visual field.
This is then dealt with by the opposite hemisphere of the brain and the information isn’t shared between the two hemispheres.

Question 14

Describe Sperry’s procedure (more detailed)

Answer 14

• Split brain patients would have an image projected to their right visual field (processed by their left hemisphere) or a different image projected to the left visual field (processed by the right hemisphere).
• Presenting the image to one hemisphere of a split-brain patient meant the information would only be perceived by one hemisphere (due to the corpus callosum surgery).

Question 15

What was the method called?

Answer 15

the divided field

Question 16

Why was the method called this?

Answer 16

This is because the ppts would look ahead and see one item to the left (of their visual field) and one item to the right (of their visual field)

Question 17

What experiment was used?

Answer 17

The method used was a quasi-experiment, as it involved comparing the performance of the 11 participants on various tasks with the performance of people with no inter-hemisphere deconnection.

This is a quasi-experiment because the IV is an internal characteristic of the ppt.

Question 18

What was the independent variable?

Answer 18

The independent variable was therefore the whether a person had hemisphere deconnection or not

Question 19

What was the dependent variable?

Answer 19

the dependent variable was the participants performance on the tasks.

Question 20

What were Sperry’s findings?

Answer 20

• ppts could only describe what they saw when it was shown to their left hemisphere (which contains both language centres), not to their right hemisphere.
• this was also true for held items - a patient touching an item with their left hand couldn’t describe it (as this information goes to the somatosensory cortex in the right hemisphere - which does not have the language centres).
• When doing a task involving matching faces to pictures, the right hemisphere was dominant for this (higher accuracy when faces shown on left visual field to right hemisphere). This shows that facial recognition is lateralised to the right hemisphere.

Question 21

Explain Sperry’s findings in detail

Answer 21

When a picture of an object was shown to a participant’s right visual field (linked to the left hemisphere), the ppt could describe what was seen but they couldn’t do this if the object was shown to the left visual field (linked to the right hemisphere) - they said there was ‘nothing there’. This is because, in the connected brain, messages from the right hemisphere are relayed to the language centres in the left hemisphere but this is not possible in the split brain.

Although ppts couldn’t give verbal labels to objects projected by the left visual field, they could select a matching object out of sight using their left hand (linked to right hemisphere). The left hand was also able to select an object that most closely associated with an object presented to the left visual field e.g. an ashtray was selected in response to a picture of a cigarette.

If a pinup picture was shown to the left visual field there was an emotional reaction such as a giggle but the ppts usually reported seeing nothing or just a flash of light.

Question 22

What were Sperry’s conclusions?

Answer 22

These observations show how certain functions are lateralised in the brain and support the view that the left hemisphere ins verbal and the right hemisphere is ‘silent’ but emotional.

Question 23

Give one limitation of the procedure

Answer 23

People naturally move their eyes toward stimulus so the ppts will end up seeing a stimulus with both sides of their eyes

Question 24

Why is this a problem?

Answer 24

Both hemispheres will see the stimulus. This ruins the experiment because you’re not studying them working separately (a ‘split’ brain)

Question 25

What is the solution?

Answer 25

He showed the stimulus for 1/5 of a second (200 milliseconds). This meant the ppt did not have time to move their eyes towards it
This meant Sperry could only present single words or pictures