Shadowing can provide a cue for depth.For example,if a shadow appears on the bottom of a circle,the object appears convex.However,if the shadow appears on the top of the object,it appears concave.This happens because

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In the real world, light sources tend to come from above more often than from below, so we have evolved to interpret shadows on the bottom of an object as being cast by a light source above, which cues us to perceive the object as convex. Shadows on the top of an object are interpreted as being cast by a light source below, cueing us to perceive the object as concave. Our ability to interpret shadows in this way is therefore a result of our evolutionary history, not of dedicated brain areas or learned knowledge.

Shadowing Can Provide a Cue for Depth