Steven Pinker in his book 'How the mind works' says:

our conscious sensation of color and lightness matches the world as it is rather than the world as it presents itself to the eye. The snowball is soft and wet and prone to melt whether it is indoors or out, and we see it as white whether it is indoors or out. The coal is always hard and dirty and prone to burn, and we always see it as black.

and then on the samepage he gives an example that, to me, seems to prove the exact opposite:

When a television set is off, the screen is a pale greenish gray. When it is on, some of the phosphor dots give off light, painting in the bright areas of the picture. But the other dots do not suck light and paint in the dark areas; they just stay gray. The areas that you see as black are in fact just the pale shade of the picture tube when the set was off. The blackness is a figment, a product of the brain circuitry

We see black when it IS pale greenish grey. what am i missing here?

  • $\begingroup$ I think he is referring to top-down processing. It's the same phenomenon that causes the gold/blue dress illusion, among others. This is about how hard our brain works to guess the object's true color, rather than just using the color that reaches our eyes. $\endgroup$
    – Arnon Weinberg
    Jul 9 at 17:15

The two paragraphs are saying the same thing; I think Pinker is making a bit of a grandiose philosophical statement in the meaning of "the world as it is", but it makes sense if we give that the narrow meaning he's actually using: the "world as it is", the color of an object, refers to how that object reflects light. Not the spectrum of light emitted, which changes by the ambient light available, but how the object changes the ambient light spectrum to reflect just part of it.

The distinction he's making is in the difference between perception and the actual signal entering the eye; alternatively, think of that signal as what one pixel from a digital camera would register. Perception will be constant ("match the world as it is"), while the camera pixels would register something very different for the same object in different contexts.

A white snowball reflects light the same whether it's inside a candlelit room or out in the bright sun, but because the light source is different you will receive a completely different spectrum and intensity of light at the eye (or camera) in those two settings. However, the perception of the snowball being white stays the same. It stays the same because you aren't directly reading the count of photons of different wavelengths coming off the snowball to decide it's white, you're making comparisons with all the other light coming off all the other objects in the room to determine how much ambient light there is, and based on that, which wavelengths each object in the room must be reflecting ("the world as it is").

The TV example is the same, just from a different perspective. You're perceptually making the same "ambient light" corrections as the candlelight/sunlight distinction, except in this case for the emitted light of the TV. If, say, the TV is showing a picture of a car driving down an asphalt road, the asphalt is black and you perceive it as black even if there is actually the pale greenish gray light entering the eye.

  • $\begingroup$ If we see a snowball in a room with only red lights, wouldn't it appear reddish instead of white? $\endgroup$
    – Gull Noor
    Jul 9 at 16:47
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    $\begingroup$ @GullNoor Certainly not if merely reddish; candlelight, as my example, is reddish compared to say, sunlight. Usually you can buy light bulbs in at least "warm" or "cool" these days, where the former is reddish and the latter is blueish. With truly red lighting, then you'd certainly detect that the room is red overall, and sense that things look abnormally red, but you'd clearly identify that this is because the lighting is red, not perceive the the snowball changed it's intrinsic color. At least thats my experience with red lighting. $\endgroup$ Jul 9 at 16:52
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    $\begingroup$ Actually probably the best example I have personal experience is in a red light room used to house rodents without resetting their circadian clocks. If someone asked you to go pick up a white rat in that room you wouldn't hesitate. You would detect that, sure, it's a bit pinkish because of the extreme lighting, but it definitely wouldn't look "red". $\endgroup$ Jul 9 at 16:55

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