Something odd I noticed.

[Dayman]

Why do small points of light (i.e., stars), look brighter when I'm not focusing on them?

[TheKwas]

Your blind spot is in the exact center of your pupil, and since stars are such tiny objects in your field of vision you'll often seen them better if you don't look directly at them. Astronomers (according to Carl Sagan at least, if I remember correctly) will often do this when looking at stars with the naked eye.

[Juvenal]

There are two types of light-sensitive cells in the retina - rods and cones.

Cones are responsible for colour vision (there are three varieties each most sensitive to the wavelength of one of the primary colours red, green, blue).

Rods only give monochrome vision.

Rods are distributed across the whole retina, but the cones are grouped around the centre of vision (the Fovea).

Rods are more sensitive than cones, this is why night vision is monochrome, and it also explains why stars appear brighter out of the corner of your eye since there is a greater proportion of rods there - hence greater sensitivity to dim light sources.

@TheKwas - the blind spot is not at the centre of vision, it is slightly off to the side. The classic demonstration of this is to hold the index fingers of both hands up together, and look at one while you move the other slowly away sideways. There will be a region where the moving finger disappears then reappears.

[Ummon]

Rods are more sensitive than cones, this is why night vision is monochrome, and it also explains why stars appear brighter out of the corner of your eye since there is a greater proportion of rods there - hence greater sensitivity to dim light sources.

There is also a higher Rod per gangliar cell ratio faraway from your retina's center. Therefore you have a higher chance to have potentials from low light intensities.

[TheKwas]

Turns out I'm full of malarky. Could have sworn I heard that somewhere.

[Richard]

I often notice this in my bedroom, staring at something directly will render it invisible. I can't see what beasts lurk in the corner behind my half-closed door if I look directly at it.

[Juvenal]

...staring at something directly will render it invisible.

That is a different aspect of how vision works. In the visual cortex at the back of the brain, there are many small areas of cells that function as detectors for various geometric features.
For instance there might be a region that recognises vertical lines in the bottom left of your visual field, another that recognises blobs just above the centre of vision etc, etc.
The brain constructs what we think we see by integrating the responses from all of these areas.
These regions only fire when the feature they recognises moves across their part of the visual field. This isn't usually a problem, because the eyes are normally in constant motion - moving, fixating and moving again (like the way that pigeons heads move when they walk). However, if you stare at something and consciously keep your eyes still, then the recognition areas stop firing and you find that can can see very little in the way of features (you can't stop your eyes completely, so the world doesn't actually disappear).

[Beiss]

The index finger thingy doesn't seem to be working for me. What kind of backdrop would you recommend? How far away from my face should I hold my fingers?

[Gwendylyn]

Beiss,

http://www.blindspottest.com/

Press the next button and play.

[Beiss]

Ah, yes, that worked better. My, how big the spot was the dot was gone for a pretty long time, and I even saw it eclipsing like the moon does.

[Spurius]

Juvenal, you have any picas of how we actually 'see' things before it's processed by the brain. Used to have loads of those, but can't find them. Meh.

Is *real* weird, like fish-eye, and we cannot really see everything at the same time etc.

Beiss, I suppose the 'eclipse' effect is one blind spot in one eye 'just' not overlaying the other?

[Juvenal]

Juvenal, you have any picas of how we actually 'see' things before it's processed by the brain.

It took a lot of trawling, but finally I found this...

At http://sharp.bu.edu/~slehar/webstuff/consc/consc.html

The fact that the image projected on the retina is distorted is not really relevant - after all we aren't looking at that image with another "eye". In actual fact we only see in detail with the fovea and everything else is peripheral vision.

Anyhow, the brain corrects the distortion of the picture in the same way that it compensates for the fact that the projection onto the retina is actually reversed!

Also, as Ummon said cones are each connected to a single bipolar cell (the cells that generate the signal that goes to the brain), whereas multiple Rods share the same bipolar cell. This means that colour vision with Cones has higher resolution, and monochrome vision with Rods is more sensitive.

[Beiss]

Yeah, just looking with one eye, Spurius.

[Spurius]

Sorry to be unclear, I was just wondering if that eclipse effect was due to the distance between our two eyes, and those blind spots not exactly overlapping.

Mmm. One eye too. Got to try that, then.

[Beiss]

I don't really understand why the brain flips what we see up-side down so it's right again - if we were born viewing everything upside down, we'd get used to it anyway, wouldn't we?

[Spurius]

You can put on glasses that turn everything upside-down, in 48 hrs everything will be normal again - until you take the glasses off, and then you will have to readjust another 48 hrs to get back to normal, IIRC.

The brain can apparently accomodate for it.

[Beiss]

Hahah, I'd like to try glasses like that. It'd be cool to make a movie in well-known places, but where everything (except text) is mirrored, to confuse people. They will know where they are, but not quite... I was totally braincrashed when I had started playing Twilight Princess on a Wii, only to start over again from the beginning on a Gamecube (it's the exact same game, but everything is mirrored).

[Spurius]

Try Prey - FPS where you can walk the ceilings in some levels. Has OBE too (you can leave your body, and let your spirit fight). Real weird at first, but fun.

[Beiss]

Tried it. Was fun at first, but weird.

[Spurius]

Yeah well, YMMV (your mouse may vomit, too).