Effects of age, objects, and visual experience on affective responses of rhesus monkeys to strangers.

Studied the development of lipsmacking and grimacing, facial expressions associated with friendliness and fear, respectively, in 26 rhesus monkeys raised under 3 conditions that included visual exposure to (a) monkeys and people, (b) one monkey, (c) neither monkeys nor people. Ss were tested through Life Weeks 1–22 for responses to their mirror image or a human face. Age, stimulus configuration, and experience interacted in the development of the 2 responses. Lipsmacking generally occurred earlier than grimacing and was most frequently elicited by the face. Frequency of lipsmacking increased initially, then declined; in contrast, frequency of grimacing increased progressively throughout testing. Rearing conditions significantly affected age of first response, level of responsiveness, and stimulus differentiation. The most restricted group was oldest at first response, least responsive, and showed the weakest differentiation of stimuli; the most experienced group was at the opposite extreme on these comparisons. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)