Method and design of the study
The study involved patients who all had underwent the corpus callosum being severs in order to alleviate their epilepsy. The experiment contained various tasks, such as the investigation of how visual, tactual or auditory stimuli were affected in patients with a split-brain condition.
In one of the tasks, a visual stimulus was presented to the patient. The patient, who is sitting down, is looking straight ahead, focusing on a black dot in the middle of the screen. A single word or an image was then presented on the screen on either the right or the left hand side for less than one second. The reason being to ascertain that no eye movement was made by the patient, in order to prevent information being received by both visual fields. Whenever a stimulus were presented to the right visual field, the patients were unable to define what they had seen.
In a second task, two visual images were presented simultaneously, one on either side of the visual field, for instance a shovel presented to their left visual field and a chicken to their right. The patient was then asked to draw what they had just seen with their left hand, the patient had no problem identifying the object seen through their left visual field, drawing a shovel. When asked what they had drawn, they would answer what they had seen from their right visual field, which was a chicken. Due to the information not longer being able to transmit between the two hemispheres the patients were unable to process the visual information they had received.
For the study to be successful it was designed in a way to ensure that a certain stimulus would only pass through either the right or the left visual field at the time. By focusing on a dot presented at the middle of the screen, this was made possible.
Result and further explanation
Due to the splitting of nerve fibers in the corpus callosum the seizure impulses have a greater difficulty transmitting information between the right and the left hemisphere. The outcomes of this procedure are, among other things, short-term memory deficits, difficulties in speech and processing information.
Sperry argued that one human being is of two minds, each working separately when information is received, stating that there is a so called lateralization of function. For instance, in a normal human brain, when information is received through a stimulus, entering either the left or the right hemisphere, it is quickly transferred to the other in order to fully process the information received. However, the two hemispheres in a split-brain patient are unable to communicate resulting in the two hemispheres working as two separate minds. It can be explained that when the patients were presented with an image in their left visual field, they were unable to vocally convey what they had just seen. This is due since the visual stimuli were only sent to the right hemisphere, and because speech is dominated by the left hemisphere, the patients were unable to express what they had seen. Though, when asked if they could draw or point out what object they had seen, it was successfully done without any difficulties. It can simply be put as the right hemisphere would match the object by appearance, while the left hemisphere would match by the function of the object.
Major contributions made from this study includes how each cerebral hemisphere specializes in different tasks; the left hemisphere concentrating on more analytical, logical, and verbal tasks, whereas, the right hemisphere dominating in spatial abilities and visual imagery. During this era it was also discovered how each hemisphere had the ability to control different parts of the body. The left hemisphere controlling the right side of the body, whereas the right hemisphere controls the left side. Through studies like this, it has given scientists and psychologists a greater knowledge in understanding how the cerebral hemispheres functions, as well as the human brain in general. It has also given a vast improvement on how to treat various neurological illnesses including epilepsy, Alzheimer’s and stroke.
