Sunday, June 29, 2008

Eyesight

I just came back from looking at the sky in the middle of nowhere at 7000 feet of altitude, no moon. Fantastic. And... I did an experiment.

Pick a star that is brighter than the average, and focus your eyes on it. Do not move your eyes and do not blink. After a while, everything starts fading away. Maybe you lose track of your star. But keep still and do not blink. Hold that for about 30 seconds. Then, without moving your eyes, blink.

You are now aware of many more stars than you were before starting. The dark blue looks lighter, and you can also feel as if the sky is really a fabric rich with bright dots. It almost appears as if it was a piece of cloth with texture.

Then, your eyes move ever so slightly and you're back to "normal".

Why does this happen? Is the fade out some "dead pixel removal" done by the brain, which later realizes what's going on and finally let's you see the long time exposure photo in your retinas?

In any case, it can be quite a surprise to get, for the briefest of moments, a much more clear picture of how many stars are really out there. Beautiful.

5 comments:

Rob Vens said...

Vision is really a very interesting phenomenon. It has very little in common with what most people think vision is: a lens (the eye), a sensor (the retina), and a computer (the brain). What in fact seems to happen is that the brain "infers" the reflection of the outside world inside us from a flurry of images, or maybe more accurately: the differences between two subsequent images. This can easily be demonstrated from your experiment: keep the eyes focussed (completely still is impossible but you can approximate that as much as you are able) and the image start to blur, until you can become almost blind. Then move, and suddenly you "see" again. The eye can be seen to move constantly, to shift focus very briefly (fractions of seconds) almost like Brownian movement of particles. Vision is not static.

Andres said...

Rob,

Sometimes I've wondered if optical illusions are symptoms of the brain's optimizations for the process of vision. In other words, if you took optical illusions away, would vision be adversely affected? And if so, how? Do you know if this has been researched?

Andres.

Carl Gundel said...

In addition, the retina is not just a sensor. It actually is a part of your brain in a way because it processes visual information before sending through the optic nerve. Fascinating stuff.

Rob Vens said...

I am not sure about "optimisations" but certainly vision is generally a brain product in which the eye itself plays an important but secondary role. There is an interesting experiment with glasses that turned vision upside down. After a few awkward days the subjects report a sudden return to normal vision. They would see the world straight up again.
Back to optical illusions...how would you "take them away"?

Andres said...

Rob,

I am not sure how to take optical illusions away. However, sometimes I wonder if they are not symptoms of the implementation the nerve system chooses to do its work. If there was a switch and we could turn them off, then we might be able to learn more about what the brain is doing. Nevertheless, I have to say I have not studied the topic as much as I'd like to make that kind of statement/suggestion based on something :).

Andres.