Hemispheric Lateralisation and Split Brain Research Flashcards
Hemispheric lateralisation
Refers to the two different halves of our brain that control different functions. The left hemisphere is dominant for language and logic whereas the right is more involved in visual motor tasks as well as being used for creativity and holistic thinking. The two hemispheres are connected by corpus callosum which allows the left and right hemispheres to communicate to one and another.
Split brain research:
Sperry et al investigated hemispheric lateralisation by using split-brain patients. Split brain patients are people who had to go through a surgery due to epilepsy where the corpus callosum is cut.
Sperry Aims
Aims: They wanted to see the extent to which the two hemispheres were specialised for certain functions
Sperry Method
They present the patient with an image or a word on the left visual field, this gets processed by the right hemisphere as they are contralateral. This means if the right sees it, it goes into the left vise versa. But because they are split brain patients, and their corpus callosum is cut, it does not allow the information to communicate to the other hemisphere. If they were presented with a picture, they would be asked to describe what they see, in a drawing task they were told to draw what they saw.
Sperry Results
When they had to describe what they saw, if the information was seen through the right visual field, it would be processed by the left hemisphere which deals with logic and language, they were able to describe what they saw. But if the information was presented in their left visual field, which means that it would go to their right hemisphere, the patient could not describe what they saw and said there was nothing there because of the lack of language processing ability in the right hemisphere . During the drawing task, if they were presented the picture to their right visual field, which would be processed by the left hemisphere, they could draw the picture but it was not clear. When the picture was presented to the left hemisphere, leading to it being processed by the right, they could draw more clearly and better pictures, showing how it is superior when it comes to visual motor tasks.
Sperry Conclusion
They concluded saying left was dominant for speech and language, right was dominant for visual motor tasks.
- INCORRECT ASSUMPTION
Turk et al argues that language may not be restricted only to the left hemisphere. He discovered a patient who had suffered brain damage on the left hemisphere but they developed the capacity to speak in the right hemisphere, thus leading to them gaining the ability to speak about the information presented to both sides of the brain. This suggests that lateralisation is perhaps not fixed and the brain has the ability to adapt even after certain areas in the brain. This is a limitation because it highlights how the theory is incomplete and too narrow in its approach and requires more of a holistic way of viewing the brain. Modern neuroscientists have argued that there is a less obvious distinction between the two hemispheres as in a normal brain, the two hemispheres are constantly working together when doing different tasks. And much of the behaviour which is associated with one hemisphere can be performed by the other if the situation requires it. This therefore shows how there is plasticity in the brain where overtime, our brain adapts, and therefore supports Turk’s theory.
- IDIOGRAPHIC APPROACH
Another limitation of split brain research is that essentially, they are idiographic. This means that it was conducted on a small group as Sperry used only 11 patients. By using case studies, the results of the study remain subjective to the individual only as each experience is unique according to the person, and thus, it cannot be used to generalise to the whole target population and therefore is limited in its use. Reliability can therefore be questioned because of the small sample size and its reliance upon case studies. To overcome this, the researcher could have used a nomothetic approach where a larger sample of participants could be exploited through the use of meta analysis or they could have had a control group with people who had a history of epilepsy but did not have their corpus callosum cut. Nevertheless, one may argue that relying upon these subjective interpretations and using idiographic approach is better than using nomothetic approach because it allows psychologists to understand the cause and consequence of having split brain in depth, thus allowing them to find treatments and create therapies for support of suffering patients. For example, Sperry’s work did have practical value as it has allowed others to understand the roles of the different hemispheres.
+ SCIENTIFIC APPROACH
One strength of Sperry’s work is that his work was scientific. He had highly controlled the procedures, for instance, making sure that only one visual field was able to see the image by flashing it in a short amount of time (one-tenth of a second) which would not give them enough time to spread the information across both sides of the visual fields, and this was used for all the patients. Thus showing how he had used standardised procedures which increases internal validity. Because of this, it makes the information more accurate as it ensures that the manipulation of the IV, what tasks they did, resulted in the change in DV, what the outcome was and how well they performed. It ensured that no other extraneous variables impacted the result such as loud noise which would result in lack of focus. This therefore allows valid conclusions as well as cause and effects to be established, and also increases the credibility of psychology as a science as the results were objective and could be falsified by other psychologists.
