Identifying facial expressions associated with positive emotional states in dogs

Positive emotional states have not been studied in animals to any higher extent, but are of great importance in contributing to welfare research. Emotions are to a high degree reflected in facial expressions. The aim of this study was to investigate detailed facial expressions, in order to find indicators of positive emotional states in subtle changes of facial expressions in dogs. This was done by trying to induce dogs to a positive emotional state by presenting two kinds of stimuli presumed to be of positive valence to the dogs, the face of a familiar human talking to the dog in a friendly voice, and a presumed preferred food item consisting of a meatball. Additionally, a wooden block acting as a neutral or slightly negative stimulus was presented, and a small food pellet, assumed to be of neutral valence and used as a baseline stimulus. The dogs were standing in a cubicle and the face of the dogs was recorded five seconds before and five seconds after the different stimuli were revealed. The facial expressions analysed were lip licking, mouth opening and gaze direction. Nine dogs were used in the study and each dog was presented with a sequence of stimuli six times. One-zero sampling was used, with one second intervals. A matched block design was applied, and the test was balanced for the order of stimuli presentations and for morning and afternoon. The results were compared with paired t-tests in three different ways. The lip licking behaviour was assumed to have different meanings depending on how it was performed and which stimulus was presented. The Face stimulus elicited most lip lickings, and investigations showed that the category that was dominant when the Face was presented was the lip lickings not reaching the corner of the mouth. Among these, lip lickings front/up were the most frequent. The lip lickings not reaching the corner of the mouth were probably mostly due to communicative responses, most likely signalling submissive behaviours, but could also indicate displays of positive emotions, or both. The lip lickings observed when the Meatball was presented, on the other hand, could be expected to be a grooming behaviour, consisting of lip lickings reaching the corner of the mouth, due to the sight or smell of food, or the anticipation of it. The Meatball provoked no special changes in facial features, presumably because of the difficulties in detecting non-communicative responses. The mouth opening behaviour had similar results to that of the total lip lickings, and could also be interpreted as a communicative response or an interrupted lip licking. The gaze towards stimuli was difficult to interpret since the different tests were not in accordance with each other, but a tendency towards less gazing at the neutral or slightly negative stimulus was observed in one test. The two assumed positive stimuli did not provoke any general behaviour, which suggests that there is a need to have separate indicators for communicative and non-communicative behaviours. Furthermore, dog behaviours are often ambiguous and should be seen in an environmental context and with other facial expressions and body language included. Further analyses of additional facial expressions, body postures and tail wagging, also recorded during the experiment, will hopefully lead to a higher understanding of the expressions of positive emotions in dogs.