Abstract
Vocal expressions of emotions follow simple rules to encode the inner state of the caller into acoustic parameters, not just within species, but also in cross-species communication. Humans use these structural rules to attribute emotions to dog vocalizations, especially to barks, which match with their contexts. In contrast, humans were found to be unable to differentiate between playful and threatening growls, probably because single growls' aggression level was assessed based on acoustic size cues. To resolve this contradiction, we played back natural growl bouts from three social contexts (food guarding, threatening and playing) to humans, who had to rate the emotional load and guess the context of the playbacks. Listeners attributed emotions to growls according to their social contexts. Within threatening and playful contexts, bouts with shorter, slower pulsing growls and showing smaller apparent body size were rated to be less aggressive and fearful, but more playful and happy. Participants associated the correct contexts with the growls above chance. Moreover, women and participants experienced with dogs scored higher in this task. Our results indicate that dogs may communicate honestly their size and inner state in a serious contest situation, while manipulatively in more uncertain defensive and playful contexts.
Highlights
During social interactions, both humans and non-human animals use various communicative signals to express their inner states
Each growl sample was used in five sets, and within one set the growls from the same context originated from different dogs
Each playback set was used for two listeners only, each individual growl sample was evaluated by 10 participants
Summary
Both humans and non-human animals use various communicative signals to express their inner states. The way in which emotions are reflected in the acoustic structure of calls is best described by the Source-Filter Framework (for detailed review see [1]). The specific changes in the brain due to emotional states can affect the neural control over the muscle movements involved in voice production in the larynx and the vocal tract, and these changes modify certain acoustic parameters of the produced calls [2].
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