Depth reversal

This face mask from the former tennis player Björn Borg appears convex (protruding) but is actually concave (pointing inwards).

A depth inversion ( Hollow-Face-Illusion ) is an optical illusion that allows us to perceive three-dimensional protruding faces, although in reality an inwardly curved structure prevails. A concave therefore face mask appears with proper lighting as a convex structure (see picture right). The opposite effect (a convex structure appears concave) can also be observed. Another effect of the depth reversal occurs in the case of actually planar images, into which the observer can interpret both a convex and a concave structure and, with a little practice, can let the interpretation "jump around".

Explanation

The image of the face mask displayed on the retina can be interpreted ambiguously (either as a foreground or a background). The human brain automatically chooses the more likely interpretation. Since we are used to meeting faces in everyday life, the mask background is also interpreted as a face. This example shows that our perception is often based on experience.

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This picture clearly shows how both the front and the back of a mask are perceived as a protruding face at a certain point.