Pitch affects human (Homo sapiens) perception of emotional arousal from diverse animal calls.

A growing body of research demonstrates that humans can accurately perceive the emotional states of animals solely by listening to their calls, highlighting shared evolutionary ancestry. Yet, the cognitive and perceptual mechanisms underlying heterospecific emotion perception have remained open to investigation. One hypothesis is that humans rely on simple acoustic heuristics to make such judgments, for example, perceiving higher-pitched calls as reflecting heightened emotional arousal (the "pitch rule"). This could lead to accurate judgments of emotion since in most mammals, as in humans, vocal fundamental frequency (the acoustic determinant of the pitch percept) does objectively correlate with emotional arousal. In the present study, we used digital pitch manipulation to create pairs of animal calls that were perceptually identical except for pitch, and we measured human perceptions of the caller's emotional arousal using an online survey. Calls of six phylogenetically diverse species were included as stimuli. Participants attributed slightly but statistically significantly higher arousal to higher-pitched versions of the same calls. Variation in application of the pitch rule across species was not well explained by familiarity, and prior experience with cats did not significantly predict sensitivity to pitch in cat vocalizations. Cross-species variation also did not align with phylogenetic distance from humans, or the hypothetical usefulness of pitch for making accurate judgments. Thus, the pitch rule may be a "mammalomorphic" heuristic leading to accurate emotion judgments in some taxa and call types and erroneous judgments in others, depending in part on phylogenetic distance and the mechanisms of call production. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Loosening the leash: The unique emotional canvas of human screams.

We use screams to explore ideas presented in the target article. Evolving first in animals as a response to predation, screams reveal more complex social use in nonhuman primates and, in humans, uniquely, are associated with a much greater variety of emotional contexts including fear, anger, surprise, and happiness. This expansion, and the potential for manipulation, promotes listener social vigilance.

Humans read emotional arousal in monkey vocalizations: evidence for evolutionary continuities in communication.

Humans and other mammalian species communicate emotions in ways that reflect evolutionary conservation and continuity, an observation first made by Darwin. One approach to testing this hypothesis has been to assess the capacity to perceive the emotional content of the vocalizations of other species. Using a binary forced choice task, we tested perception of the emotional intensity represented in coos and screams of infant and juvenile female rhesus macaques (Macaca mulatta) by 113 human listeners without, and 12 listeners with, experience (as researchers or care technicians) with this species. Each stimulus pair contained one high- and one low-arousal vocalization, as measured at the time of recording by stress hormone levels for coos and the degree of intensity of aggression for screams. For coos as well as screams, both inexperienced and experienced participants accurately identified the high-arousal vocalization at significantly above-chance rates. Experience was associated with significantly greater accuracy with scream stimuli but not coo stimuli, and with a tendency to indicate screams as reflecting greater emotional intensity than coos. Neither measures of empathy, human emotion recognition, nor attitudes toward animal welfare showed any relationship with responses. Participants were sensitive to the fundamental frequency, noisiness, and duration of vocalizations; some of these tendencies likely facilitated accurate perceptions, perhaps due to evolutionary homologies in the physiology of arousal and vocal production between humans and macaques. Overall, our findings support a view of evolutionary continuity in emotional vocal communication. We discuss hypotheses about how distinctive dimensions of human nonverbal communication, like the expansion of scream usage across a range of contexts, might influence perceptions of other species' vocalizations.

Vocal expression of emotional arousal across two call types in young rhesus macaques.

As Darwin first recognized, the study of emotional communication has the potential to improve scientific understanding of the mechanisms of signal production as well as how signals evolve. We examined the relationships between emotional arousal and selected acoustic characteristics of coo and scream vocalizations produced by female rhesus macaques, Macaca mulatta, during development. For coos, arousal was assessed through measures of stress-induced elevations of plasma cortisol exhibited in response to the human intruder test. In the analysis of screams, arousal was evaluated from the intensity of aggression experienced by the vocalizer during natural social interactions. Both call types showed a positive relationship between arousal and overall fundamental frequency (F0, perceived as pitch in humans). In coos, this association was dampened over development from infancy (6 months) to the juvenile, prepubertal period (16 months) and further to menarche (21.3-31.3 months), perhaps reflecting developmental changes in physiology, anatomy and/or call function. Heightened arousal was also associated in coos with increases in an acoustic dimension related to F0 modulation and noisiness. As monkeys matured, coos showed decreases in overall F0 as well as increased noisiness and F0 modulation, likely reflecting growth of the vocal apparatus and changes in vocal fold oscillation. Within screams, only one acoustic dimension (related to F0 modulation) showed developmental change, and only within one subclass of screams within one behavioural context. Our results regarding the acoustic correlates of arousal in both call types are broadly consistent with findings in other species, supporting the hypothesis of evolutionary continuity in emotion expression. We discuss implications for broader theories of how vocal acoustics respond to selection pressures.

The emotional canvas of human screams: patterns and acoustic cues in the perceptual categorization of a basic call type.

Screams occur across taxonomically widespread species, typically in antipredator situations, and are strikingly similar acoustically, but in nonhuman primates, they have taken on acoustically varied forms in association with more contextually complex functions related to agonistic recruitment. Humans scream in an even broader range of contexts, but the extent to which acoustic variation allows listeners to perceive different emotional meanings remains unknown. We investigated how listeners responded to 30 contextually diverse human screams on six different emotion prompts as well as how selected acoustic cues predicted these responses. We found that acoustic variation in screams was associated with the perception of different emotions from these calls. Emotion ratings generally fell along two dimensions: one contrasting perceived anger, frustration, and pain with surprise and happiness, roughly associated with call duration and roughness, and one related to perceived fear, associated with call fundamental frequency. Listeners were more likely to rate screams highly in emotion prompts matching the source context, suggesting that some screams conveyed information about emotional context, but it is noteworthy that the analysis of screams from happiness contexts (n = 11 screams) revealed that they more often yielded higher ratings of fear. We discuss the implications of these findings for the role and evolution of nonlinguistic vocalizations in human communication, including consideration of how the expanded diversity in calls such as human screams might represent a derived function of language.

Do human screams permit individual recognition?

The recognition of individuals through vocalizations is a highly adaptive ability in the social behavior of many species, including humans. However, the extent to which nonlinguistic vocalizations such as screams permit individual recognition in humans remains unclear. Using a same-different vocalizer discrimination task, we investigated participants' ability to correctly identify whether pairs of screams were produced by the same person or two different people, a critical prerequisite to individual recognition. Despite prior theory-based contentions that screams are not acoustically well-suited to conveying identity cues, listeners discriminated individuals at above-chance levels by their screams, including both acoustically modified and unmodified exemplars. We found that vocalizer gender explained some variation in participants' discrimination abilities and response times, but participant attributes (gender, experience, empathy) did not. Our findings are consistent with abundant evidence from nonhuman primates, suggesting that both human and nonhuman screams convey cues to caller identity, thus supporting the thesis of evolutionary continuity in at least some aspects of scream function across primate species.