International Journal of Comparative Psychology

Behavioral states and their organization in 5-week old squirrel monkeys and 8-week old capuchin monkeys was evaluated. Infants at these ages are not quite at the threshold, under species-normal rearing conditions, of independent locomotion. Two age-matched infants of each species were observed continuously for a 5-day period while cared for by their mothers in their natal social groups, or while cared for by humans and housed in an incubator on a stationary support. All four infants spent similar proportions of time sleeping, drowsy, nursing, and awake. Hand-rearedinfants were more frequently awake and active with their hands, cocked their heads more often, and slept in shorter bouts than their mother-reared counterparts. All infants exhibited a positive correlation during the daylight hours between the duration of time in an alert quiet state and the duration of time being moved by a carrier. In addition to providing detailed information about the temporal characteristics of state organization and activity within subjects, the findings suggest the kinds of alterations in activity which can result in these species when artificial (largely stationary) rearing regimes are experienced. Many of the alterations can be interpreted as compensatory self-stimulation. The alterations are apparently different in the species studied here from those described for other species, principally macaques, experiencing similar artificial rearing regimes.