Delayed imitation of lipsmacking gestures by infant rhesus macaques (Macaca mulatta).

Annika Paukner,Stephen J Suomi,Pier F Ferrari,Angela Sirigu

doi:10.1371/journal.pone.0028848

Abstract

Human infants are capable of accurately matching facial gestures of an experimenter within a few hours after birth, a phenomenon called neonatal imitation. Recent studies have suggested that rather than being a simple reflexive-like behavior, infants exert active control over imitative responses and ‘provoke’ previously imitated gestures even after a delay of up to 24 h. Delayed imitation is regarded as the hallmark of a sophisticated capacity to control and flexibly engage in affective communication and has been described as an indicator of innate protoconversational readiness. However, we are not the only primates to exhibit neonatal imitation, and delayed imitation abilities may not be uniquely human. Here we report that 1-week-old infant rhesus macaques (Macaca mulatta) who show immediate imitation of a lipsmacking gesture also show delayed imitation of lipsmacking, facilitated by a tendency to refrain from lipsmacking toward a still face during baseline measurements. Individual differences in delayed imitation suggest that differentially matured cortical mechanisms may be involved, allowing some newborns macaques to actively participate in communicative exchanges from birth. Macaque infants are endowed with basic social competencies of intersubjective communication that indicate cognitive and emotional commonality between humans and macaques, which may have evolved to nurture an affective mother-infant relationship in primates.

Highlights

Neonatal imitation, the phenomenon that newborn human infants can accurately match facial gestures, was reported over 30 years ago [1], and remains a thriving research topic within the social sciences
We suggest that increases in the frequency of LPS gestures after seeing a human experimenter demonstrate LPS gestures compared to a still face baseline, the increase being larger in the lipsmacking condition than in other control conditions, can be seen as evidence of neonatal imitation
We presented three different stimuli to infants: a lipsmacking gesture (LPS, rapid opening and closing of the mouth), a tongue protrusion gesture as a facial motion control condition (TP, protrusion and retraction of the tongue), and a non-biological control condition (CTRL; a white plastic disk with orthogonal black and red stripes was slowly rotated left and right; see Figure 1A)

Summary

Introduction

The phenomenon that newborn human infants can accurately match facial gestures, was reported over 30 years ago [1], and remains a thriving research topic within the social sciences. Laboratory assessments generally infer imitation when the frequency of a target behavior after modeling is greater than the frequency of the same behavior in a control condition. This conceptualization is purely based on behavior, and does not address issues such as intentionality, uniqueness, novelty, or generalizability of the imitated gesture. As Heimann, page 74, [15] writes, ‘‘Viewed in this way, there is no doubt that neonatal imitation is a real phenomenon. It does exist and it can be demonstrated as has been shown by numerous research groups’’

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