Early experience affects the strength of vigilance for threat in rhesus monkey infants.

Both human and nonhuman primates exhibit a cognitive bias to social threat, but little is known about how this bias develops. We investigated the development of threat bias in free-ranging infant rhesus macaques (Macaca mulatta) at 3 months (n = 45) and 9 months (n = 46) of age. Three-month-olds did not display bias, but 9-month-olds exhibited increased maintenance of attention to threatening social stimuli. To examine whether the social environment affected this increased vigilance for threat, we collected behavioral data on maternal rank and protectiveness across the first 12 weeks of life for infants tested at 9 months. Among 9-month-olds, those of high-ranking and more protective mothers displayed greater vigilance for threat than those of lower-ranking and less protective mothers. These results demonstrate that infant social cognition is shaped by mothers both directly (via protectiveness) and indirectly (through social rank).