Following a commisurotomy, a split brain patient is undergoing various tests. In
ID: 160431 • Letter: F
Question
Following a commisurotomy, a split brain patient is undergoing various tests. In some experiments, a visual stimulus is presented to either the right or left visual field. In otherexperiments, the patient is asked to reach for objects he cannot see with either his right or left hand. For each of the examples below, indicate what the patient is likely to report seeing or feeling. Explain each of your answers.
A photo of a dog is presented to the right visual field
The patient reaches for a comb with his right hand
A drawing of a house is presented to the left visual field
The patient reaches for a book with his left hand
Explanation / Answer
ANSWER:
After the right and left brain are separated, each hemisphere will have its own separate perception, concepts, and impulses to act. When one split-brain patient dressed himself, he sometimes pulled his pants up with one hand (that side of his brain wanted to get dressed) and down with the other (this side didn't). Also, once he grabbed his wife with his left hand and shook her violently. So his right hand came to her aid and grabbed the aggressive left hand. However, such conflicts are actually rare. If a conflict arises, one hemisphere usually overrides the other.
A photo of a dog is presented to the right visual field
When split-brain patients are shown an image only in their left visual field (the left half of what both eyes take in (see optic tract ) they cannot vocally name what they have seen. This can be explained in three steps: (1) The image seen in the left visual field is sent only to the right side of the brain; (2) For most people, the speech-control centre is on the left side of the brain; and (3) Communication between the two sides of the brain is inhibited. Thus, the patient cannot say out loud the name of that which the right side of the brain is seeing. In the case that the speech-control centre is on the right side of the brain, the image must now be presented to only the right visual field to achieve the same effect.
The patient reaches for a comb with his right hand
If a split-brain patient is touching a mysterious object with only the left hand, while also receiving no visual cues in the right visual field, the patient cannot say out loud the name of that which the right side of the brain is touching. This can be explained in three steps: (1) Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite (contralateral) side of the body; (2) For most humans, the speech-control centre is on the left side of the brain; and (3) Communication between the two sides of the brain is inhibited. In the case that the speech-control centre is on the right side of the brain, the object must now be touched only with the right hand to achieve the same effect.
A drawing of a house is presented to the left visual field
A patient with split brain is shown a picture of a house in separate visual fields and asked to choose from a list of words the best association with the pictures. "Scientists have often wondered whether split-brain patients, who have had the two hemispheres of their brain surgically disconnected, are 'of two minds'". The patient cannot say out loud the name of that which the right side of the brain is seeing.
The patient reaches for a book with his left hand
If a split-brain patient is touching a mysterious object with only the left hand, while also receiving no visual cues in the right visual field, the patient cannot say out loud the name of that which the right side of the brain is touching. Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation the opposite (contralateral) side of the body.
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