The effect of familiarity and dog's body size on female owners' dog-directed communication.

Exaggerated prosody directed toward dogs has multiple functions, including attention getting and maintaining as well as expressing positive emotions toward the canine partner. However, the role of prosody in owner-dog familiarity remains unclear. To address this gap, we examined the effect of familiarity on the acoustic and visual prosodic features of dog-directed speech. To this end, we analyzed the prosodic features of female speakers when interacting with their own dogs vs. an unfamiliar dog of the same breed during three different situations: Attention-getting, Task-solving, and Nursery rhymes. Interestingly, only the mean pitch was affected by familiarity as speakers used a higher pitch when interacting with the unfamiliar dog compared to their own dog. Meanwhile, pitch range and the intensity of ‘happy’ facial expressions were affected by the dog’s size: speakers used a wider pitch range and more intense ‘happy’ expressions when interacting with smaller dogs. The Nursery rhymes situation evoked the most intense visual prosody, perhaps due to the use of nursery rhymes when interacting with infants. Our results suggest that a heightened overall pitch may serve as a way to appear friendly toward an unfamiliar being, acting as a universal engaging mechanism in human-dog communication. In contrast, the ‘happy’ facial expression and pitch range seem to be less sensitive to the familiarity with a dog, being more influenced by the specific situation and size of the canine partner which is likely related to the ‘cuteness factor’ and/or the baby schema in female speakers.