Efficient search for a face by chimpanzees (Pan troglodytes).

Masaki Tomonaga,Tomoko Imura

doi:10.1038/srep11437

Abstract

The face is quite an important stimulus category for human and nonhuman primates in their social lives. Recent advances in comparative-cognitive research clearly indicate that chimpanzees and humans process faces in a special manner; that is, using holistic or configural processing. Both species exhibit the face-inversion effect in which the inverted presentation of a face deteriorates their perception and recognition. Furthermore, recent studies have shown that humans detect human faces among non-facial objects rapidly. We report that chimpanzees detected chimpanzee faces among non-facial objects quite efficiently. This efficient search was not limited to own-species faces. They also found human adult and baby faces-but not monkey faces-efficiently. Additional testing showed that a front-view face was more readily detected than a profile, suggesting the important role of eye-to-eye contact. Chimpanzees also detected a photograph of a banana as efficiently as a face, but a further examination clearly indicated that the banana was detected mainly due to a low-level feature (i.e., color). Efficient face detection was hampered by an inverted presentation, suggesting that configural processing of faces is a critical element of efficient face detection in both species. This conclusion was supported by a simple simulation experiment using the saliency model.

Highlights

The face is quite an important stimulus category for human and nonhuman primates in their social lives
We report that chimpanzees detected chimpanzee faces among non-facial objects quite efficiently
Efficient face detection was hampered by an inverted presentation, suggesting that configural processing of faces is a critical element of efficient face detection in both species

Summary

Introduction

The face is quite an important stimulus category for human and nonhuman primates in their social lives. When a first-order spatial configuration among facial features (horizontally arranged eyes and nose and mouth located beneath the eyes) is distorted, face recognition is readily disturbed[3] This result strongly suggests that humans process faces in a holistic manner. Hershler and Hochstein clearly demonstrated this phenomenon using various stimuli and experimental conditions[12] They suggested that the pop-out effect or very efficient searching is caused by low-level “features”, as Treisman et al initially proposed[9], and by higher-order object categories such as faces[12,13], controversies remain[14,15]. Chimpanzees exhibit results similar to humans regarding spatial attention caused by facial stimuli[8] These findings suggest that chimpanzees rapidly detect a face among non-face objects, as determined in humans by Hershler and Hochstein[12]

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Results

Conclusion