Vision and split brain Flashcards
How is vision processed in the brain?
- Vision from left of the nose is the left visual field
- This is picked up from both eyes
- This information crosses to the right hemisphere of the brain and is processed in the right visual cortex
- Vice verse for the right visual field
Why does separating the hemispheres control epilepsy?
Cutting the corpus callosum means seizures are contained in one hemisphere and cannot spread to the whole brain.
This is done when no other treatments work and is known as ‘hemispheric deconnection’ or ‘split brain’.
How did Sperry examine certain functions specialised in the two hemispheres?
- 11 patients had undergone a split brain operation as a treatment for epilepsy + a control group
- Natural experiment
- The procedure was designed to make it possible to get information into one hemisphere only, so that communication, perception and memory of each hemisphere could be tested
- A tachistoscope was used
- The patient focused on a dot in the middle of the screen
- Word/s flashed for 1/10 of a second so information only went to one hemisphere
- On table under screen and out of sight, items could be handled in the tactile tests
What would participants say of the word tree was projected to the right of the central dot?
Tree because the information in the right visual field goes to the left hemisphere and the area for speech production (Broca’s area) is in the left hemisphere.
If they use their right hand they can draw or find the object because the hand is contralaterally controlled by the same hemisphere. With the left hand, they cannot.
What was the tactile task participants did?
Participants simply had an object placed in their left or right hand and were then asked to find it from an assortment of objects without looking.
If participants used the same hand to find the object they could; if they used the opposite hand they could not.
OR they were asked to select the object which matched a word on the tachistoscope screen; again they could only find the object that the same field had seen.
What are the summary findings of split brain research?
When visual information is presented to the left visual field (and so right hemisphere) participants are not able to describe it and may say they saw nothing.
However, when information is presented to the right visual field (so left hemisphere) the participant can say what they saw.
This shows that language production is lateralised only to the left hemisphere.
The words flashing task shows that each hemisphere has a separate understanding and separate memory in a split brain patient.
Why is Sperry’s split-brain research useful?
Because it tells us that speech production is housed only in the left hemisphere - so we already knew this was primarily in the LH but not the extent of the specialisation.
It also tells us the importance of the corpus callosum + its role in whole brain communication.
What aspects of Sperry’s methodology made the research valid?
Participants stared at a central dot, information was flashed to one VF for 1/10 second so information only went into one hemisphere.
What aspects made Sperry’s methodology reliable?
Standardised equipment and tasks used for all participants. So it is replicable.
Relatively objective questions with clear right and wrong answers, which increase reliability.
What are the problems with Sperry’s sample?
Participants had differing degrees of surgery, differing levels of medication prior to the operation, and differing time periods since their operation.
These are problematic because the participant’s capabilities could have varied and affected the results. Ideally they would have screen + gathered very similar participants.
Sperry’s sample only had 11 participants in the ‘experimental’ condition. Why is this a problem?
Because it is unlikely to be representative of people with split brains therefore it may not be generalisable to all split-brain patients.
Sperry’s control group did not have epilepsy or the associated medication history. Why is this a problem?
Because these could have acted as confounding variables and affected the split brain patient’s capabilities; acting like another IV.
