Calculating Vision

This is quite an amazing story. It's on the cover of Nature, from a few days back (3 March 2005). Our brain is constantly involved in figuring out how things actually look like. Not just how they appear to our eyes. This subtle difference is apparent, when one looks at the images shown in the article (pp. 79-83). It's quite a striking effect - I scanned in one image (part of Figure 1).

The rationale given is that our brain is trying to asses the true optical properties of each and every object, and not just pass on the exact image that reaches the retina. So there is a lot of computation going on, which takes into account such things as ambient light, haze and similar things. I guess, these things are more or less 'added to' or 'substracted' from the image that reaches the back of the eye. Our perception is then suitably adjusted, giving rise to what can be 'seen' here above. The circles on the left clearly are dark in tone, whereas we get the feeling that the ones on the right are actually very light. In fact, of course, the circles themselves are completely identical. Yes, I find that hard to believe myself ! But you can check... :)