Sperry Flashcards
Background
Epilepsy is a condition is brought on by abnormal electrical impulses discharging within the brain disrupting normal brain patterns.
In the 1940’s a treatment was developed called ‘Split Brain Surgery’ (called commissurotomy) that included the corpus callosum being cut so that the abnormal electrical impulses could not spread throughout the brain.
Sperry thought that patients who had undergone split brain surgery were perfect participants for research into what each hemisphere of the brain actually does
Key Terms
Lateralisation of Function
One side/hemisphere of the brain has a different role from the other
Key Terms
Corpus Callosum
Fibres that carry the majority of information between the two hemispheres of the brain
Key Terms
Contralateral Control
The idea that each side of your body is controlled by the other side of your brain
Key Terms
Commisurotomy
Surgical operation to sever the corpus callosum (a.k.a ‘Split Brian Surgery’)
Aim
To study the functions of separated and independent hemispheres
Sample
- 11 patients who had undergone a commisurotomy as a treatment for their epilepsy. They were obtained from a surgery in America
- They were compared with a group of people who had not undergone the surgery and were not epileptic
Visual Fields
- Each eye has two visual fields
- Right visual field is linked to left hemisphere
- Left visual field is linked to right hemisphere
Equipment
- Sperry used a tachistoscope to show participants images that lasted for 0.1 seconds (one eye was covered)
- The screen allowed an image to be shown to just one visual field, or different images to be shown to different visual fields
- The screen had a dot in the middle (called the fixation point) for participants to focus on
- The screen hid the participants’ hands from view, so they could hold and feel objects without seeing them
Controls
- Symbols displayed
- Images displayed
- Objects used
- Fixation point
- 0.1 seconds time displayed
- Hands out of view
- One eye covered
- Tachistoscope
Procedure & Findings
Image shown to RVF
Info goes to LH and they could say what they had seen
Procedure & Findings
Image shown to LVF
Info goes to RH and they could draw/point to the object with their left hand but could not say what they had seen
Procedure & Findings
Apple shown to the LVF and key to the RVF
Key goes to LH, apple goes to RH. They would say they had seen a key but their left hand drew an apple
Procedure & Findings
Simple maths problem shown to the LVF
Info goes to RH and they could point to the answer with their left hand
Procedure & Findings
Nude image shown to LVF
Info goes to RH and they giggle/look embarrassed but cannot say why
Procedure & Findings
Object held with right hand
Info goes to LH and they could name what they felt or write it
Procedure & Findings
Object felt with left hand
Info goes to RH and they could point to or find again the object with their left hand but they couldn’t say what they had felt
Conclusions
- Left Hemisphere - Has written and verbal language ability and control the right side of the body
- Right Hemisphere - Can only communicate non-verbally and controls the left side of the body
Evaluation
Ethics
- Informed Consent - Participants consented to participate following being approached through their hospital
- Confidentiality - Details of each particpant were kept confidential
- Protection from Harm - May have been upsetting or embarrassing to not have full capabilities or understanding of your behaviour
- Deception - Participants were fully aware of the research
Evaluation
Ethnocentrism
The sample were obtained from a hospital in America (so highly ethnocentric) but the roles of each hemisphere should be universal to all humans so perhaps it doesn’t matter
Evaluation
Reliability
- Internal Reliability - Procedure was very standardised so high (though 2 participants had the surgery 4-5 years ago so may have recovered)
- External Reliability - Sample perhaps not large enough to establish consistent effect
Evaluation
Validity
- Internal - Perhaps the behaviour can be explained as a result of epilepsy, not the surgery (low construct validity)
- External (population) - The sample was very specific so perhaps not generalisable
- External (ecological) - The visual procedure was not very realistic as we see things for longer than 0.1 seconds so our brains could adapt. The tactile procedure was more realistic as feeling around and not being able to see your hands is relatively normal
