Aura, after-images and things like that.
Most of the time our vision works automatically. It adjusts to changing light levels, colours and shapes and movement without us noticing the complex task it is performing. But in certain situations we catch a glimpse of the workings of our visual system:
- Bleaching takes place when you look at something bright - it takes a little while for the 'afterimage' to fade and vision return to normal.
- Look at an object of a bright colour for a while, and then at a white page. You'll see an 'afterimage' in its complementary colour.
- Stare at an object of a bright colour against a blank background for a while and the complementary colour afterimage will appear as an 'aura' at the edges of the object. This is because when you look at something, the eye is actually making small movements.