topic 4 - Sperry (1968) Hemisphere Deconnection and Unity Flashcards
what was the background to the study?
some patients with severe epilepsy who have not responded to treatment were offered surgery to help reduce their seizures. The surgery involved cutting down their corpus callosum to disconnect/ separate the hemispheres. These patients reported very few obvious effects of the surgery other than the reduction of symptoms of epilepsy. Research suggested that when cutting the corpus callosum, the two hemispheres worked as two separate brains (split brain) instead of a whole brain.
what was the aim?
the aim was to see how the split-brain worked in comparison to a normal brain.
what was the procedure?
first, Sperry studied a group of 11 participants who had their corpus callosum cut. They were each given various tasks to test how they processed different types of information in the ‘split-brain’.
the test was a well-known test used by Sperry which 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. Two different worlds or pictures were presented- one on the left of the mid-point and one on the right. This means that the left side of each eye would pick up the image, while the right side of each eye would pick up the other image.
The information on the right visual field (RVS) would be passed to the left hemisphere, while the information on the left visual field (LVS) would be passed to the right hemisphere. The participants are then asked to say the word/s or picture/s , that they had seen on the screen/.
On some occasions rather than say the word(s) or identify the picture(s), the participants would be asked to point to an item or picture. They would be shown a variety of objects or pictures including the one they had just been shown. They would then identify what they had seen using either the same hand or the hand of the opposite side of the body.
Other variations of this task include putting unseen objects into one of the hands and asking them to identify them from touch alone and placing different objects in each hand and then asking them to feel for them in a large pile of different objects.
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 opposite hemisphere.
what were the results?
results from the task involve reading words or selecting objects were seen to be different:
- when words were shown to the RVS, the patients had no problem repeating the word back to the researcher. However, when words were shown to the LVS, patients had trouble saying what they had seen.
- if a word or picture was shown to the LVS, the participants had little trouble selecting an object that matched what they had seen. When the word or picture was shown to the RVS, the participants found it difficult to point out the correct object.
similar results were found when objects were presented in each hand:
- when words were felt by the right hand, they could name the object. When an object was felt by the left hand they found it difficult to say what they feel.
- when two different objects were given to the participant ,one in each hand and after they were asked to feel around a pile of object to find the two objects. They could only identify each item with the hand that originally held it. If the opposite hand picked up the object, they could not identify the item they held before.
what was the conclusion?
Sperry concluded that each hemisphere is capable of working perfectly well without being connected to other side, however, each hemisphere seems to have it’s own memories, which, without, a corpus callosum, could not be shares with the other side. This caused problems for some activities , supporting the idea that the right and left hemispheres have different roles. The left hemisphere seemed to be better at naming items using words when they had been held by the right hand. 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. This supports the idea that the left hemisphere controls more language abilities but the right hemisphere controls spatial abilities.
what was the strength of the study?
the strength of the study is Sperry gathered a lot of detailed information, improving the reliability of his study.
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 means that the data was gathered in a reliable way and each participants results can be compared more easily.
what was the weakness of the study?
A weakness is the sample size is too small. There were only 11 participants who took part in the study which means it is too difficult to generalise the results very confidently. Also, very few people go through the surgery where the corpus callosum is cut. So the results might not be useful for explaining how ‘normal brains’ work.
Another weakness is that 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. This means the results lack ecological validity.
