streda 20. februára 2013

Sperry and Gazzaniga: The Split Brain Study

1. What does it mean for a person's brain to be "split
2. What was the reason why this procedure was performed on patients?
3. Explain one of the tests Sperry and Gazzaniga performed on these split brain patients.
4. What were the results of this test?
5. What is the reason that these results occurred?
6. What is the corpus callosum and what role does it serve in your brain?

1. Each hemisphere is still able to learn after the split brain operation but one hemisphere has no idea about what the other hemisphere has experienced or learned. Today, new methods and technology in split brain operation make it possible to cut off only a tiny portion and not the whole of the corpus callosum of patients.

2. The experiments were undertaken on people who had already had their corpus callosum severed as treatment for severe epilepsy in the 1960s. Epilepsy is a kind of storm in the brain, which is caused by the excessive signaling of nerve cells, and in these patients, the brain storm was prevented from spreading to the other hemisphere when the corpus callosum was cut off. This made it possible for the patients to live a normal life after the operation

3. The participants were 11 ‘split-brain’ patients. The participants had all undergone hemisphere deconnection because they had a history of advanced epilepsy which could not be controlled by medication.
The method used was a natural experiment called also quasi-experiment. These experiments involved comparing the performance of the 11 participants on various tasks with the performance of people with no inter-hemisphere deconnection. The independent variable was therefore the whether a person had hemisphere deconnection or not and the dependent variable was the participants performance on the tasks.
Sperry used a number of ingenious tasks in order to investigate lateralisation of brain function. The tasks were carried out in laboratory conditions, using specialised equipment and were highly standardised. The task all involved setting task separately to the two hemispheres.
The tasks used to send information to just one hemisphere involved asking patients to respond to tactile information. This involved presenting a stimulus to one of the hands of a split-brain patient so the participant could not see the stimulus and then asking the participant to name it. If the stimulus is presented to the participant’s left hand the participant should not be able to name it.
It is also possible to present Auditory (sound) and olfactory (smell) stimuli to one side of the brain using various methods of blocking the unused ear or nostril.

4.When participants were presented with an image in one half of their visual field and then presented with the same image in the other half of the visual field they responded as if they had never seen the image before. If the same image was presented in the original visual field the participants were able to recognise the image as one they had seen before.
Participants were not able to give a description of an image that was presented to the left hand side of the visual field. The image was either not noticed or just appeared as a flash. But they could respond non-verbally by pointing with their left hand to a matching picture or selecting an object presented among a collection of other pictures and objects. This works only with right-handed participants.
If two symbols were presented simultaneously, one on either side of the visual field for example a dollar sign on the left and a question mark on the right hand and the participant was required to draw with their left-hand what they had seen, they would draw the left visual field symbol a dollar sign. If they were required to say what they had just drawn, the participant would say by name, the right visual field symbol a question mark.
Objects put in the participants hand for identification by touch could be described or named in speech or writing if they were in the right hand but if placed in the left hand, the participant could either only make wild guesses or even appeared to be unaware that anything at all was present. However, if the object was taken from the left hand and placed in a ‘grab bag’, or was scrambled among other test items, the participant was able to search out and retrieve it with their left hand.
Sperry showed that split-brain patients were better at completing highly unusual tasks that this would have no advantage in the real world.
Through the case studies Sperry found that the hemisphere deconnection did not appear to affect the patients’ intelligence (as measured by an IQ test) or their personality. The effects of the surgery did seem to have affected the patients in that they had short-term memory deficits, limited concentration spans and orientation problems.

5. Research showed that split brain patients present superiority on the right hemisphere when it comes to spatial tasks, such as arranging blocks. Researchers also showed drawings to the left and right hemispheres and the patient was asked to draw what he saw from both hemispheres. The conclusions were that the left-handed drawings were better drawn.

6. Corpus callosum is a type of epilepsy which is caused by the excessive signaling of nerve cells. By cutting the corpus callosum which connects the two cerebral hemispheres the brain storm was prevented from spreading to the other hemisphere.

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