Still Face in Pet Dogs (Canis familiaris)

Dogs are able to cooperate in reciprocal exchange with humans but little is known about the extent of these abilities (Range & Viranyi, 2015). In the Still Face paradigm, infants reply to a sudden nonreciprocal facial expression with gaze aversion and an increase in re-engagement and distress behaviors (E. Tronick et al., 1978). We directly adapted this method; the dog's owner talked to the dog, then abruptly switched to a still, neutral face, maintaining eye contact. In Study 1 (N = 20), we found that dogs showed a significant decrease in the amount of looking at the owner in the Still Face phase, paralleling the results found in gaze aversion in infants, and they performed fewer pawing and vocalizations toward the person in the Still Face phase. In Study 2 (N = 60), we included one condition of continuous physical contact, and one condition that was a direct replication of the initial study without physical contact. Similar to human infants, we found a significant decrease in looking from the Interaction phase to the Still Face phase. However, in contrast to human infants, re-engagement and stress behaviors were higher in the Interaction phase than the Still Face phase. Looking and re-engagement behaviors differed based on the condition, with a smaller difference between phases in the Petting condition. These results suggest that dogs are capable of perceiving these small changes in human affect. However, unlike human infants, dogs seem to have greater expectations about physical interactions than verbal interactions, as they reacted more strongly to an Interaction phase without physical contact than the Still Face.