It sounds alive! Auditory animacy perception in human adults and domestic chicks

One of the greatest challenges to animal survival is the capacity to distinguish between living and non-living things, an ability defined as animacy perception. Although this phenomenon is well documented in the visual domain, much less is known about the existence of auditory analogues. To address this knowledge gap, we conducted a comparative study aiming at investigating whether those sounds characterised by frequency modulations - like animal voices, a clear living source - are perceived as more animated compared to a monotone sound. The first step in this study was to create a set of synthetic stimuli, one for each modulation observed in animal vocal communication. After that, we conducted two experiments: in the first, we surveyed 65 adult human participants who were asked to rate the perceived animacy of both the synthetic stimuli and domestic chicks’ natural calls, while in the second experiment, using the emotional contagion paradigm, we exposed 2-3-day-old chicks to the same vocalisations and the synthetic stimuli which received the highest and lowest animacy score in the human survey. Our findings suggest that the monotonous stimulus is perceived by humans as less animated compared to modulated stimuli; notably, chicks’ preliminary results also show a similar trend. Frequency modulation, or intonation, is perceived as an auditory animacy cue in human adults.