Multimodal communication: The integration of visual and acoustic signals by macaques

• Main Author: Partan, Sarah Ruth
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1998
• Subjects: Behavioral psychology; Behaviorial sciences; Psychobiology; Zoology
• ISBN: 9780599079595; 0599079592

Animals often communicate using multiple sensory channels simultaneously. The study of animal communication, however, has traditionally focused on one channel at a time. To gain a more complete understanding of communication, I studied how facial expressions and vocalizations are integrated in an old world primate, the rhesus macaque (Macaca mulatta). I collected data from audio and videotape recordings of social interactions in a population of macaques on Cayo Santiago, Puerto Rico. My first question is: what happens when components from different channels are combined into a composite signal? I classified all possibilities into a comprehensive framework. Components of multimodal signals can have either redundant or nonredundant (unique) meanings. Nonredundant components may interact in any of several ways: each component may carry an independent meaning, or the meaning of one might modulate, modify, or override the other. The second question addressed is: how do rhesus monkeys combine visual and vocal signals? Principal component and multiple correspondence analyses showed consistent associations between certain components of expression. For example, specific mouth positions were tightly paired with particular vocalizations. More surprisingly, specific ear, head, and tail positions were also associated with particular vocalizations. Expressions of threat were more complex and variable than those of fear, as might be expected if threats are spontaneous signals that are assessed by others, while fear is reactive, expressed in direct response to the actions of others. The final question explored is whether monkeys respond to visual and vocal signal components as though they are redundant or unique. I compared responses given to unimodal visual (silent) expressions with those given to bimodal expressions (visual and vocal). Silent threats effectively elicited submissive behavior from recipients. Vocal threats, however, were followed as often by aggressive as by submissive behavior. Affiliative signals that included "girney" vocalizations were followed by grooming sessions more often than were nonvocal signals. Both the threat and affiliative data suggest that vocalizations may add nonredundant information to visual signals. I conclude that multimodal composite signals of rhesus macaques are complex and appear to have both redundant and unique properties, increasing the potential information content of the signal.