Hemispheric disconnection and unity in conscious awareness – Sperry 1968. Evaluation In 1968 the neuropsychologist conducted a study into split brain patients while working at the California Institute of Technology. Previously he had carried out research similar to this, in the1950s, splitting the brains of cats and monkeys. It was during this research that he realise3d that you could teach one of the hemispheres a task, while keeping the other hemisphere unaware of the information learned. This discovery supported the idea that the brain consisted of two independent pieces as opposed to one unified brain.
The importance of this work was appreciated when he won a Nobel Prize in 1981. This study was performed to further this research that he had carried out, this time, on humans. The brain splitting operation was not simply done for the study, as this would have been unethical, participants had had their brains split un an attempt to stop epileptic fits in epileptics. The operation used on the epileptics was called a commisurotomy, where all the bundles of nerves connecting the two halves (hemispheres) of the brain are cut, even the less major ones.
Sperry’s aim with this study was to investigate the effects of isolating the two hemispheres from each other, and to show that the hemispheres have different functions. Sperry wanted to map lateralisation of the brain and show that information in one side of the brain is not available to the other side. This study comes under the Physiological approach (or the Bio-Psychological approach). This approach uses biology and psychology to explain various behaviours. It involves studying the nerves and chemicals in the body, especially the brain.
The physiological approach’s development is closely linked to the development of new technologies for observing and measuring the body. Although it isn’t really a school of psychology as such, it has a strong tendency towards the reductionist approach, ‘Reducing’ behaviour to its neuronal and biochemical elements. Looking at behaviour at its ‘root’. The design of the study was a quasi – experimental design which compared split brain subjects with the normal subjects, and compared case studies of all the individual patient participants. This is a laboratory experiment.
One advantage of this quasi – experimental design is that there is less chance for the experimenter to interfere with the variables, considering that the independent variable is ‘naturally occurring’ so to speak. This lack of interference increases the reliability of the results obtained, and also the validity of the study. An advantage of the Bio-Psychological approach is that there is very little room for interpretation of the results as you are studying behaviours at their core, as opposed to having to infer the reason for the behaviour.
A disadvantage of the methodology of this study is that it is a lab experiment, meaning that it lacks in ecological validity, as many of the tests carried out on the participants would not occur in real life. A further disadvantage of this design is that it allows for demand characteristics, in that the participants may realise the aims and purposes of the study and thus intentionally produce desirable results, or perhaps undesirable results. The participants in this study where a group of patients who suffered from severe epilepsy, which couldn’t be controlled by medication.
The participants had undergone a commisurotomy, a possible remedy to epilepsy. The sample was a self-selecting sample, due to the rarity of people who had undergone the commisurotomy. Two of the participants had undergone the surgery some time before the study; the other 9 had only recently A representation of the apparatus used. A representation of the apparatus used. undergone the operation. The Procedure This study used equipment that allowed the participants to have various sensory stimuli presented to either hemisphere of the brain in various combinations.
Visual stimuli were presented via a projector projecting images onto a screen, tactile (touch) stimuli were presented to either the left or right hand, or both, without the participant being able to see what the objects were. Subjects were asked to remain silent during the study, except when asked to answer questions verbally by the experimenter. This was to prevent them from passing information from the left side of the brain to the right side, as sound can be taken in by both ears and thus both hemispheres simultaneously.
The participant could say what object they see or feel, thus making the information available to both hemispheres. The study took place in a laboratory, under controlled conditions. Each of the participants were tested using exactly the same procedure in the same conditions as each other. The independent variable in this study was whether the participant had had the commisurotomy operation, and had had their corpus callosum severed while the dependant variable was how they performed in the various tasks that they were presented with. The procedure is split into four different sections: Visual Investigations * Tactile Investigations
* Visual and Tactile information * Tests of the Right Hemisphere. “The method used was a natural (also called quasi) experiment. The quasi-experiments involved comparing the performance of the 11 participants on various tasks with the performance of people with no inter-hemisphere disconnection. The independent variable was therefore the whether a person had hemisphere disconnection or not and the dependent variable was the participants performance on the tasks. ” ~ http://www. holah. karoo. net/ The method used was a natural (also called quasi) experiment. The quasi-experiments involved comparing the performance of the 11 participants on various tasks with the performance of people with no inter-hemisphere disconnection. The independent variable was therefore the whether a person had hemisphere disconnection or not and the dependent variable was the participants performance on the tasks. ” ~ http://www. holah. karoo. net/ Visual investigations These involved showing one stimulous to one visual field or showing two different stimuli to the two different fields.
When targeting one visual field the participant would have one of their eyes covered and told to look at a point in the centre of the screen. An image was then projected to either the left or right side of this point for a tenth of a second, long enough for the participant to see it, but not long enough for the participant to move their eye and have the object enter the wrong side of the visual field. When targeting both visual fields, the participant would again look at the point in the centre of the screen, while two images were rojected, again for 1/10th of a second. One image to the left of the point and one to the right. The participant would then be asked to say what they had seen, the typical response from someone who had undergone the commisurotomy would be a key, and would have no conscious awareness of seeing anything else. They would then be given a pen in their left hand (out of their line of sight) and would be asked to draw what they had seen, and they would typically draw an apple, but have no knowledge as to why they had drawn this.
Tactile investigations When experimenting on just one hand, the participant’s hands would be hidden from their view, behind a screen, they would then be asked to select the item they had just seen, from an assortment of items. Only one hemisphere would have been shown the item. Another experiment involved placing an object in one of their hands without them seeing their hands, and asking them to say what they are holding.
A variant of this involved them having to point to what they had been given instead While experimenting with both hands at the same time, both hands are out of sight, one object is placed in each hand then taken away. The subject is then asked to either find the item by touch from a pile of items or to say what the item was. Another test including both hands consisted of holding both hands out, out of sight, without the hands touching. The experimenter would then place one hand in a certain position, the subject would then be asked to copy this position with the other hand.
A final method of testing using both hands is similar to the previous method, but the experimenter only touches a point on the hand, and the participant is asked to touch the same place on the other hand, with that hand’s thumb. Visual and tactile investigations The participant was presented with an image of a hand with a black spot marked, to either the left or right visual field. The subject was then asked to touch the same point with the tip of the thumb of the same hand. Tests of the right hemisphere
As the right hemisphere doesn’t produce language, Sperry decided to cary out tests to check for its ability to work logically and experience separate emotions from the left hemisphere. He did this in three ways: The left visual field is presented with an object and the subject is asked to pick out similar objects by touch. Basic maths problems are presented to the left visual field, and the participant is asked to solve them using the left hand. The subject is asked to rank objects by size shape or texture using their left hand.
The controls in this study were that all participants experienced exactly the same tests. The study produced both quantitative results and quantitative results, due to the fact that it was part quasi experiment, part case study. The results * If a projected picure is shown and responded to in one visual field, it is only recognised again if it appears in that visual field. * If visual material appeared in the right visual field (processed by left hemisphere), the patient could describe it in speech and writing as normal. If the same visual material is projected to the left visual field (right hemisphere) then the participant says he did not see anything or there was just a flash of light on his left side (language in the left hemisphere) * If you then ask the same participant to use his left hand (right hemisphere in control) to point to a matching picture or object in a collection of pictures / objects, then he points to the item he insisted he couldn’t see. These results show that the right hemisphere cannot speak or write (aphasia and agraphia)