Internal states and extrinsic factors both determine monkey vocal production

Abstract

A key question for understanding speech evolution is whether or not the vocalizations of our closest living relatives-nonhuman primates-represent the precursors to speech. Some believe that primate vocalizations are not volitional but are instead inextricably linked to internal states like arousal and thus bear little resemblance to human speech. Others disagree and believe that since many primates can use their vocalizations strategically, this demonstrates a degree of voluntary vocal control. In the current study, we present a behavioral paradigm that reliably elicits different types of affiliative vocalizations from marmoset monkeys while measuring their heart rate fluctuations using noninvasive electromyography. By modulating both the physical distance between marmosets and the sensory information available to them, we find that arousal levels are linked, but not inextricably, to vocal production. Different arousal levels are, generally, associated with changes in vocal acoustics and the drive to produce different call types. However, in contexts where marmosets are interacting, the production of these different call types is also affected by extrinsic factors such as the timing of a conspecific's vocalization. These findings suggest that variability in vocal output as a function of context might reflect trade-offs between the drive to perpetuate vocal contact and conserving energy.

Vocal learning: Beyond the continuum

“…Turning first to primates, both monkeys and apes display relevant behavior. Marmosets, a New World monkey who engages in turn taking [62], uses different proportions of affiliative call types depending on social distance [63], as well as loudness relative to physical distance [64]. They can also convey identity through aspects of their calls [65].…”

Compensatory mechanisms affect sensorimotor integration during ongoing vocal-motor acts in marmoset monkeys

“…Vocal flexibility during perturbing noise in marmoset monkeys. Current studies have control when [14], where [38], and what to vocalize [39]. In addition, recent studies revealed 232 that marmosets are able to modulate distinct call parameters in response to acoustic 233 feedback [18,40].…”

Emotion Communication Through Voice Modulation: Insights on Biological and Evolutionary Underpinnings of Language

“…Hence, it is plausible that the ability to associate emotional content to specific changes in the voice, which goes beyond the association between discrete units and their denotation, constitutes a fundamental evolutionary precursor of language. Future research shall further address this line of investigation, which will advance the study of the evolutionary vocal precursors of language, placing it into a fruitful perspective (see Liao, Zhang, Cai, & Ghazanfar, 2018).…”

“…Recent research on marmoset monkeys (Callithrix jacchus) investigated whether monkey calls are automatic reflexes intrinsically linked to internal states such as emotional arousal, or whether they result from a degree of volitional vocal control, and can thus be strategically used to manipulate the listeners' reactions (Liao et al, 2018). Interestingly, the authors found that physical distance from a conspecific and visual access to her/him affected the level of arousal, resulting into different vocal behaviors.…”