Baboons (Papio papio) spontaneously process the first-order but not second-order configural properties of faces.

A two-alternative forced-choice discrimination task was used to assess whether baboons (N=7) spontaneously process qualitative (i.e., first-order) or quantitative (i.e., second-order) variations in the configural arrangement of facial features. Experiment 1 used as test stimuli second-order pictorial faces of humans or baboons in which the mouth and the eyes were rotated upside down relative to the normal face. Baboons readily discriminated two different normal faces but did not discriminate a normal face from its second-order modified version. Experiment 2 used human or baboon faces for which the first-order configural properties had been distorted by reversing the location of the eyes and mouth within the face. Discrimination was prompt with these stimuli. Experiment 3 replicated some of the conditions and the results of experiment 1, thus ruling out possible effects of learning. It is concluded that baboons are more adept at spontaneously processing first- than second-order configural facial properties, similar to what is known in the human developmental literature.