The origins of trust: Humans' reliance on communicative cues supersedes firsthand experience during the second year of life

How do people learn about things that they have never perceived or inferred-like molecules, miracles or Marie-Antoinette? For many thinkers, trust is the answer. Humans rely on communicated information, sometimes even when it contradicts blatantly their firsthand experience. We investigate the early ontogeny of this trust using a non-verbal search paradigm in four main studies and three supplementary studies (N = 208). Infants and toddlers first see where a reward is, and then an informant communicates to them that it is in another location. We use this general experimental set-up to assess the role of age, informants' knowledge, cue's familiarity, and communicative context on trust in communicated information. Results reveal that infants and toddlers quickly trust familiar and novel communicative cues from well-informed adults. When searching for the reward, they follow a well-informed adults' communicative cue, even when it contradicts what they just saw. Furthermore, infants are less likely to be guided by familiar and novel cues from poorly informed adults than toddlers. Thus, reliance on communication is calibrated during early childhood, up to the point of overriding evidence about informants' knowledge. Moreover, toddlers trust much more strongly a novel cue when it is used in a communicative manner. Toddlers' trust cannot be explained by mere compliance: it is highly reduced when communicated information is pitted against what participants currently see. Thus, humans' strong tendency to rely on familiar and novel communicative cues emerges in infancy, and intensifies during the second year of life.