Abstract
The question of whether animals have some sort of self-awareness is a topic of continued debate. A necessary precondition for self-awareness is the ability to visually discriminate the self from others, which has traditionally been investigated through mirror self-recognition experiments. Although great apes generally pass such experiments, interpretations of results have remained controversial. The aim of this study was to investigate how bonobos (Pan paniscus) respond to different types of images of themselves and others, both before and after prolonged mirror exposure. We first presented presumably mirror-naive subjects with representations of themselves in three different ways (mirror image, contingent and non-contingent video footage) as well as representations of others (video footage of known and unknown conspecifics). We found that subjects paid significantly less attention to contingent images of themselves (mirror image, video footage) than to non-contingent images of themselves and unfamiliar individuals, suggesting they perceived the non-contingent self-images as novel. We then provided subjects with three months of access to a large mirror centrally positioned in the enclosure. Following this manipulation, subjects showed significantly reduced interest in the non-contingent self-images, while interest in unknown individuals remained unchanged, suggesting that the mirror experience has led to a fuller understanding of their own self. We discuss implications of this preliminary investigation for the on-going debate on self-awareness in animals.
Highlights
A fundamental question in comparative cognition is whether, or to what degree, nonhuman animals have something akin to self-awareness, that is, whether they can recognise themselves as separate from others and the environment
Prior to the 3-month mirror exposure, we modelled looking time as the response variable, experimental condition as the main predictor variable and subject ID as the random intercept in a linear mixed model (LMM)
The first part of the experiment consisted of exposing subjects to different motion images of themselves, of other group members and of unfamiliar conspecifics
Summary
A fundamental question in comparative cognition is whether, or to what degree, nonhuman animals have something akin to self-awareness, that is, whether they can recognise themselves as separate from others and the environment. Related to this is the question of whether animals, other than humans, have some understanding of their own mental states. It is generally accepted that self-awareness presupposes self-recognition of the body, such as its visual appearance, which is empirically easier to address than mentalistic. Since the 1970s mirrors have been used as the main tool to investigate self-recognition in the visual domain. Evidence for self-recognition is either in the form of spontaneous, self-directed, exploratory behaviours to the mirror image (Swartz, Sarauw & Evans, 1999) or subjects targeting visual markings administered to a body part that is not visible without the aid of a mirror (the ‘‘mirror-mark’’ test; Gallup, 1970)
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