Sperry - Hemisphere Deconnection and Unity in conscious awareness

Question 1

Background to the Sperry study

Answer 1

1. Some patients with severe epilepsy who had not responded to treatment were offered surgery to help reduce their seizures
2. The surgery involved cutting down the corpus callosum to disconnect the right and left hemispheres
3. These patients reported very few obvious effects of the surgery other than a reduction in symptoms of their epilepsy
4. Research seemed to suggest that without a corpus callosum, the left and right hemispheres of the brain worked like two separate brains (split-brain) instead of one whole brain

Question 2

Aim to sperry

Answer 2

1. In 1968, Roger Sperry studied what effects could be seen in these patients by monitoring how they processed information using their “split-brain”
2. He was interested to see how the split-brain worked compared to a normal brain

Question 3

Procedure to sperry

Answer 3

1. Sperry studied a group of 11 participants who had their corpus callosum cut
2. They were each given various tasks to test how they processed different types of information in the split-brain
3. One of the most well known tests used by Sperry was a visual task where participants focused on the centre of a screen on which information was presented to the left and right side of the visual fields at the same time
4. Two different words or pictures were presented - one on the left of the mid-point and one on the right
5. This means that the left side of each eye would pick up one image (the one on the right of centre) while the right side of each eye would pick up the other image (the one on the left of centre)
6. The information on the right of the visual field would be passed to the left hemisphere, while information on the left of the visual field would be passed to the right hemisphere. The participants were then asked to say the word or pictures they had seen on the screen
7. On some occasions, rather than say the word or identify the picture, the participants would be asked to point to an item or picture
8. They would be shown a variety of objects or pictures including the one they had just been shown. They would identify what they had seen using either the same hand or the opposite hand
9. Other variations of this task included putting unseen objects into one of the hands and asking them to identify them from touch along, and placing different objects in each hand and then asking them to feel for them in a large pile of different objects
10. All of these tasks involved the same basic process - sending different types of sensory information to the left and right hemispheres, and then asking the brain to respond to the information using either the same or the opposite hemisphere.

Question 4

Results to sperry (tasks involving reading words or selecting objects)

Answer 4

1. When words were shown to the right visual field, the patients had no problem repeating the word back to the researcher
2. However when words were shown to the left visual field (sent to the right hemisphere) patients had trouble saying what they had seen - because the broca’s region is in the left hemisphere
3. If a word of picture was shown to the left visual field, the participants had little trouble selecting an object that matched what they had seen.
4. When the word or picture was shown to the right visual field (left hemisphere), the participants struggled to point to the correct objects

Question 5

Results to sperry (tasks involving objects presented to each hand)

Answer 5

1. When objects were felt by the right hand (so passed to the left hemisphere) they could name the object
2. When objects were felt by the left hand, they found it more difficult to say what they could feel
3. When two different objects were given to the participant - one in each hand - and after they were asked to feel around in a pile of objects for the two objects, they could identify each item with the hand that originally held it. If the opposite hand picked up the item, they could not identify it as the item they had held before

Question 6

Conclusion to the sperry study

Answer 6

1. Sperry suggested that each hemisphere is capable of working perfectly well without being connected to the other side
2. However, each hemisphere seems to have its own memories, which without a corpus callosum, could not be shared with the other side
3. This caused problems for some activities, supporting the idea that the right and left hemispheres have different roles
4. The left hemisphere seemed to be better at naming items using words when they had been held by the right hand
5. However the right hemisphere was better at identifying objects by feeling for them with the left hand after previously being held by the left hand
6. This supports the idea that the left hemisphere controls more language abilities but the right hemisphere controls spatial abilities

Question 7

Strengths of the sperry study

Answer 7

1. Sperry gathered a lot of detailed information, improving the reliability of the study
2. Another strength is that he designed procedures (such as the split screen for presenting visual information) that could be kept the same for each participant. This makes the data reliable way and each participant’s results can be compared more easily

Question 8

Weakness of the sperry study

Answer 8

1. A weakness of Sperry’s study is that the sample of 11 participants is too small to be able to generalise the results very confidently. Very few people have surgery to sever the corpus callosum so the results might not be that useful for explaining how normal brains work
2. The tasks Sperry had the participants do in the laboratory may be very artificial. It is not often you will be asked to look at a picture with one eye and then point to the same picture with your hands so the results may lack ecological validity