Why some paintings' eyes follow you

A psych prof at Ohio State has used computer graphics apps to determine why some paintings' eyes appear to follow you around the room:

"When observing real surfaces in the natural environment the visual information that specifies near and far points varies when we change viewing direction," he said.

"When we observe a picture on the wall, on the other hand, the visual information that defines near and far points is unaffected by viewing direction. Still, we interpret this perceptually as if it were a real object. That is why the eyes appear to follow you as you change your viewing direction."

Todd said people may be surprised by this phenomenon because of the unique perceptual aspects of viewing a picture. We perceive the object depicted in a painting as a surface in 3-dimensional space, but we also perceive that the painting itself is a 2-dimensional surface that is hanging on the wall.

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(Thanks, Ernie!)