Abstract
Impaired face recognition for certain face categories, such as faces of other species or other age class faces, is known in both humans and non-human primates. A previous study found that it is more difficult for chimpanzees to differentiate infant faces than adult faces. Infant faces of chimpanzees differ from adult faces in shape and colour, but the latter is especially a salient cue for chimpanzees. Therefore, impaired face differentiation of infant faces may be due to a specific colour. In the present study, we investigated which feature of infant faces has a greater effect on face identification difficulty. Adult chimpanzees were tested using a matching-to-sample task with four types of face stimuli whose shape and colour were manipulated as either infant or adult one independently. Chimpanzees' discrimination performance decreased as they matched faces with infant coloration, regardless of the shape. This study is the first to demonstrate the impairment effect of infantile coloration on face recognition in non-human primates, suggesting that the face recognition strategies of humans and chimpanzees overlap as both species show proficient face recognition for certain face colours.
Highlights
Humans extract various sociodemographic information from faces, including gender, ethnicity and age, with high accuracy [1,2]
The present study investigated the impairment effect of infantile coloration on face discrimination in chimpanzees using a well-controlled face morphing technique
The results showed that chimpanzees made more mistakes when matching faces with infant coloration, regardless of the face shape
Summary
Humans extract various sociodemographic information from faces, including gender, ethnicity and age, with high accuracy [1,2]. A number of studies have tested this phenomenon, which is called ‘own-species bias’ [4]. Another example is that humans show better performance in processing faces of their cohort than those of other age classes [5,6,7,8]. Adults can identify the faces of adults better than those of children and vice versa [6]. Similar to this own-age bias, efficient face processing is observed for own-race faces compared with other-race faces [9,10,11]. This superior face processing for certain face types is considered to arise because of the greater exposure of the perceiver to specific face types [4,6,12]
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