Development of vocal recognition of mothers in infant Japanese macaques.

Individual vocal recognition was studied in infant Japanese macaques by presenting natural calls of mothers and nonmother cagemates to them in a habituation-dishabituation paradigm. Discriminability was measured by an increase in conditioned sucking response rate to a second stimulus call after habituation to the first stimulus call. Recovery from habituation was greater in subjects over 190 days postconception when mother's vocalizations were played back after the stimulus change than when sounds of others were presented. Results demonstrate that the subjects could sort acoustic variants of vocalizations given by their cagemates into at least two categories (mother versus others) and suggest that vocal recognition of mothers develops relative to postconception (maturational) rather than postnatal age in Japanese macaques.