Do Great Apes Know Each Other's Names? Probing Great Ape Comprehension of Social Vocal Labels

Humans use proper names as vocal labels to identify and communicate with and about social agents. The comprehension of spoken proper names requires the ability to interpret socially specific verbal signals, or social vocal labels, and use cross-modal perception to identify and discriminate between group members. Individuals that recognize and comprehend familiar proper names can use these labels to identify and discriminate between groupmates, gain third-party knowledge, and guide decision-making. Use of vocal labels for conspecifics is noticeably rare in the animal kingdom, and has only been found in species (dolphins, elephants, and marmosets) that are phylogenetically distant from humans. We therefore investigated the phylogenetic trajectory of this capacity by studying our closest living primate relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). We implemented a cross-modal non-invasive eye-tracking and playback study with multiple populations of apes (N = 24) living in zoos and sanctuaries, none of whom were specifically language-trained. We tested whether chimpanzees and bonobos spontaneously attend toward an image of a groupmate whose name has been called by a human caretaker. We found limited evidence that apes link the caretaker-given names of their groupmates to images on a screen, and therefore cannot make strong conclusions about apes’ comprehension of these social vocal labels. Our playback and eye-tracking paradigm offers a novel tool for studying cross-modal perception and knowledge of vocal labels. Future work will be critical to identify the sociocognitive foundations underlying socially specific referential communication and the evolution of language.