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I know from my direct experience that it works,

Direct personal experience is good to coin questions, not to produce validated knowledge.

== Sound: My "direct personal experience" tells me there is a constant high pitch sound in my environment. Knowledge tells me it is Tinnitus https://en.wikipedia.org/wiki/....
== Sight: My "direct personal experience" tells me I see phantoms right now. Knowledge tells me these are floaters https://en.wikipedia.org/?titl....
== Taste & Smell: My "direct personal experience" tells me I am eating a peach. Knowledge tells me I smelling a peach, while biting and shewing an apple.
== Taste: My dad's "direct personal experience" tells him this peach has no taste at all. Knowledge tells him he is suffering Ageusia : https://en.wikipedia.org/wiki/...
== Touch: My "direct personal experience" tells me I have pins and needles on my arm. Knowledge tells me I have a kind of nerve anesthesia.
== Sight: Through "direct personal experience", billions of individuals believed earth is flat. Knowledge tells us it is spherical.
== Sight: Through infinitely reproducible "direct personal experience" billions of individuals - including you right now -, across many centuries, across many civilizations, every where on the planet can drop a pen in a glass of water and believe it is broken. Knowledge tells us the refraction of light leads us to believe so.

See for yourself what your "Direct personal experience" tells you for example there on first Google hit on "optical illusion" : http://www.michaelbach.de/ot/

Not a single sens we have can be trusted to produce knowledge. Not mines. Not yours. This is basic knowledge. At 18 years of age, school should have informed you about objectivity and subjectivity.

Well, the best explanation is that our brain does very, very hefty colour correction on its own. The reason is probably so we can ignore the irrelevant information, i.e. the light colour and any sensitivity lag between the different cones and identify objects.

If you've ever tried to do colour computer vision you will be *astonished* at how good we are at it.

Anyway, my guess is that the reason for this one appearing as two different things is it's very close to some threshold. It's possible to interpret it as more or less normal colours under a blueish light (i.e, sunlight), which makes you perceive the blueish grey as white. Or, you perceive it as blue under washed out much more orange light (e.g. incandescent bulbs) in which case you perceive the blueish grey as blue. The "white/blue" colour is objectively blueish grey if you check the actual hex values: it's mostly grey but the blue channel is a bit higher, but not by that much.

Our brains seem to model the complete co varying of the colours so once you decide what the light colour is, this effects the perception of all the colours. Black is nevertruly black and always reflects some light, so once the brain has decided the blue is super washed out by excessive light and that light is orange, that makes bright orangish things perceived as black since that's how black would appear under those circumstances. Given the rather good corrections of the picture, it appears those people are correct (though I'm on the white/gold side).

These two perceptions are very, very different and so it's kind of a binary thing, either you perceive one or the other. Now, I suspect that this photo is very close to the tipping point which is why some people perceive it very differently from others.

Either way, it's a fascinating example of colour interpretation.

This one is also excellent:

http://en.wikipedia.org/wiki/F...

http://www.michaelbach.de/ot/c...

The Freiburg Vision Test (‘FrACT’) may be a start.

Quote: "The “Freiburg Vision Test” encompasses the “Freiburg Visual Acuity & Contrast Test” (FrACT) and Vernier Test to assess acuity and other visual functions. It is a free computer program that uses psychometric methods combined with anti-aliasing and dithering to provide automated, self-paced measurement of visual acuity (Bach 1996), contrast sensitivity and vernier acuity ..."

http://www.michaelbach.de/fract/index.html

CC.

the very concept of "illusion" implies that I had a choice

No, illusion is when perception does not accurately reflect reality. It does not imply choice. Take the Hering Illusion for example. The red lines appear to be curved even though they are actually straight. We don't choose to see the lines one way or the other. That's just the way we see them.

Of course it's obvious that we have free will. We make hundreds of choices every day. But the fact that free will is obvious does not eliminate the possibility that it could be an illusion.

This and this are more interesting to me - the after-image of the animated pattern distorts anything you look at for a few second after you stop looking. The rotating snakes one is cool too though. :)

This and this are more interesting to me - the after-image of the animated pattern distorts anything you look at for a few second after you stop looking. The rotating snakes one is cool too though. :)

The second article contains a slide-show of various illusions [CC] [GC] and why the brain interprets them as it does.

Maybe I missed something, but I found the second article to be a let-down.

(Warning for epileptics: if visual stimuli can set off a seizure for you, you should probably stay away from the following links. I am not susceptible, but I found the second link to be visually overwhelming at first.)

IMHO, more interesting galleries of examples can be found at Wikipedia's Optical Illusions page and at Michael Bach's 78 Optical Illusions & Visual Phenomena page.

See http://www.skepdic.com/pareidol.html for a definition. A commentary on this particular image (along with some wicked cool visual illusions) is at http://www.michaelbach.de/ot/fcs_face_on_mars/inde x.html

Please excuse me, I have to return to searching my toast for the Virgin Mary now.

Some sites have great explainations and demos.

This has nothing to do with image sensors, but does have some bearing on "what can eyes really see".

Isn't the human brain programmed to see faces?

I would have never thought it was true until i saw this web page

http://www.michaelbach.de/ot/fcs_hollow-face/index .html

Check it out, pretty amazing stuff.

Oddly enough, someone sent me one of the examples from that page a few days ago, and I dug around until I found it. :)

I was familiar with most of the examples. One that I hadn't seen before was Troxler fading example.

http://www.michaelbach.de/ot/col_rapidAfterimage/i ndex.html

Awesome site. This one still blows me away every time.

So what you are saying is that this "Moon Illusion" is simply an occipital lobe processing error? Makes sense to me, there are obviously intances where our brain is incapable of properly processing information. This was the first hit on google. I recommend trying the full tour, its neat stuff.

-kaplanfx

Michael Bach's page has most of these illusions and more in interactive flash.