Sperry Flashcards
Aim
to show the independent streams of conscious awareness possessed by each hemisphere and to show how each hemisphere has its own memories.
Background
Previous research using split-brain animals showed numerous behavioural effects (Myers, 1961; Sperry, 1967a, 1976b).
Other research by Sperry on both humans and monkeys who had undergone surgical section of the corpus callosum suggested the behavioural effects of this surgery may be less severe than other forms of cerebral surgery eg frontal lobotomy.
Research by Akelaitis (1944) also showed no important behavioural effects of surgical section of the corpus callosum in humans, provided brain damage was excluded.
More recent research by Sperry et al using appropriate tests has actually shown a large number of behavioural effects that correlate direc the loss of the neocortical commissures in man as well as animals.
Sperry therefore set out in this study, using split-brain patients, to show that each hemisphere:
(1) Possesses an independent stream of conscious awareness.
(ii) Has its own separate chain of memories that are inaccessible to the other.
Method
This is usually considered a quasi/natural experiment because the independent variable (IV) - having a split brain or not - was not directly manipulated by the researchers. Participants with split-brains had already undergone hemisphere deconnection to reduce severe epilepsy. No actual control group was necessary for comparison in the study because the functions and abilities of the visual fields and hemispheres in non split-brain individuals was already known.
The dependent variable (DV) was the participant’s ability to perform a variety of visual and tactile tests.
It has, however, been argued that because such extensive tests were carried out on a very small sample (11 split-brain patients in total), this study can be considered a collection of case studies.
Sample
11 patients who had undergone ‘an extensive midline section of the cerebral commissures in an effort to control severe epileptic convulsions not controlled by medication’.
The first patient (a man) had his surgery over 5½ years before the study was conducted.
The second patient, a housewife and mother in her 30s had her surgery more than 4 years before the study was conducted. The other 9 patients had their surgery at varying times but not long before the study was conducted.
Procedure
Key tests
• Presenting visual information
The participant, with one eye covered, centred his gaze on a fixed point in the centre of an upright translucent screen. Visual stimuli on 35-millimetre transparencies were arranged in a standard projector and were then back-projected at of a second or less-too fast for eye movements to get the information into the wrong visual field. Everything projected to the left of the central meridian of the screen is passed via the left visual field (LVF) to the right hemisphere and vice versa (regardless of which eye is used).
Presenting tactile information
Below the translucent screen there was a gap so that participants could reach objects but not see their hands. Objects were then placed in either the participant’s right / left hand or both hands. Information about objects placed in the left hand is processed by the right hemisphere and vice versa.
Participants undertook a variety of both visual and tactile tests.
This apparatus is called a tachistoscope.
Results
Visual tests
Information shown and responded to in one visual field could only be recognised again if shown to the same visual field.
Information presented to the RVF (LH system of a typical right-handed patient) could be described in speech and writing (with the right hand). If the same information is presented to the LVF (RH), the participant insisted he either did not see anything or that there was only a flash of light on the left side ie the information could not be described in speech or writing. However the participant could point with his left hand (RH) to a matching picture/object presented among a collection of pictures/objects.
If different figures were presented simultaneously to different visual fields eg $ sign to the LVF and ? to the RVF, the participant could draw the S sign with his left hand but reported that he had seen a?
Tactile tests
Objects placed in the right hand (LH) could be described in speech or writing (with the right hand). If the same objects were placed in the left hand (RH) participants could only make wild guesses and often seemed unaware they were holding anything.
• Objects felt by one hand were only recognised again by the same hand eg objects first sensed by the right hand could not be retrieved by the left.
When two objects were placed simultaneously in each hand and then hidden in a pile of objects, both hands selected their own object and ignored the other hand’s object.
Conclusions
People with split brains have two separate visual inner worlds, each with its own train of visual images.•
Split-brain patients have a lack of cross-integration where the second hemisphere does not know what the first hemisphere has been doing
+Split-brain patients seem to have two independent streams of consciousness, each with its own memories, perceptions and impulses ie two minds in one body
Data - qualitative
S- Point….Qualitative data was collected which increases internal validity of the results.
Explain – This type of data provides an in-depth description therefore painting a fuller picture of the situation and ensuring the researcher is measuring what they set out to.
Explain/evidence….This is useful for Sperry to gain an in-depth understanding of how split brain patients respond to material presented to the left and right hemisphere e.g. when a nude picture was presented to the right hemisphere the participants would laugh but state they had not seen anything.
W - Point….Qualitative data was collected which is open to subjective analysis.
Explain – This means the researcher may interpret the findings to enable them to provide their own predictions and therefore lowering the validity of the results.
Explain/evidence…. Sperry may have only included accounts of the participants having an emotional reaction to the nude picture, when presented to the right hemisphere (RH), and ignored participants who failed to react or other rational for reactions. He may have done this as he believed prior to the study that emotion was held in the RH.
Data - quantitative
S - Point….Quantitative data was collected which is objective in its analysis.
Explain – This means the personal opinions and predictions of the researcher should not interfere with the analysis and therefore this increases both the internal validity and reliability of the results.
Explain/evidence….In the Sperry study participants could either do the task being asked of them (e.g. verbalise something they had seen in one of their visual fields) or not. Another researcher should interpret this data the same way.
W - Point….Quantitative data is low in internal validity.
Explain – Statistics can merely point out patterns or differences but does not provide explanations regarding why the results were found and therefore we cannot confidently say they were caused by the IV.
Explain/evidence….In the Sperry study we learn that patients could not describe the images displayed to their left visual field, however there is no qualitative data gathered from participants to explain why this was the case.
Methpd evaluation
S - Point….A quasi experiment has increased ECOLOICAL VALIDITY
Explain…As the I.V. is not manipulated the P’s fall naturally into their condition so should display more natural behaviour.
Evidence…Split brain patients had already had a Commissurotomy so their left and right hemisphere no longer communicated so they will show natural reactions to the tasks carried out.
W - Point…In quasi experiments participants naturally fall into the conditions and therefore individual differences can be an issue.
Explain…This means participants may possess characteristics in one condition that could affect the measure of the DV and lower its validity, it may not be measuring the impact of the IV.
Evidence. In the study by Sperry all the brain-split patients had suffered from severe epilepsy and therefore the seizures that they had experiences may have altered how their brain (hemispheres) functions. Therefore, the study may measure the impact of the epilepsy rather than the surgery.
Ethics
Point…The study may break the ethical guideline of protection from harm.
Explain..P’s may have felt distressed by the procedure.
Evidence…Split brain p’s may have felt distressed by not being able to verbally described items during the visual tasks
Reliability
Point…The study is high in internal reliability
Explain..a standardised procedure was used to ensure that the study could be repeated and the consistency of the results checked.
Evidence…All p’s carried out the same visual and tactile tasks, such as when a picture of a nude was flashed to the right hemisphere. This ensured all P’s were tested in the same way.
Validity
Point….The study has high internal validity
Explain…controls are put into place to ensure a accurate measurement is taken
Evidence…Sperry flashed images up for one tenth of a second to ensure that the information is only processed in one hemisphere in order to test the function of each hemisphere separately.
