Abstract
Facial expressions are considered sensitive indicators of emotional states in humans and many animals. Identifying facial indicators of emotion is a major challenge and little systematic research has been done in non-primate species. In dogs, such research is important not only to address fundamental and applied scientific questions but also for practical reasons, since many problem behaviours are assumed to have an emotional basis, e.g. aggression based on frustration. Frustration responses can occur in superficially similar contexts as the emotional state of positive anticipation. For instance, the anticipated delivery of a food reward may induce the state of positive anticipation, but over time, if the food is not delivered, this will be replaced by frustration. We examined dogs’ facial expressions in contexts presumed to induce both positive anticipation and frustration, respectively, within a single controlled experimental setting. Using DogFACS, an anatomically-based method for coding facial expressions of dogs, we found that the “Ears adductor” action was more common in the positive condition and “Blink”, “Lips part”, “Jaw drop”, “Nose lick”, and “Ears flattener” were more common in the negative condition. This study demonstrates how differences in facial expression in emotionally ambiguous contexts may be used to help infer emotional states of different valence.
Highlights
Facial expressions are considered sensitive indicators of emotional states in humans and many animals
“Ears adductor” (EAD102) was the only variable that was more common in the positive condition while “Blink” (Action Unit 145 = AU145), “Lips part” (AU25), “Jaw drop” (AU26), “Nose lick” (AD137), and “Ears flattener” (EAD103) were more common in the negative condition
Using a within-subject design, this study explored facial expressions of dogs in two superficially similar conditions involving a food reward: (1.) positive: expectation of access to a high-value food reward, and (2.) negative: denial of access to the food reward
Summary
Facial expressions are considered sensitive indicators of emotional states in humans and many animals. Emotions can be classified either within a multidimensional space, often along two axes comprising arousal (i.e. high versus low) and hedonic valence (i.e. positivity versus negativity of an emotion; e.g.3), or as discrete states (e.g. happiness, fear, frustration; e.g.4) Both approaches are applied in non-human animal research, and they are not necessarily mutually exclusive but can be integrated (e.g. localizing discrete emotional states within the valence and arousal dimensions)[2]. Highly social domestic animals who are closely integrated into human social networks[30], and the human environment can be considered the natural ecological niche of this species[31] This close cohabitation requires safe interactions between humans and dogs, for which we need to interpret dogs’ behavioural expressions correctly[32]. The dog provides a unique non-primate model for studying emotional expressions that are of interest to humans
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