Lateralisation of function

How is the brain divided?

into the left and right hemispheres

What is hemispheric lateralisation?

specialised areas associated with language are found in one of the hemispheres rather than both

Who performed split-brain research?

Roger Sperry

What were the characteristics of participants who took part in Sperry’s split-brain research? (2)

they had all had a history of severe epileptic seizures, had all undergone a commissurotomy

What were characteristics of participants in the control group of Sperry’s split-brain research?

individuals who had no history of epilepsy

What is a commisurotomy? (2)

the severance of the corpus callosum, removing the main link of communication between the two hemispheres

Why did Sperry choose the participants who had a commisurotomy? (2)

it allowed Sperry to see if the two hemispheres were specialised to certain functions, and if the hemispheres perform tasks independently

What is the corpus callosum? (2)

A bundle of nerve fibres that joins the two hemispheres, responsible for communication between the two hemispheres

What was the aim of Sperry’s split-brain research? (2)

Sperry used visual and tactile tasks to test hemispheric lateralisation, using a T-scope

Why did Sperry use a T-scope? (2)

allows each hemisphere to be tested individually, by participants focussing on a fixation point

What was Sperry’s hypothesis about split-brain research? (2)

split-brain patients will not be able to verbally describe an image or word that is presented to their left visual field, while controls will have no difficulty

Why did Sperry make this hypothesis? (2)

the information presented to their left visual field is processed by the right hemisphere that does not contain a language centre, the two hemispheres of the brain cannot communicate with each other in the commisurotomy patients

What was step 1 of Sperry’s method? (2)

participant asked to focus on the fixation point, an image or word is projected for 1/10th of a second to one or both visual fields

What was step 2 of Sperry’s method to test for non-verbal processing? (2)

participants were asked to pick up or match objects that were out of sight

What was step 3 of Sperry’s method? (3)

participants were asked to describe the object, image or word that had been presented to them, and sometimes asked to draw what they had seen or touched

How and why would findings be expected to differ between commisurotomy participants and the control group? (2)

in the control group’s brains the corpus callosum would share information between both hemispheres giving a complete visual picture, but presenting the image to one hemisphere of a split-brain patient meant that information could not be conveyed from one hemisphere to the other

What were the results when a picture or word was projected to the right visual field, processed by the left hemisphere, in the commisurotomy patients? (3)

the patient could easily describe what had been shown, supporting hemispheric lateralisation, showing how language is processed in the left hemisphere

What were the results when a picture or word was projected to the left visual field, processed by the right hemisphere, in the commisurotomy patients? (3)

the patient could not describe what had been shown and often said there was nothing there

Although commisurotomy participants could not desire what was shown in their left visual field, what could they do? (4)

they could use their left hand to point to the matching object or picture, showing how the right hemisphere processed the information, right hemisphere controls the left hand, but they cannot verbalise it

What were the results from commisurotomy patients when two words or pictures were projected at the same time on each visual field, for example a dollar sign on the left, a question mark on the right? (2)

commisurotomy patients would say that they saw a question mark, but when they were asked to draw what they saw with their left hand they drew a dollar sign

What is important to note about the results of the commisurotomy patients being presented pictures to both visual fields?

the patients were not aware they had drawn a different object or picture to the one they had seen

What does this suggest? (2)

suggests that the two hemispheres were working separately from each other, drawing ability is dominant in the right hemisphere

What were the results when an object was placed in the commisurotomy patient’s right hand?

the object could easily be described or named in speech or writing

What were the results when an object was placed in the commisurotomy patient’s left hand?

the patient could only make wild guesses of what the object was

What do the findings suggest from objects being placed in different hands of the commisurotomy patients?

supports hemispheric lateralisation, shows the left hemisphere is dominant for speech and writing