A couple of months ago I remarked on the misformatted picture of Saddam Hussein:
What is interesting is that the distorted image is still recognisably Hussein. The image processing and facial recognition circuitry in the human brain is truly an amazing thing.
You see this time and again. A home theatre projector works by convincing the brain that the white screen is actually black in parts. The contrast between the brightly projected colours and whites, and those areas masked by the LCD panels or whatever into ‘black’, is expanded by the brain over time so that ‘black’ soon becomes, as far as perception is concerned, black. Likewise, if you see a white cat in a dully-lit room, it will still look white, even though its objective brightness is may be less than the grey blacks produced by an LCD projector.
Our sensory systems have evolved not to give us accurate absolute measurements, but a useful perception of the world around us. That means being able to recognise things in a wide range of circumstances. So that white cat is recognisably white at most light levels, regardless of the background (the exception is where the light level is so low our sight effectively fails).
Likewise, our sight systems include an auto-white-balance system like those in digital cameras. That’s why everything looks normal under incandescent lighting, but if you take a 35mm picture under such lighting on a regular film, the print looks orange (blue-green for fluorescent lighting).
FuturePundit blog has an interesting item on this. A small quote:
The mind has the capability to create an interpreting facility to map between what it sees and how it perceives what it sees. This allows the mind to adjust for the effects of bifocals and other sense-distorting factors. While this capability is adaptive it can sometimes be tricked into creating erroneous interpretations of sensory input.