Can humans recognize emotional state in pet dogs by looking at their face?

Facial expressions are regularly used by humans to detect the emotional state of other people. In 1862 Darwin argued that all species can express emotions and that humans could find out emotions in other animals via both their facial expression and body posture. We investigated whether dogs\u2019 emotional state can be identified by humans by only looking at pictures of a dog\u2019s face and whether experience with dogs can affect this ability. To explore humans\u2019 ability to identify dog\u2019s facial expressions, 27 pictures of dog\u2019s face taken from 9 subjects (different breed, sex, age and colour) under three behaviorally defined conditions (food, alone, reunion) were collected. An on-line questionnaire was developed. Participants were asked to assess the emotional state (positive/negative/don\u2019t know) for every picture. The proportion of correct responses was calculated. Kruskal-Wallis and Mann\u2013Whitney U tests were used to identify differences among categories of people with different experience with dogs (owners, professionals, no experience). The questionnaire was answered by 230 participants (females=159, males=47, NA=24). Participants assigned half of the pictures to the correct emotional state, and positive emotions seemed easier to assess than negative one. \u201cReunion face\u201d was easier to score than \u201cfood face\u201d. Differences were found among categories, and dog owners and professionals recognised the dog\u2019s emotional state significantly better than did people with no experience with dogs. No differences were found between owners and professionals. Our participants were able to identify positive emotional state of dogs, with different morphology, by only looking at their facial expression. In particular, \u201creunion face\u201d seems to be easier to identify compared to \u201cfood face\u201d. This ability seems to be affected by individual everyday experience with dogs. Negative emotional state appears to be more difficult to recognize, possibly because the behavioral situation chosen in the present study (\u201cleft alone\u201d) is not always linked with an intense negative emotional state. Future studies should address the ability of people to assess negative emotional states using pictures of dogs experiencing a more intense emotions (e.g., fear)