Split Brain!

Could you talk about split-brain patients and how they “see and say” things form each visual field?

I don’t think I can explain it better than this 10 minute video demonstrates.

To appreciate this, try drawing different images with each respective hand like in the video.

Sure. When the corpus collusum is cut, it splits the brain into two hemispheres. Most speech processes occur in the left hemisphere, so whatever information is coming in needs to get to the left hemisphere in order for people to comment. Therefore, the brain can only comment if the information comes in from the right half of the body. As for seeing, you need to focus on the field of vision. Right field of vision will be processed in the left hemisphere and therefore, you can say what you are seeing.

So, pretty much, the two hemispheres of the brain can operate independently of each other. Split-brain patients had their corpus callosum (nerve fibers that connect the hemispheres) severed to control their epileptic seizures. They can describe objects without deficit if presented in the right visual field which is processed on the left, more verbal, side of the brain, but they have great difficulty drawing the image. If the image is presented in the left field visual field which is processed on the right, more visual, side of the brain, the person can draw or choose an object, but they cannot explain it verbally. This is what is now called contralateral processing! Does that make sense?

It’s important to remember why split-brain patients are experiencing what they experience. The human brain is divided between two hemispheres, sometimes referred to as the “right brain” and “left brain.” These two hemispheres communicate via a region of the brain known as the Corpus Callosum. Each hemisphere controls the opposite side of the body!

In approximately 95% of humans, the Broca’s area (which governs the ability to produce language and speech, aka “talk”) is located in the left hemisphere.

In addition to this, you must also remember that the visual field (what your eyes see) is “flipped” after the visual signals from your eyes reaches the thalamus. In other words, what your left eye sees is processed by your right hemisphere, and what your right eye sees is processed by your left hemisphere. To help with this, some students find it helpful to hold their right hand to the left side of their heads, and their left hand to the right side of their head.

Now, for split-brain research!

When the corpus callosum is severed (formerly used as a treatment to prevent epileptic seizures), the two hemispheres of the brain can no longer directly communicate with one another, and must communicate “outside” the body.

Researcher Michael Gazzaniga would flash a word to the right side of the visual field. Remember, this is seen by the right eye, and the signal is processed by the left brain. Normally, because the left brain contains the Broca’s area and can easily say aloud what it sees, this is not an issue. But, for split brain patients, the left brain has no way of receiving information from the right eyeball. As a result, the patient would say “nothing” because that side of the brain has no information to process. However, the left hand might point to an item that represents the flashed word, because the right brain can control the left side of the body.

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