Body condition-linked alterations in dog owners' visual prosody

Introduction Visual prosody, the facial component accompanying speech, plays an important role in human social communication and is also a characteristic feature of dog-directed communication. Previous studies have shown that dog-directed visual prosody shares several features with infant-directed communication, although it also exhibits characteristics that differ between dogs and infants. Obesity has been associated with altered emotional processing and expression in humans, yet its potential effects on visual prosody have not been investigated. In the present study, we examined whether obesity is associated with variation in visual prosody during dog-directed communication. Methods We analysed video recordings of 146 adult speakers interacting with their own dogs, infants, or adult human partners in semi-naturalistic settings, meaning that they were given instructions what to do, but these instructions were aimed to mimic real-life situations. Facial movements were quantified using automated facial coding software (Noldus FaceReader), and body shape was visually scored based on standard procedure. Linear mixed models were used to analyse Happy facial expression, facial Arousal, Valence, and activation of the cheek raiser muscle (AU6). Results Body condition-related differences depended on both the communication partner and the facial variable examined. Lower facial arousal was detected in speakers with higher body condition scores across all communication contexts. In contrast, differences in positive facial expressions were specific to dog-directed communication: speakers with higher body condition scores displayed less intense Happy facial expressions and lower facial Valence when interacting with dogs, whereas no such differences were observed in infant- or adult-directed communication. Unexpectedly, higher body condition scores were associated with stronger cheek raiser (AU6) intensity during infant- and adult-directed communication, but not during dog-directed communication, which might be a species-specific compensation mechanism. In addition, replicating previous findings, female speakers displayed more intense positive facial expressions and facial arousal than males, although these gender differences were reduced in dog-directed interactions. Discussion Our findings suggest that body condition is associated with variation in visual prosody, but these effects depend on the interlocutor and particularly pronounced during dog-directed communication. Different interpretations of these findings are presented in the discussion: altered mapping of muscle movement to FaceReader output, differences in FaceReader model quality, differences in habitual communicative style or expressivity, the amplifying or masking effect of communication differences, and a possible compensatory mechanism. The importance of these body condition-related alterations on the effectiveness of face-to-face communication, as well as social relationships need to be discussed.