Relevance of facial expression and posture as cues in communication of affect between monkeys.

Some form of nonverbal communication is involved to a variable degree in every human interaction. Even verbal communication involves more than just the words that are used; intonation, speed of speech, gestures, and a variety of other factors modify the meaning of the words. 20,21 Further, every “intuitive” percept and every “empathic” relationship are dependent upon some nonverbal communication of affects. Although the precise nature of this form of communication is still obscure, it undoubtedly plays a significant role in the social relations among men, 22,23 among animals, 12,21 and between man and animal. 6,14 In order to delineate the factors involved in the communication of affects, a method was devised for the experimental study of such communication among monkeys. 15 Thus, a monkey was conditioned to press a bar (conditioned avoidance response) at the sight of another monkey (conditioned stimulus) which served as a signal