First- and second-order configural sensitivity for greeble stimuli in baboons.

Previous studies on nonhuman primates have shown inconsistencies in their processing of first- and second-order relational properties of facial stimuli. Using greeble stimuli sharing configural properties with faces, this study assessed configural processing in baboons. Five baboons were trained to recognize a positive stimulus among pairs of greebles in a two-alternative forced choice task. They were then tested with new stimulus pairs involving either a first-order version, with modifications in global qualitative spatial relations, or a second-order version, with modifications of finer spatial relations. Performance remained above chance in all test conditions, including when only second-order cues were available, but it was higher for first-order trials. It is proposed that an extensive training with greebles led to the processing of second-order relational properties. These results demonstrate that configural sensitivity is not restricted to faces in baboons and suggest that a common mechanism may support configural processing for face and nonface stimuli.