To find out whether monkeys experience face pareidolia, the scientists studied five rhesus macaques in the lab. During the experiments, each monkey saw pairs of images on a computer screen. The pairs included 45 different photos in every possible combination. Fifteen of the photos were the kinds of pictures that might appear on Faces in Things: frightened bell peppers, a shy kiwi fruit, and so on. (A separate group of human subjects had confirmed that these objects looked like faces.) Fifteen more photos were matched images that didn’t look like faces: regular peppers, a featureless kiwi. And the remaining pictures were the real faces of rhesus macaques. […]
The macaques in the study spent more time looking at face-like objects than at ordinary objects—or at the actual faces of monkeys. They especially focused their gaze on the “eyes” and “mouths” of the illusory faces. The results were so consistent that a computer program could predict from a monkey’s eye movements whether it was looking at a fake face or its matching faceless object.
The authors think the best explanation for their results is that macaques experience the same illusion we do. “The underlying cause of this illusion is most likely common to both humans and rhesus monkeys,” they write.