Sound on the rebound: Bringing form and function back to the forefront in understanding nonhuman primate vocal signaling

Abstract

In this review, we will examine some difficulties engendered by a linguistically inspired, meaning-based view of primate calls, specifically that vocalizations are arbitrarily structured vehicles for transmitting encoded referential information. The fundamental problem is that this characterization, while metaphorical, is often taken literally. While researchers have thus usefully been spurred to demonstrate that primates sometimes do behave as if their vocalizations are referential, this "metaphor-as-explanation" approach has also distracted them from normative biological perspectives and the structure-function relationships that likely exist in the signals. After a brief historical introduction, we consider some of the problems raised by relying on linguistically based constructs, and suggest two ways in which acoustic structure may be tied to simple, nonlinguistic functions in primate vocalizations. We then consider the evolution of these calling strategies in light of the sometimes coincident, but other times divergent interests of senders and receivers. A BIT OF HISTORY The Classical-Ethology ApproachContemporary acoustic primatology ultimately derives from traditional ethological theory, which viewed signals as "sign stimuli" serving to "release" behavior in conspecifics. Many of the signals studied were visual displays, which, in their original form, were thought to be connected to a particular function. In birds, for example, preparatory movements preceding flight were suggested as the origin of signals of imminent take-off, while head-bowing associated with physical attack was proposed to have given rise to aggressive gestures. Although emancipation from these first forms was also considered an important part of signal evolution, this approach implied that structure would always provide telltale clues to the origins of displays.Seminal work on vocal signaling later emphasized form and function even more strongly, as illustrated by Marler's 1 studies of small birds, in which alerting calls trigger either hiding or active mobbing. Marler found that in many species cryptic behavior occurs in response to a ventriloquial, high-pitched "seet" call, while a harsh, broadband, and easily localizable "chirp" is used to elicit mobbing. He later documented a parallel phenomenon in forest primates, suggesting that the relationship might be widespread. 2 This work also set the stage for examining the influence Michael J. Owren is Assistant Professor in the Department of Psychology at Cornell University in Ithaca, NY. His work has examined primate audition and perceptual processing of species-typical sounds, vocal development, and acoustic analysis of vocalizations in vervets, macaques, baboons, and proboscis monkeys. His current interests include the role of nonlinear dynamics in primate calls and nonlinguistic aspects of human vocal behavior. Drew Rendall is Assistant Professor in the Department of Psychology and Neuroscience at the University of Lethbridge in Lethbridge, Alberta. His interests are in the intersectio...

Context-related call combinations in female Diana monkeys

“…In Diana monkeys, the concatenation of one of several possible introductory calls to the arched call unit seems to function as a contextual refiner of this contextually neutral call. The degree to which these subtleties are intentionally produced, mere reflections of a caller's motivational state (Owings and Morton 1998;Owren and Rendall 2001) or both has not been addressed by this study and will require further investigation.…”

Barking in domestic dogs: context specificity and individual identification

“…The differences we found are also consistent with the idea that particular sounds routinely affect listeners by altering their attention and/or arousal. Harsh, highamplitude sounds increase arousal (Owren & Rendall 2001) and rapidly repeated sounds correlate with increased motor activity and may even elicit higher arousal in the receiver (McConnell & Baylis 1985;McConnell 1990). One mechanism for this increased arousal is that the repeated vocalizations may achieve a cumulative or tonic effect by improving the signal-to-noise ratio and consequently achieve a critical threshold that maintains a behavioural state in the perceiver (Schleidt 1973).…”

Predator-deterring alarm call sequences in Guereza colobus monkeys are meaningful to conspecifics

“…Morton 1977;Owren & Rendall 2001). Yet, a number of studies have challenged this stance by showing that alarm calling in primates and other animal species can be the product of more complicated cognitive pro-cessing, sometimes as part of specific biological functions such as conspecific warning or predator deterrence (e.g.…”

“…An alternative explanation is that such findings are the result of receiver biases, caused by the mere acoustic characteristics of a signal, not by any mental representations or memories associated with them (e.g. Morton 1977;Fichtel et al 2001;Owren & Rendall 2001;Rendall 2003). An extreme version of this position is that receivers are mere automatons whose responses can be triggered by specific physical stimuli.…”