Astronomer Carl Sagan argued that perhaps recognizing faces, even in vague shapes, is evolutionarily advantageous.

Joel Voss proposes another explanation: Think of the human brain as a flexible, all-purpose machine meant to succeed in whatever random environment it inhabits. To triumph in strange places, the brain must be able to quickly process unfamiliar visual stimuli—like new shapes and lines—and figure out what's worth paying attention to. Seeing faces and figures is merely a consequence of the brain's tendency to match stored information with new stimuli.

• Joel Voss, a cognitive neuroscientist at Northwestern University, Chicago, is studying how our brains help us ascribe meaning to otherwise random assortments of shapes and lines.
• In studies, he has presented research participants with computer-generated squiggly lines—meaningless sh...