Chapter 48. Visual Fields and Hemispheres

Learning Objectives

cerebral cortex
six thin layers of interconnected neurons that cover the outer surface of the brain and do most of the brain's processing
contralateral
opposite side; each brain hemisphere receives contralateral sensory signals and exerts contralateral control of movement
corpus callosum
band of neural fibers carrying messages between hemispheres
epilepsy
a neurological disorder associated with abnormal synchronized electrical activity in the brain, which can produce seizures
hemisphere
one half of the brain; divided into four lobes
split-brain patient
person whose corpus callosum has been cut as a treatment for severe epilepsy
visual field
the portion of the visual environment that falls to the left or the right of the point where the eyes are focused
Visual Fields and Hemispheres
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Learning Objectives:

Understand the relationship between the eyes and the visual fields.

Identify which brain hemisphere receives the visual information from the left and right visual fields.

Predict how a split-brain patient would respond to information presented to one visual field.

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The image is a vertical cross section through the middle of the brain to show the back of the brain. The left side of the brain or the left cerebral cortex is labeled the left hemisphere. The right side of the brain or the right cerebral cortex is labeled the right hemisphere. A band of fibers connects the two hemispheres in the center of the brain. This is called the corpus callosum.

1. The cerebral cortex of the brain is divided into two hemispheres, each hemisphere communicating with the other through a large band of fibers called the corpus callosum.

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The image is a figure of the human body. A purple arrow goes from the left hand up to the neck, where it crosses over to the right hemisphere of the brain. A red arrow goes from the right hand up to the neck, where it crosses over to the left hemisphere of the brain.

2. The hemispheres are connected to the opposite (contralateral) side of the body. So, the right hemisphere receives sensory input from the left side of the body (as shown here in purple), and controls the muscles on the left side of the body. The left hemisphere receives input (the red arrow) and sends control signals to the right side of the body.

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The image is a top view of the brain. In front of the brain is a visual field. Images from the left visual field travel to the back of the eye on the right side. These then travel down the optic nerves from both eyes to the right hemisphere of the brain. Images from the right visual field travel to the back of the eye on the left side. These then travel down the optic nerves from both eyes to the left hemisphere of the brain.

3. The hemispheres do not receive visual input from the contralateral eye, but instead receive input from the contralateral visual field. A word flashed briefly in the left visual field would go to the right hemisphere, and vice versa—regardless of which eye is being used.

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The image combines the faces of two people into one face. The left side of the image is the left half of a man's face and the right side of the image is the right half of a woman's face.
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4. Stare at the nose of the person in this photo. Is the person a man or a woman? Because the male half-face is in your right visual field, your left hemisphere thinks the person is a man—but your right hemisphere thinks the person is a woman!

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There are two images on the screen. The first image combines the faces of two people into one face. The left side of the image is the left half of a man's face and the right side of the image is the right half of a woman's face. The second image is a top view of the brain. In front of the brain is the first image of the combined faces. The man's face from the left visual field travels to the back of the eye on the right side. This then travels down the optic nerves from both eyes to the right hemisphere of the brain. The woman's face from the right visual field travels to the back of the eye on the left side. This then travels down the optic nerves from both eyes to the left hemisphere of the brain. Arrows show the transfer of information between the two hemispheres through the corpus callosum.
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5. For people who have a normal corpus callosum, it doesn't really matter which hemisphere directly receives the information, because the information is quickly shared with the other hemisphere. Both hemispheres are immediately aware that the person in this photo has a strange appearance.

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There are two images on the screen. The first image demonstrates the process that occurs when someone has a normal corpus callosum. The image is a top view of the brain. In front of the brain is an image combining the left half of the face of a man on the left with the right half of the face of a woman on the right. The man's face from the left visual field travels to the back of the eye on the right side. This then travels down the optic nerves from both eyes to the right hemisphere of the brain. The woman's face from the right visual field travels to the back of the eye on the left side. This then travels down the optic nerves from both eyes to the left hemisphere of the brain. Arrows show the transfer of information between the two hemispheres through the corpus callosum. The second image demonstrates the process that occurs when someone has a severed corpus callosum. The image is similar to the first image of someone with a normal corpus callosum except that information does not transfer between the two hemispheres. The corpus callosum is severed, thus information cannot cross to the other hemisphere.

