Sperry - Split Brain Flashcards
What is epilepsy?
- Neurological disorder
- Sensory disturbance and loss of consciousness
- Abnormal electrical activity in the brain
Method
Quasi experiment.
Quasi (natural) as IV out of the researchers control. The participants already had epilepsy and needed a commissurotomy.
What is a commisurotomy?
Operation needed to control severe epilepsy
What is the IV?
Split brain/intact brain.
What is the DV?
Performance on tasks.
What is the research design?
Case study.
Sample size
11 total.
2 participants had been operated on successfully some time before experiment.
9 recently undergone surgery.
What type of sample was this study?
Opportunity sample
Why did these participants have the commisurotomy?
Their epilepsy could not be controlled by drugs.
They had the operation to help, therefore they could then be used to study the effects of hemispheric deconnection on behaviour.
3 research questions.
- What happens when the two halves of the brain are disconnected?
- Do the hemispheres perform different functions?
- Does each hemisphere have its own memories, perceptions and concepts?
Brain structure background
- Two hemispheres in the brain.
- Brain is bilaterally symmetrical. (mirror images of each other)
- connected by nerve fibres = corpus callosum.
- corpus callosum enables hemispheres to share information.
What does the Left Hemisphere control?
- Right hand side of the body
- Right visual field goes to left hemisphere
- Controls Speech (words and ability to do so) and Writing
- Language skills
- Allows us to reason things out.
What does Right Hempishere control?
- Left hand side of the body
- Left visual field goes to right hemisphere
- Controls creativity and emotional responses
- ‘Pictures’ hemisphere and specialises in tasks such as drawing, spatial awareness and intuitive tasks
What are the 5 controls in this study?
1: All visual and tactile materials are presented using the same testing set = tachistoscope
2: All participants had one eye covered throughout visual tests
3: All visual material presented to either LVF or RVF for 0.1 second or less
4: All tactile tests the participants could not see their hands
5: All participants undergone a commissurotomy to contain severe epileptic convulsions.
What were the conclusions from this study?
When the brain is disconnected we see two separate selves, each with its own memory and will.
- the right hemisphere controls emotional responses
- language skills are based in the left hemisphere
- left hemisphere = words and ability to speak. Also allows us to reason things out
- right hemisphere = ‘pictures’ hemisphere and specialises in tasks such as drawing, spatial awareness and intuitive tasks
- information received by one hemisphere is not accessible to the other hemisphere in spilt-brain patients
- the individual has separate streams of consciousness with a severed corpus callosum.
- -
What is the procedure of this study?
- One eye covered
- Gaze at fixed point in centre of projector screen
- Picture displayed every 0.1second or less
- Displayed to LVF or RVF, therefore the eye only had time to process the image in the VF it was placed
- Below the screen there was a gap so that he participants could reach objects but not see his or her hands
- Unless asked questions by the experimenter the subjects had to remain in silence throughout the experiment, therefore could not pass information from Left to Right Hemisphere as sound can be taken in by both ears simultaneously.
Aim
To investigate the hemispheric functioning of split brain patients
Procedure of the visual investigations.
- Flash one stimuli at a time to one VF or two stimuli simultaneously to two different fields
- Identify what they saw through speech, writing or drawing
Procedure of tactile investigations
- Place an object in one hand or the other, or both hands simultaneously
- Participant unable to see what they are holding
- Asked to identify what they had been holding through speech, writing, drawing or manual selection from various objects.
What is it vital to do when using results?
!! MAKE REFERENCE TO BOTH VISUAL AND TACTILE RESULTS !!
Results for visual stimuli to one visual field.
- Image shown and responded to in one VF then only recognised if presented to the same VF
- RVF: point to matching picture or object in collection of pics/object with his right hand
- LVF: ~ Said he did not see anything or that there was a flash of light on his left side/was unable to name it.
~ Could draw it with eyes closed with left hand.
~ Point to matching picture or object with left hand from a collection of pics/objects - even though he had just insisted he had not seen anything.
Results from visual stimuli to both visual fields.
LVF . RVF
$ . ?
LVF . RVF
Key . Case
- Draw $ with left hand, however verbally identify ?
- When words flashed, letters responded to separately:
~ select a key from a collection of unseen objects with left hand
~ write the word ‘case’ with right hand
~ say the word ‘case’ if asked what word had been presented
Results from tactile investigations.
- Object placed in right hand = named in speech and written with right hand
- Object placed in left hand = participants made wild guesses as to what they were holding no some seemed unaware they were holding anything. However participants could find the item on a bag with other objects with left hand
- Unable to retrieve an object with right hand if sensed first with left hand
- Two objects placed simultaneously in each hand and then hidden in a pile of objects, both were able to select own object from the pile but ignored the other hands object.
Name 3 changes that could be made to this study
1: Larger sample size to 50
2: Use 50 epileptic subjects who had not had their hemispheres deconnected as a control group
3: Change procedure eg. By using auditory testing
Why do these patients not experience these problems in everyday life?
- Normally an individual does not have only 0.1 second to identify material flashed to one visual field only, they have time to compensate moving their eyes so the material is received in both visual fields and therefore allows them to correctly identify the material
- Frequently speech and sound in involved which allows the patients major hemisphere (left) to talk to the minor hemisphere (right) do material is identified through auditory channels.
- The inability shown by patients to identify objects presented first to one hand and then the other is usually not a problem because the presentation is normally accompanied by visual cues which allow the patient to recognise the object
What evidence is there to show that one hemisphere does not know what the other hemisphere has been doing?
- If an object was placed in the left hand participants could not identify it, but could select it from other objects in a grab bag with same hand
- An object was placed in the participants right hand could be identified or named in speech or writing, where as if the same object was placed in the left hand the participant could only make wild guesses or seemed unaware they were holding anything
- If two different figures were flashed simultaneously to the right and left visual fields and the participant were asked to draw what he saw using his left hand out of sight, he regularly produced he figure he had seen in the LVF. However when asked what he had drawn he would say whatever had been presented to the RVF
Why had they previously undergone an operation to reconnect two hemispheres?
Participants previously suffered rom severe epilepsy which could not otherwise be controlled by medication.
To reduce effects of epilepsy.
Problems with generalising sample
Sample too small (11) so can’t generalise to wider population.
All participants had the spilt at ion to cure epilepsy and epilepsy may alter the brain, therefore cannot generalise to non-epileptics
