Humans recognize affective cues in primate vocalizations: Acoustic and phylogenetic perspectives

Abstract

Humans are adept in extracting affective information from the vocalisations of not only humans but also other animals. Current research has mainly focused on phylogenetic proximity to explain such cross-species emotion recognition abilities. However, because research protocols are inconsistent across studies, it remains unclear whether human recognition of vocal affective cues of other species is due to cross-taxa similarities between acoustic parameters, the phylogenetic distances between species, or a combination of both. To address this, we first analysed acoustic variation in 96 affective vocalizations, including agonistic and affiliative contexts, of humans and three other primate species : rhesus macaques, chimpanzees and bonobos; the latter two being equally phylogenetically distant from humans. Using Mahalanobis distances, we found that chimpanzee vocalizations were acoustically closer to those of humans than to those of bonobos, confirming a potential derived vocal evolution in the bonobo lineage. Second, we investigated whether human participants recognized the affective basis of vocalisations through tasks by asking them to categorize (A vs B) or discriminate (A vs non-A) vocalisations based on their affective content. Results showed that participants could reliably categorize and discriminate most of the affective vocal cues expressed by other primates, except threat calls by bonobos and macaques. Overall, participants showed greatest accuracy in detecting chimpanzee vocalizations; but not bonobo vocalizations, which provides support for both the phylogenetic proximity and acoustic similarity hypotheses. Our results highlight for the first time the importance of both phylogenetic and acoustic parameter level explanations in cross-species affective perception, drawing a more complex picture to explain our natural understanding of animal signals.

Towards a great ape dictionary: Inexperienced humans understand common nonhuman ape gestures

“…Where gestures had alternate meanings, these were also detected more often than chance in two gesture types. That our participants were able to interpret primate signals complements recent findings that suggest humans may be able to perceive affective cues in primate vocalisations [44].…”

Frontal mechanisms underlying primate calls recognition by humans

“…This was especially surprising considering that previous studies have mostly found a better recognition rate for chimpanzee vocalizations compared to the calls of other non-human primates (46,51). Hence, our behavioral analysis suggests that the capacity of modern humans to accurately identify non-human primate calls could rely more heavily on acoustic similarity rather than phylogenetic proximity alone (52).…”

“…Therefore, OFC and IFG brain areas-especially IFGtri activity-may be the necessary biological and functional 'hardware' allowing Homo sapiens to classify and integrate nonverbal communication, be it human voice or other primate vocalizations. Such ability may then have been co-opted for the treatment of the proto-language used by our human ancestors, although precisely how close this proto-language was from to today's non-human primates vocalizations remains an open question , with a question mark regarding a potential interaction with between-species acoustical differences (52). We contend that the common activity we evidenced in the OFC and IFG across stimuli suggests that such proto-language may have shared acoustic properties with non-human primate vocalizations.…”

Threat Vocalisations are Acoustically Similar between Humans (Homo sapiens) and Chimpanzees (Pan troglodytes)

“…Moreover, human perception is limited by the sensitivity of the human ear and perception studies may therefore not fully capture the similarities in acoustic structures. For instance, in a recent study, acoustic similarities between primate vocalisations did not predict human listeners' perceptual judgments (Debracque et al, 2022). In order to assess evolutionary continuity in vocalisations, we thus need to directly compare acoustic structures of vocalisations mapping onto specific types of behavioural contexts across humans and other species.…”