Do chimpanzees see a face on Mars? A search for face pareidolia in chimpanzees.

We sometimes perceive meaningful patterns or images in random arrangements of colors and shapes. This phenomenon is called pareidolia and has recently been studied intensively, especially face pareidolia. In contrast, there are few comparative-cognitive studies on face pareidolia with nonhuman primates. This study explored behavioral evidence for face pareidolia in chimpanzees using visual search and matching tasks. Faces are processed in a configural manner, and their perception and recognition are hampered by inversion and misalignment of top and bottom parts. We investigated whether the same effect occurs in a visual search for face-like objects. The results showed an effect of misalignment. On the other hand, consistent results were not obtained with the photographs of fruits. When only the top or bottom half of the face-like object was presented, chimpanzees showed better performance for the top-half condition, suggesting the importance of the eye area in face pareidolia. In the positive-control experiments, chimpanzees received the same experiment using human faces and human participants with face-like objects and fruits. As a result, chimpanzees showed an inefficient search for inverted and misaligned faces and humans for manipulated face-like objects. Finally, to examine the role of face awareness, we tested matching a human face to a face-like object in chimpanzees but obtained no substantial evidence that they saw the face-like object as a "face." Based on these results, we discussed the extents and limits of face pareidolia in chimpanzees.