- Sperry studied the abilities of split-brain patients.
a) Describe one difference between the ability of split-brain patients and ‘normal’ people to identify objects by touch alone. (2)
b) Give one explanation for this difference. (2)
- Normal people are able to identify objects by touch alone regardless of which hand they have touched the object with. However split-brain patients are only able to identify an object if it has been placed in the right hand (LH) by naming it in speech and writing. If an object is placed in the left hand (RH) split-brain patients can only make wild guesses and may seem unaware that they are holding anything.
- This is because the two hemispheres of the brain in the split-brain patients are disconnected because their corpus callasum has been severed and information cannot pass from one hemisphere to the other.
- a) From the study by Sperry, explain why the split-brain operation was carried out on the patients of this study. (2)
B) Outline the major function of the corpus callosum. (2)
- The split-brain operation was carried out on the patients because it is a possible remedy of epilepsy. it involves cutting through the cerebral commissures which separate the two hemispheres thus preventing the spread of an epileptic attack from one hemisphere to the other.
- The corpus callasum is a bundle of nerve fibres that connect the two hemispheres; the major function is allowing information to be passed between them.
- The results of Sperry’s study of split-brain patients suggest that we effectively have two minds. Outline two pieces of evidence from the study that show this. (4)
1) If a $ sign is flashed to the left visual field and ? sign is flashed to the right visual field the P can draw the $ figure with his left hand (perceived by right hemisphere) but will tell you that he saw the ? sign which was shown to the RVF ( left hemisphere)
2) When words are flashed partly to the LVF and partly to the right visual field, the letters are responded to separately. For example ‘keycase’ is projected (key to LVF and case to RVF) then a P would :
- select a key from the collection of objects with his left hand (LVF goes to right hemisphere which controls the left hand)
- spell out the word ‘case’ with his right hand (RVF goes to left hemisphere which controls the right hand)
- say case if asked what word was displayed (RVF goes to the left hemisphere which controls speech)
3) Objects placed in the right hand can be (left hemisphere) can be named in speech and writing
4) If an object is placed in the left hand Ps can only make wild guesses and may seem unaware that they are holding anything.
- a) Describe the technique Sperry used to present information to only one side of the brain. (2)
B) Explain why ‘normal’ people do not have any difficulty with the technique used to test the split-brain patients. (2)
- The P has one eye covered and is asked to gaze at a fixed point in the centre of a projection screen. Visual stimuli are back-projected onto the screen, either to the right or left of the screen, at a very high speed – one picture every 0.1 second or less.
- Normal people do not have any difficulty with the technique because their corpus callasum is not severed and visual stimuli presented to one hemisphere can be shared with the other hemisphere via the corpus callosum.
- From the paper by Sperry on split-brain patients, outline evidence which indicates that language is processed in the left hemisphere of the brain. (4)
- Objects placed in the right hand (left hemisphere) can be named in speech and writing.
- When words are flashed partly to the LVF and partly to the RVF, the letters are responded to separately. For example if the word ‘keycase’ is projected (key to the LVF and case to the RVF) then a P would 1) spell out the word ‘case’ with his right hand (RVF goes to the left hemisphere which controls the right hand) and 2) say ‘case’ if asked what word was displayed (RVF goes to left hemisphere which controls speech)
- If the ? sign was flashed to RVF the P will tell you that he saw the ? sign which was shown to the RVF (left hemisphere).
- a) In Sperry’s study, describe one problem with generalising from the sample. (2)
B) Explain what is meant by the term ‘left visual field’ as used in the paper by Sperry. (2)
- Sperry did not control the IV, he was not able to test these Ps prior to the operation, possible that their brain functioning may have been atypical (different from the norm) before the operation and this would make it difficult to draw conclusions about the functions of the hemispheres in non-separated brains.
- The left side of the body and the left visual field are controlled by the right hemisphere. Information presented to the left eye i.e. left visual field will be perceived by the right hemisphere.
