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Sperry

Terms in this set (27)

Background
-The left hemisphere has the ability to control language this was found out in the 19th century through the work of Brocca and Wernicke.
-->Broca- patient could understand language but could only say 'tan' autopsy showed damage in the left frontal lobe.
-->Wernicke- patient couldn't understand simple questions but could speak fluently damage in the left temporal lobe.
-When studies were published their was no way of checking it in alive people.
-In 1940s the commissurotomy me was developed to cut the corpus callosum in cases of severe epilepsy.
-In 1950s Sperry came up with that tachistoscope which allowed research into exploring the different sides of the brain.
Aims
To study the functions of separated and independent hemispheres, specifically to see the effects of the hemisphere de-connection in split brain patients who have had their corpus callosum severed.
Research methods
- Case study/Quasi
- 11 participants studied --> 2 in depth.
Sample
- 11 people who had already undergone surgery (commisotory) to sever their corpus callosum due to severe epilepsy.
- The performance of this group was compared with a group of people with no into-hemisphere de-connection.
Sampling method
OPPITUNITY
IV
Whether the participants had had their corpus callosum cut due to a commisorotomy.
DV
How well participants perform in their tests (visual and tactile).
CV
- Same equipment --> Tachistoscope.
- Screen on the tachistoscope always had to hide hands and eight controlled information sent to each hemisphere.
- Standardised procedure- same images test individually to 1/10 of a second.
- Were all asked to be silent so that information is not passed between hemispheres and all had one eye covered --> standardised instructions.
Procedure - visual tasks
1)
Object were presented in the right or left visual field. He blind folded a participant and got them to look into one point in the middle of the screen, and then image was presented for 1/10 of a second and the person had to recall what they saw or had to pick up similar objects by touch from an array of objects.
If presented to the right visual field - the object went to the left hemisphere.
If presented to the left visual field - the object went to the right hemisphere.
Procedure- visual tasks
2)
Different visual stimuli were presented simultaneously to different visual fields (e.g. a dollar sign to the left and a ? to the right) and the participant was asked to draw with his left hand (out of sight) what he had seen.
- The dollar went to the right hemisphere.
- the ? went to the left hemisphere.
Procedure- visual tasks
3)
Two related words were presented simultaneously to the two visual fields (e.g. "key" to the left, and "case" to the right).
- the key went to right hemisphere.
- the case went to left hemisphere.
Procedure- visual tasks
4)
Simple arithmetic problems were presented to the left visual field (along with choice of answers)
- Information went to right hemisphere.
Procedure- visual tasks
5)
A nude pent-up was presented to the left visual field.
- Information went to right Hemisphere.
Procedure- tactile tasks
6)
Objects were felt by the left hand only (unseen by the participant).
- Information went to right Hemisphere.
Procedure- tactile tasks
7)
Objects were felt by the right hand only (and seen by the participants).
- Information went to left Hemisphere.
Results
1)
- If object were presented in the right visual field, the subjects were able to say what they had seen and could identify what it was from the array of pictures shown to the right eye by pointing to it and could find it with their right hand.
- If objects were presented in the left visual field the subject was unable to name it, but could draw it with the left-hand, they could identify it from an array of pictures shown to them to the left eye by pointing to it and could find it with their left hand from an array of objects.
Results
2)
When the word "case" is seen in the right visual field the participant can say the word case but can't draw it.
When the word "key "is seen in the left visual field it goes to the right hemisphere therefore the participant can draw it but can't say it and has no recollection of seeing it.
Results
3)
In the simple arithmetic problem the information went to the right hemisphere because it was presented to the left visual field. The right hemispheres were able to pick out and solve the simple mathematical problem.
Results
4)
When the new tenant was presented it went to the right hemisphere they would giggle and look embarrassed but couldn't say why they were laughing and looking embarrassed.
Results
5)
Objects felt by the left hand, went to the right hemisphere the participants could find it by touch in an array of objects using the left-hand but not there right.
Objects felt by the right hand, went to the left hemisphere, the participants could find it with their right hand and could name it but could not find the object with the left hand.
Conclusions
- Confirms that the left hemisphere is dominant for language.
- shows that the brain is made up of two independent hemispheres.
- Without the corpus callosum information is not passed between the two hemispheres.
Ethics upheld
Consent- the participants agreed to the names terms.
Debrief- they were debriefed.
Withdraw- they could withdraw.
Deception- they were all told the truth.
Confidentiality- the names weren't released.
Ethics broken
Harm- The study may have drawn attention to something that the participants might not be aware of in everyday life.
Key strengths
- Reliable-because of the controls for example, standardised equipment and instructions. No subject bias because the person could either see it or not.
- Ecological Validity- possibility that the tasks would be around in that situation is for example, rummaging in a handbag.
- Ethically valid.
Key weaknesses
- Ecological Validity- The findings would be unlikely to be reproduced in real life situation or to have any impact in real life because a person with a sethered corpus callosum who had both eyes open could be able to compensate --> information would not to be given for 1/10 of a second and wouldn't be in different fields of vision.
- Low validity- couldn't generalise because the participants had had major brain surgery, or had epilepsy and being taking medication for years.
There were individual differences in a small sample, larger differences would show clearly in a larger sample.
Improvements
1)
Problem: Sperry's sample was very small, only 11 participants as they are not many commissurotomy patients available to the study. This makes the findings difficult to generalise from a wider population in terms of lateralisation of function.
Improvements: you could change the design from independent measures to repeated measures, using 11 commisorotomy participants and a control group of 11 non-epileptic participants. You could test the participants before and after the operation asking them to perform the same task Sperry originally used.
Implications: not many people had had the operation and it could be hard to find people who haven't had the operation for epilepsy.
It would make the study more useful because it would show if the results were due to the commisorotomy.
If someone dropped out for the second test validity would be decreased. Demand characteristics could affect performance.
Impact: likely to show the same results because it is the same operation, but could be better because they have already done the tests before.
Improvements
2)
Problem: The sample maybe atypical as all the participants had severe epilepsy; the brain functioning may not have been "normal " as serious brain surgery or the fact that they been taking drugs for years may have caused unanticipated damage to the brain. This would mean that the findings would not be a valid reflection of functional terminalisation in "normal" participants.
Improvements: You could examine the functions within the brain using a PET scan which were not available at the time of Sperry's study. PET is going to look at the different levels of metabolic activity in the brain. You can identify the areas that work hardest when we are doing specific tasks e.g. solving mathematical problems. You could therefore study functional lateralisation without the need for commissurotomy patients. You could carry out tests similar to the tactile and visual tasks set by Sperry on a group of 30 patients, 15 males and 15 females and examine which areas of the brain are activated for the different tasks set.
Implications: Look at functional lateralisation but could show effects of commisorotomy.
Less able to control connection.
Better generalisability because it's bigger sample.
Objective measure-no biased results because it's a machine.
Expensive and time consuming but you could cross out epilepsy as a con founding variable.
Impact: highlight differences between males and female brains.
May find communication between hemispheres and may not find functional lateralisation.
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