Seeing Illusionary Faces

Rhesus monkeys viewed photos of objects with illusory faces (top) and similar objects without illusory faces (bottom). The overlaid color maps show where monkeys fixated their gaze when viewing the photos, with higher peaks and warmer colors indicating longer fixation times.

Jessica Taubert

Pareidolia is the common human experience of perceiving a pattern where there isn’t one, like seeing faces in inanimate objects. Humans, it turns out, are not the only species to experience this phenomenon.  According to a new study, rhesus monkeys (Macaca mulatta) do, too. 

An international team of researchers at the National Institute of Mental Health in Bethesda, MD and at Macquarie University in Sydney, Australia, gathered photos of inanimate objects that elicited face pareidolia, such as a cup of coffee in which the foam bubbles look like a smiling face, and similar photos that did not, such as a regular, faceless latte. They showed these photos, along with photos of other monkey faces, to five rhesus monkeys while recording the monkeys’ eye movements. The monkeys looked significantly longer at photos of monkey faces and illusory face-objects than at photos of normal objects, indicating that the monkeys found both real and illusory faces more interesting than faceless objects. 

Additionally, researchers found that monkeys tended to fixate their gaze on the “eyes” and “mouths” of not only the real monkey faces, but also the illusory faces. This suggests that monkeys did indeed perceive the inanimate objects as having faces. “Rhesus monkeys, and in fact all primates, are social animals and, like us, they need to access information in the faces of their friends, family, or enemies to judge how to behave,” says Jessica Taubert, a neuroscientist at the National Institute of Mental Health and lead author of the study. “Faces are extremely important sources of social information for primates because they signal expression, mood, gender, age, health (fertility), kinship, and attractiveness.” 

Rhesus monkeys, like humans, have cognitive mechanisms to quickly recognize faces—even if that system generates some false positives, such as finding a smiling face in the foam of a cup of coffee. (Current Biology)