The face inversion effect in non-human primates revisited – an investigation in chimpanzees (Pan troglodytes)
A face presented upside-down is harder to recognize than presented right-side up. This deterioration in recognition is known as the face inversion effect, being stronger in faces than objects. With inversion the perceptual processing of the spatial relationship among facial parts, which is a major source of information to discriminate faces, is disrupted. Previous literature indicates a face inversion effect in chimpanzees (Pan troglodytes) toward familiar and conspecific faces. These results are consistent with findings from humans, however methodologically controversial. In the present study, we tested captive chimpanzees in a delayed matching-to-sample task with chimpanzee and human faces and replicated a deterioration of performance scores by inversion. More interestingly, we found that the discrimination deterioration was systematically different between the two age groups of chimpanzee participants, i.e. young chimpanzees showed a stronger inversion effect for chimpanzee than for human faces, while old chimpanzees showed a stronger inversion effect for human than for chimpanzee faces. Hence, we show a relation between the phenomenon face inversion in chimpanzees and the level of specialization to a face category, suggesting a developmental component in second-order configural processing.
CD Dahl, MJ Rasch, M Tomonaga, I Adachi, The face inversion effect in non-human primates revisited – an investigation in chimpanzees (Pan troglodytes). Scientific Reports 3, 2504 (2013). (pdf)