Monday, April 14, 2014

How We See ? The Eye - Brain Connection

I'm thinking Tal "sees" pretty well ! As far as I know, he incurred no damage to either hemisphere's thalamus, nor to either hemisphere's occipital lobe. But the damage to the right parietal certainly has affected his general understanding of what he sees. No doubt about that. 

In gathering more information about seeing/sight and how our brains process this information, I found an excellent description of the eye + brain = sight in a conversation over on "The Straight Dope"

user njtt offered this overview ..."all talk of the brain, let alone parts of the brain, seeing anything at all is merely loose and metaphorical.  Brains do not see anything, nor does conscious visual experience arise solely because visual information from the eyes arrives at some location in the brain....People and other animals (whole organisms)see things.Their brains play alarge and essential role in the process of seeing, but brains themselves do not see (let alone hemispheres, visual cortices or whatever) 

Much the same could be said of eyes." 

Another user, heavyarms553 offered this explanation of brain anatomy with relation to sight:

"First lets define some words. Medial or nasal means towards the middle, or closer to your nose. Lateral or temporal means towards the sides or closer to your temporal bone.

Lets consider this situations. A doctor shines a light in your eyes on your left side. Light from the light bulb travels to your eyes and hits both of your retinas. Because its coming from the left, it doesnt hit the entire retina on either side. In your left eye, the light hits your medial, or nasal, retina. In your right eye, the light hits your lateral, or temporal retina.

If you look on that diagram, you see that the nerve fibers from both medial retinas cross at the optic chiasm, and continue in the opposite side of the brain. Because of this, information from the left side of both eyes travels to the right brain. Similarly, information from the right side of both eyes travels to the left brain.

So while yes, both eyes are connected to both hemispheres, information from the left and right sides of your visual field go to the right and left hemispheres, respectively.

At the occipital lobe, the rearmost part of the brain, the information received from the retinas is processed, and your brain attributes "what", "where", and "how do I feel about this" to the things that you see. Without the occipital lobe, your brain can't understand the information it receives. Losing the occipital lobe is sort of like trying to stream a video with the wrong codec. You get all the raw information, but you have no way to interpret it.

Interestingly, lesions of the occipital lobe can cause a phenomena known as cortical blindness. Patients will swear up and down that they can see just fine, but will be unable to tell you what they are seeing. You can predict what areas of their visual field will be affected by the extent of the lesion.

So yeah, that diagram explains it all pretty well. The corpus callosum is not involved with vision until after it has been processed by the occipital lobe."

So where does that leave Pop? 

As I understand it with "sight" ! But perhaps not insight

Again the missing right parietal means that interpreting information in his left visual field is indeed lost or not possible. Any way around that? Another path to be developed and explored ? 

One more piece of the puzzle to work out!  

Tal's daughter,

No comments:

Post a Comment