Perceptual illusions are not only great fun, they also remind us of a basic truth: Our perceptions are more than projections of the world into our brain. As our brains assemble sensory inputs they construct our perceptions, based partly on our assumptions. When our brain uses rules that normally give us accurate impressions of the world it can, in some circumstances, fool us. And understanding how we get fooled can teach us how our perceptual system works.
A case in point is the famed Müller-Lyer illusion, for which the Italian visual artist Gianni Sarcone gives us two wonderful new examples.
Many more informative examples can be found amid the 644 pages of the new Oxford Compendium of Visual Illusions. There I discovered a fascinating phenomenon reported by Gettysburg College psychologist Richard Russell.
First (with Professor Russell’s kind permission from his earlier article in Perception) a question:
In the pair of Caucasian faces, below, which looks to be the male, and which the female?
Do you (as did I) perceive the left face as male, the right face as female?
Many people do, but in actuality, they are the same androgynous face (created by averaging Caucasian male and female faces), but with one subtle difference: the researchers slightly darkened the skin (but not the lips or the eyes) in the left face and lightened the skin in the right face. Why? Because worldwide and across ethnic groups, Russell and others report, women’s skin around the lips and eyes tends to be lighter than men’s. And that means more contrast between their skin and their lips and eyes.
That natural, subtle facial sex difference enabled Russell to recreate what he calls “the illusion of sex” with a second demonstration. This time, he left the skin constant but lightened the lips and eyes of the left face, making it appear male, and he darkened the lips and eyes of the right face, increasing the contrast, making it appear female.
Russell suggests that this helps explain why, in some cultures, women use facial cosmetics. Lipstick and eye shadow amplify the perceived sex difference, he notes, “by exaggerating a sexually dimorphic attribute—facial contrast.”