The Hollow Face Illusion

This face is actually concave — it curves inward — but your brain often sees it as a normal face projecting outward. Our visual system is so strongly tuned to expect faces to be convex that it can override the depth information from our eyes.

Move from side to side and the face may seem to turn and follow you. The illusion is a striking example of how perception depends not only on what our eyes see, but also on what our brain expects.