split brain research into hemispheric lateralisation

Question 1

Hemispheric lateralisation

Answer 1

the idea that the two halves of the brain are functionally different and that certain mental processes are behaviours are mainly controlled by one hemisphere rather than the other, as in the example of language

Question 2

Split brain studies

Answer 2

SPERRY
- individuals who undergone same surgical procedure - commissurotomy - the corpus callosum and other tissues which connect the 2 hemispheres were cut down the middle in order to separate the 2 hemispheres and control frequent and severe epileptic seizures

Question 3

Procedure

Answer 3

• an image or word could be projected to a patient’s right visual field (processed by the left hemisphere) and the same, or different, image could be projected to the left visual field
• in the ‘normal’ brain, the corpus callosum would immediately share the information between both hemispheres giving a complete picture of the visual world.
• However, presenting the image to one hemisphere of a split brain patient meant that the information could not be conveyed from that hemisphere to the other

Question 4

Key findings - describing what you see

Answer 4

• when a picture of an object was shown to a patient right visual field, the patient could easily describe what was seen.
• if object was shown to left visual field, the patient could not describe what was seen, and typically reported that there was nothing there
• language is processed in the left hemisphere -> patients inability to describe objects in the left visual field was because of the lack of language centres in the right hemisphere

Question 5

Key findings - recognition by touch

Answer 5

although patients could not attach verbal labels to objects projected in the left visual field, they were able to select a matching object from a grab-bag of different objects using their left hand

• objects behind a screen so as not to be seen
• the left hand was also able to select an object that was most closely associated with an object presented to the left visual field
• in each case the patient was not able to verbally identify that they had seen but could nevertheless ‘understand’ what the object was using the right hemisphere and select the corresponding object accordingly.

Question 6

Key findings - composite words

Answer 6

if 2 words were presented simultaneously, one on either side of the visual field, the patient would select a key with their left hand and say the word ‘ring’.

Question 7

Key findings - Matching faces

Answer 7

the right hemisphere also appeared dominant in terms off recognising faces.
When asked to match a face from a series of other faces, the picture processed by the right hemisphere (left visual field) was consistently ignored.
When a composite picture made up of two different halves of a face was presented - one half to each hemisphere - the left hemisphere dominated in terms of verbal description whereas the right hemisphere dominated in terms of selecting a matching picture