Inf@Vis!
The Digital Magazine of InfoVis.net

Most of us, when looking at our environment, have the sensation that we are seeing everything sharply. One could say the we perceive our environment in its entirety, that we see everything at once. This illusion is far from reality as we can see by just taking into account that we need to read a book by looking at each word one by one.

To see this better you just need to do a simple exercise: stare at the first word of the next paragraph (ACTIVE) and, still looking at that word, try to read the other one at the other end of the page.

Surprised? Effectively, it's not possible to read the word on the right while we are staring at the one on the left. This is due to the fact that the fovea occupies a tiny area of the retina (a circle of 0.2 mm of diameter) covering only 1% of its surface that, nevertheless, is directly connected to 50% of the visual cortex. The fovea contains a high density of photoreceptors and is responsible fot sharp vision.

What we see and what we don't see. Vision is only sharp in a very small portion around the fixation point whose image falls directly on the fovea. In the images we can see an artistic recreation of the sharp vision area. In the left face we can clearly see the right eye in fovela vision. In the right image we can clearly see the mouth. We can see the eye or the mouth clearly but not both at the same time! The constant movement of the eyes allows us to extract the information we are interested in providing the illusion that we see  it all. Source: Image by Luis Fuentes de Oca. Image treatment by the author. Click on the image to enlarge it.

On the other hand the peripheral retina (the remains of it) with 99% of the surface connects only to the remaining 50% of the visual cortex, integrating the signals of many individual cells into a limited number of neural fibers.

The result is a high visual acuity zone just in the center of the retina (the fovea) and a large peripheral vision area with very low resolution but very sensitive to movement and spatial location....

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