Small Mirrors Do the Trick: A Simple, but Effective Method to Study Mirror Self-Recognition in Chimpanzees

Kathrin S Kopp,Catherine Crockford,Sonja J Ebel,Roman M Wittig,Daniel B M Haun

doi:10.26451/abc.08.03.05.2021

Abstract

Mirror self-recognition (MSR) is considered an indicator of self-awareness. Standardized mirror tests reveal compelling evidence for MSR in a few non-human species, including all great apes. However, substantial inter-individual variation of MSR within species resulted in an ongoing methodological controversy, questioning the appropriateness of standard MSR tests for cross-species comparisons. Lack of motivation, in particular, is discussed as one possible cause for false negative results. Here, we compare the spontaneous behavioral response of 47 zoo-housed chimpanzees (Pan troglodytes) to (i) standard body-sized, stationary mirrors and (ii) small, portable hand mirrors. We predicted that the monopolizability and maneuverability of small mirrors increase the chances of identifying MSR across a larger proportion of individuals. Chimpanzees both revealed a substantially higher frequency of general mirror-related behaviors and engaged in significantly more and longer behaviors specifically indicating MSR when provided with small mirrors compared to a large mirror. Handheld mirrors provide a more sensitive measure for MSR within and likely between primate species than the traditional large mirrors, and thereby are a potentially valuable tool for studying self-awareness across species.

Highlights

Humans across cultures recognize their specular reflection as their own (Broesch et al, 2011; Kärtner et al, 2012; Keller et al, 2004; Priel & de Schonen, 1986), which is widely considered an indicator of self-awareness (Asendorpf et al, 1996; Bard et al, 2006; Rochat et al, 2012; Suddendorf & Butler, 2013)
We suggest that using small, portable mirrors provides a simple, but promising way to address methodological problems discussed for mirror tests with primates: (i) Individuals can actively reposition handheld mirrors while engaging in SE to maximize visibility of the target body part
Confirming our prediction, chimpanzees spent more time interacting with small mirrors than with the large mirror, with interaction times varying considerably across individuals (Table 1, Figure 1A)

Summary

Introduction

Humans across cultures recognize their specular reflection as their own (mirror self-recognition, MSR) (Broesch et al, 2011; Kärtner et al, 2012; Keller et al, 2004; Priel & de Schonen, 1986), which is widely considered an indicator of self-awareness (Asendorpf et al, 1996; Bard et al, 2006; Rochat et al, 2012; Suddendorf & Butler, 2013). While MSR is a universal human trait, intriguingly, in most studies, less than half of great apes demonstrated compelling evidence for MSR This raised an ongoing controversy concerning methodological issues of MSR tests possibly generating false negatives Several studies in different species considered direct physical access to the mirror as an important factor stimulating MRB because it allowed tactile examination and looking behind the mirror (Anderson, 1984; Gallup Jr., 1994; Reiss & Morrison, 2017). Köhler did not describe frequencies of MRB or compare the chimpanzees’ interactions with small mirrors to those with large mirrors

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