A study examines how states of arousal and social context influence vocalization in marmoset monkeys. Unraveling how nonhuman primates produce and use vocalizations could lend insight into the evolution of human communication. However, whether nonhuman primate vocalizations are volitional, similar to human speech, or bound to internal states, such as arousal, remains unclear. Asif A. Ghazanfar and colleagues examined the relationship between arousal and vocalization in pair-bonded marmoset monkeys ( Callithrix jacchus ) in a variety of contexts in which physical distance was manipulated to excite different levels of arousal in the monkeys. The authors measured acoustic changes and used noninvasive electromyography to measure heart rate fluctuations--a measure of arousal--in the monkeys, and found that monkey vocalization changed systematically with different distances between the monkeys. However, vocalization changes were also influenced by external factors, such as the timing of another monkey's vocalizations. The latter finding is contrary to the suggestion that changes in vocal production in monkeys are linked to arousal levels. According to the authors, the study suggests that, similar to human speech, both internal and external factors influence nonhuman primate vocal production.
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Article #17-22426: "Internal states and extrinsic factors both determine monkey vocal production," by Diana Liao, Yisi Zhang, Lili Cai, and Asif A Ghazanfar.
MEDIA CONTACT: Asif A. Ghazanfar, Princeton University, NJ; tel: 609-258-9314; e-mail: asifg@princeton.edu
Proceedings of the National Academy of Sciences