Split-brain research into hemispheric lateralisation

Question 1

Define hemispheric lateralisation

Answer 1

Looks at behaviours controlled by just one hemisphere
EG: language is usually controlled by the left hemisphere

Question 2

Describe a split brain study

Answer 2

Sperry (1968) wanted to demonstrate that the two hemispheres were specialised for certain functions and could perform tasks independently of one another
Sperry studied a group of epileptics who has their corpus callosum (connection between the left and right hemispheres) cut

Question 3

What was the procedure of Sperry’s split brain study?

Answer 3

An image or word is projected to a patient’s right visual field RVF (processed by the left hemisphere) and another image to the left visual field LVF (processed by the right hemisphere)
In a normal brain, the corpus callosum ‘shares’ information between both hemispheres but this can’t happen in these participants

Question 4

How did the patients describe what was seen in Sperry’s study?

Answer 4

Objects shown to:
RVF - patients easily describes what is seen
LVF - patients say there’s nothing there
They can’t describe objects in the LVF because the right hemisphere usually lacks language centres
Messages recieved by the right hemisphere are normally relayed via the corpus callosum to language centres in the left hemisphere

Question 5

Describe recognition by touch in Sperry’s experiment?

Answer 5

Objects shown to the left visual field:
Could not name them but could select a matching object using left hand (connected to the right hemisphere recieving information from the left visual field)
Left hand could also select an object that was associated with image presented to the left visual field (eg: ashtray selected in response to a picture of a cigarette)
In each case, the person could not verbally identify what they had seen (left hemisphere needed for this) but could understand what the object was (right hemisphere) and select the object

Question 6

What happens with composite words?

Answer 6

Two words presented either side of the visual field - key on the left, ring on the right
Selects key with left hand (LVF goes to RH to left hand)
Says the word ring (RVF linked to LH with speech centres)

Question 7

Give a strength of split-brain research

Answer 7

Methodology - Sperrys made sure that his research was standardised and his presenting of the visual information to one hemispheric field was ingenious
This allowed Sperry to vary aspects of the basic procedure and ensure only one hemisphere recieved information giving useful and well-controlled results

Question 8

Give 3 limitations of split-brain research

Answer 8

1. Counter point to methodology - However, some believed that Sperry’s experiment lacked controls: extent of disconnection between hemispheres varied, lack of valid control groups, may be additional effects of surgery other than just procedure, some patients had experienced drug therapy for much longer than others
2. Research is too general - Researchers have said that these findings cannot be widely accepted, as split-brain patients are such an unusual sample of people
   Only 11 patients took part and all had a history of seizures. This may have caused unique changes in the brain that influenced the findings
   This limits the extent to which the findings can be generalised to normal brains, reducing the validity of the conclusion
3. Hemispheric functions may be overstated - Sperry’s work is a growing body of “pop-psychological literature” that oversimplifies and overstates the difference in function between the two hemispheres
   Modern neuroscientists argue these distinctions are not all clear-cut
   Many behaviours that are associated with one hemisphere can be performed by the other when situations required
   Therefore, is Sperry’s research too simplistic?