Sperry (split brain study) Flashcards
Note (for Sperry):
What should you say instead of the brain?
What should you say instead of eyes?
Note:
brain = left or right hemisphere.
Eyes = left or right visual field.
Hand = hand.
If you’re right-handed, you’re left-hemisphere dominant.
Year that sperry was carried out?
1968
Why People have their hemispheres cut?,, sperry
The corpus callosum is sometimes cut by surgeons to reduce the effects of drug-resistant epilepsy. Epileptic seizures are caused by millions of brain cells firing excessively across the commissure and in simple terms overloading the electrically weaker side ( usually the non-dominant hemisphere)
When someone has a grand mal (a major epileptic episode) they have uncontrollable movements, seizures and eventually loss of consciousness (at serverest level can result in death.)
Theories for Sperry?
The right and left hemispheres are in many ways mirror images of each other. They deal with speech comprehension (Broca’s area and Wernicke’s area, respectively) showing their functions localisation (one specific thing). Functional lateralisation (brain works together) also exists because Broca’s and Wernicke’s area are only found in the left hemisphere.
The primary motor cortex is situated in the frontal lobe and areas in the right hemisphere receive information from and are concerned with the activities of the left side of the body and vice versa.
Sperry believes that studies involving split brain patients reveal the “true” nature of the 2 hemispheres because a commissurotomy which disconnects the 2 hemispheres means they can only work independently.
Backgrounds?, Sperry
Previous research using split-brain animals showing numerous behavioural effects (Mysers, 1961 and Sperry, 1967a and 1976b)
Other research by Sperry on both humans and monkeys who has undergone surgical section of the corpus callosum suggested the behavioural effect of this surgery may be less severe than other forms of cerebral surgery, eg.frontal lobotomy.
Research by Akelatisis (1944) also showed no important behavioural effects of surgical section of the corpus callosum humans, provided other brain damage was excluded.
More recent research by Spery et al using appropriate tests has actually shown a large number of behavioural effects that correlates directly with the loss of the neocortical commissures in humans as well as animals.
Aim? , Sperry
Using split-brain patients, was to show that each hemisphere:
- Possesses an independent stream of conscious awareness.
- Has its own separate chain of memories that are inaccessible to the other.
IVs? and DVs? Sperry
IV- having a split brain or not
DV- participants ability to perform a variety of visual and tactile tests.
What hemisphere controls what?, Sperry
Right visual field?
The left visual field?
Language?
Information from left hand?
Information from the right hand?
The right visual field: Left hemisphere
The left visual field: Right hemisphere
Language: Left hemisphere
Information from left hand: Right hemisphere
Information from the right hand: Left hemisphere
Research method?, Sperry
It is considered a quasi/natural experiment (IV wasn’t directly manipulated by the researchers.)
In a Laboratory environment.
No 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.
Very small sample, only 11 split-brain patients in this study (can be considered a collection of case studies.)
Materials/apparatus?, Sperry
Used a tachistoscope- this is a device that displays visual stimuli that are back projected onto a screen. Objects for tactile tasks such as keys.
The images are displayed very quickly, e.g 0.1 of a second.
Procedures?, Sperry
The participant has one eye covered and looks with the uncovered eye at a specific point on an upright back-projection screen (tachistoscope)
Visual stimuli tests:
Slides are projected onto the fixation point at a rate of 1 picture per 1/10 second. Participants then said or wrote what they had seen.
Tactile stimuli Tests:
Hidden objects are presented to the left or right hand (or both) behind the screen Participants must feel and identify or draw objects with the opposite hand.
Findings?, Sperry
Images and objects are only recognised when presented to the same eye or hand.
When an object is displayed on 1 half of the screen (i.e. the left) and then in the other the participants has no recollection of seeing it before.
Conclusion?, Sperry
The hemispheres are independent in terms of: perception, awareness and memory. (2 minds in 1 body)
The study can’t be generalised to a naturally occurring population because all participants suffered with epilepsy and received surgery.
Summary?, Sperry
The participants had the 2 halves of their brains disconnected (medical reason: Epilepsy) called a surgical commisectomy.
The apparatus allows visual images or objects placed exclusively onto the left visual field (which is processed only in the right hemisphere) or onto the right visual field (which is processed only in the left hemisphere)
There is no communication or sharing of information between the 2 hemispheres inside the brain.
So quite simply if you present an object into the right visual field the participants could say what it is (access to language centre on left side)
But if you present the same object to the left visual field, they could not day what it is (could not access language centre on left side)
The participants were right hand dominant, where the language centre is located in the left hemisphere, the right visual field sends information to the control left hand and vice versa and the right-side is superior for visual-motor coordination.
Methodological issues?, Research method and technique, Sperry
+ High internal validity. The use of objective tests to measure the patients capabilities provides an unbiased means of assessing the effects of the operation.
- Quasi experiment so certain confounding variables cannot be controlled.
