That is a very interesting observation! When we close both eyes, we perceive a blackness, or perhaps some sort of reddish/purplish glow of light through eyelids, or the after-effect of light. However, by keeping one eye open, it seems any signal from the closed eye is overridden, so you really don't perceive anything there.

Agreed. Definitely just spent a few minutes contemplating if I was seeing anything through my closed left eye. It seemed as if the only way I could turn my left eye "on" when it was closed was by also closing my right eye.

I can differentiate between light or no light in front of my closed eye, even if the other eye is open. Is this the inverse effect of the effect you're talking about?

My brain didn't program itself for vision quite right when I was an infant due to strong nearsightedness at birth so I don't experience this effect.

While the eye which is closed receives – 'less attention' is the best way I can put it – I perceive blackness in that portion of my visual field.

I have the same issue. Two working eyes, but they don't work together properly. I think I can experience the nothingness, but it takes a while to become acclimated, and I can always switch to "looking out" the covered eye.

I've been struggling to comprehend what "nothingness" would look like, but I think this comment has helped. It's very hard to imagine pure blindness.

But that's a question of focus. If you close your one eye and ask "what do I see out of it" you get a different answer than if you don't ask the question.

Yeah, the brain just prioritizes the right eye. If you concentrate you can perceive the blackness in the left eye. That kinda leads me to wonder if eyes send a signal for black? If not and no signal is interpreted as black by the brain and your eyes are damaged then you would "see" black; even if you can't tell it because you have no point of reference?

It's the difference between int(0), None, and undefined :)