Credit: LEFT: P. THOMPSON PERCEPTION 9, 383–384 (1980)/PION, LONDON; RIGHT: B. BASILE/YERKES NATL PRIMATE RES. CENTER

Curr. Biol. doi:10.1016/j.cub.2009.05.067 (2009)

The human talent for recognizing differences in faces relies on how facial features are configured. But flip an image of a face, and alterations as drastic as inverted mouths and eyes aren't as noticeable — a phenomenon known as the Thatcher effect. Robert Hampton of Emory University in Atlanta, Georgia, and his colleagues recently demonstrated that the effect is present in another primate.

They monitored the length of time rhesus monkeys (Macaca mulatta) looked at pictures of monkey faces. Over time, the animals became less interested in all images, but they spent significantly more time looking at the strange, upright altered (Thatcherized) photos than they did looking at the same images upside down.