6. But in the case of split-brain patients, who have had their corpus callosum cut as a way of treating severe epilepsy, the information remains locked in the hemisphere that first received it.

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There are two images on the screen. The first image shows a person sitting at a desk with a screen in front of them. A face is flashed briefly to the right visual field on the screen. The patient is asked to report what he saw. An arrow shows the face image traveling to the left hemisphere. The left hemisphere knows what it saw, but can't share that with the right. The patient says he saw a face because the left hemisphere can speak. The second image shows a person sitting at a desk with a screen in front of them. A face is flashed briefly to the left visual field on the screen. The patient is asked to report what he saw. An arrow shows the face image traveling to the right hemisphere and down the person's left arm. The right hemisphere knows what it saw, but can't share that with the left. The patient says he saw nothing but the left hand draws a face.

7. Because the left hemisphere usually controls language, split-brain patients can only speak the information if it goes directly to the left hemisphere, as shown in the illustration. If the information goes directly to the right hemisphere, the person can’t speak the name of the object, but can draw it with the left hand (controlled by the right hemisphere).

Practice 1: Connected Hemispheres

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Practice 1: Connected Hemispheres

Play the animation to review information about the two hemispheres.

Practice 2: Contralateral Sensory Connections

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Practice 2: Contralateral Sensory Connections

Read the description, then select one of the brain hemispheres to indicate your answer.

Let's see if you understood the point about contralateral (opposite-side) connections to hemispheres.
If a person's left hand is touched, which hemisphere receives that sensory information?
Think about this, and then select the appropriate brain hemisphere to indicate your answer.

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Practice 3: Split-brain Experiments Using Touch

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Practice 3: Split-brain Experiments Using Touch

Play the animation to review the results of split-brain experiments when patients explore objects with their hands.

Practice 4: Split-brain Experiments Using Vision

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Practice 4: Split-brain Experiments Using Vision

Play the animation to review the results of split-brain experiments when patients view words and objects on a screen.

Quiz 1

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Quiz 1

Indicate where the visual information would flow by dragging each object to the gray area near the appropriate hemisphere. When both the objects have been placed, select the CHECK ANSWER button.

The image is a top view of the brain. Images from the left visual field travel to the back of the eye on the right side. These then travel down the optic nerves from both eyes to the right hemisphere of the brain. Images from the right visual field travel to the back of the eye on the left side. These then travel down the optic nerves from both eyes to the left hemisphere of the brain. In front of the brain are two pictures. The picture on the left is a cup, while the picture on the right is a key. key cup
Perhaps you should go back to review the relationship between the eyes and the visual fields.
Select the NEXT button and move to Quiz 2.



Cup



Key

Quiz 2

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Quiz 2

For each person, select one of the buttons to indicate Probably yes or Probably no in answer to the question.

Individuals with normal brains could speak the word, but split-brain patients could not, because the information never gets to the left hemisphere. Select the NEXT button and move to the Conclusion.
You did not select the correct answers. Try again.

The two people represented below are both right-handed individuals with normal intelligence. If the word “cat” is flashed to the left visual field (LVF) of both individuals, will they be able to speak the word aloud?

Probably yesProbably no Probably yesProbably no
There are two images on the screen. Both images have a top image of the brain showing the optic nerves leaving the eye and connecting to the two hemispheres. The word 'cat' appears on the left visual field for each brain and in right hemisphere of both brains. first image is a split-brain patient with corpus callosum missing. The second image is a person with a normal callosum connecting the two hemispheres.

Conclusion

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