Abstract
Humans exhibit a high level of vocal plasticity in speech production, which allows us to acquire both native and foreign languages and dialects, and adapt to local accents in social communication. In comparison, non-human primates exhibit limited vocal plasticity, especially in adulthood, which would limit their ability to adapt to different social and environmental contexts in vocal communication. Here, we quantitatively examined the ability of adult common marmosets (Callithrix jacchus), a highly vocal New World primate species, to modulate their vocal production in social contexts. While recent studies have demonstrated vocal learning in developing marmosets, we know much less about the extent of vocal learning and plasticity in adult marmosets. We found, in the present study, that marmosets were able to adaptively modify the spectrotemporal structure of their vocalizations when they encountered interfering sounds. Our experiments showed that marmosets shifted the spectrum of their vocalizations away from the spectrum of the interfering sounds in order to avoid the overlap. More interestingly, we found that marmosets made predictive and long-lasting spectral shifts in their vocalizations after they had experienced a particular type of interfering sound. These observations provided evidence for directional control of the vocalization spectrum and long-term vocal plasticity by adult marmosets. The findings reported here have important implications for the ability of this New World primate species in voluntarily and adaptively controlling their vocal production in social communication.
Highlights
A hallmark of human vocal communication is voluntary vocal control and vocal learning throughout life [1]
All experimental procedures were approved by the Johns Hopkins University (JHU) Animal Care and Use Committee and in compliance with the guidelines of the National Institutes of Health (NIH)
The common marmoset (Callithrix jacchus) is a highly vocal New World primate with a large vocal repertoire and rich vocal interactions among group members both in the wild and in captivity [41,42]
Summary
A hallmark of human vocal communication is voluntary vocal control and vocal learning throughout life [1]. Humans are able to manipulate many aspects of speech sounds in such situations as learning a foreign language or a local accent These manipulations can be as simple as increasing the amplitude of voice when speaking in a noisy environment (e.g. the Lombard effect) [2] or as complicated as modifying spectrotemporal features of spoken words (e.g. compensatory changes in fundamental frequency [3] or vowel formant [4] when auditory feedback is altered; changes in formant frequency and spectral tilt in response to interfering noise [5,6,7]; modulations in phoneme structures in conversational contexts [8]). Such long-lasting, persistent changes in vocal production (from days to years) [12] is considered long-term vocal plasticity
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