Eye contact and vocal responsiveness in squirrel monkey infants and their caregivers

Seventeen newborn squirrel monkeys, housed socially with their mothers and other adult females, were observed during their first 10 days of life. As early as day 1, infants began responding, vocally as well as by eye contact, to vocalizations and gaze directed to them by mothers and allomothers (aunts). Visual contact appeared always to be initiated by the adults. Infants spent less than 4% of awake time in eye contact with adults, but most infant-directed vocalizing occurred during these episodes, when both mothers and allomothers greatly increased their rate of calling. Infants were more likely to respond to vocalizations directed to them while in eye contact; 72% of infants' responsive vocalizing occurred then. These data are compared to those for human mothers and infants, where eye contact has also been shown to stimulate vocal exchange. A functional explanation of the involvement of allomothers, based on the infant's clinging position, is discussed.