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Cosmic rays can cause optical flashes, but it tends to happen only when you're outside the earth's magnetosphere, which blocks most of the culprit rays. You haven't been in outer space lately, have you?http://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena
I have noticed that when i close my eyes it's not just pure black I see (even in the absence of light) but some kind of "ocular noise" !! ...
Quote from: neilep on 14/09/2012 20:34:15I have noticed that when i close my eyes it's not just pure black I see (even in the absence of light) but some kind of "ocular noise" !! ...https://en.wikipedia.org/wiki/Phosphene [ which blind people can experience if they were previously sighted ]https://en.wikipedia.org/wiki/Visual_snow
There is also a transient effect when you first close your eyes.Our eyes have an exquisite automatic gain-control system that lets us see inside the house and outside through a window at the same time - to achieve the same effect, cameras have to take multiple exposures using "High Dynamic Range" techniques.But when we first close our eyes, this ocular system takes a few seconds to adapt, so we see "echoes" of the previous scene for a few seconds.
The nerves in our retina are unusual in that they operate in "analogue" mode, sensitive to the smallest disturbance from light. It is always on the verge of generating a nerve impulse, and it will always generate a small "false positive" rate.This means that your retina is always consuming energy at a high rate, which is why "tunnel vision" is one of the first symptoms of hypoxia.Most nerves in our body operate in "digital" mode, propagating signals in an ON/OFF manner, and consuming the most energy only when firing. It is a well-known advantage of digital transmission that it does not amplify or propagate noise to the same extent as analogue mode. http://en.wikipedia.org/wiki/Claude_Shannon#Postwar_contributions
... So, our eyelids are just like lens covers but in our case the "camera" is always turned on !!
Blinks profoundly interrupt visual input but are rarely noticed, perhaps because of blink suppression, a visual-sensitivity loss that begins immediately prior to blink onset. Blink suppression is thought to result from an extra-retinal signal that is associated with the blink motor command and may act to attenuate the sensory consequences of the motor action.