Evaluating the accuracy of facial expressions as emotion indicators across contexts in dogs

Abstract

Facial expressions potentially serve as indicators of animal emotions if they are consistently present across situations that (likely) elicit the same emotional state. In a previous study, we used the Dog Facial Action Coding System (DogFACS) to identify facial expressions in dogs associated with conditions presumably eliciting positive anticipation (expectation of a food reward) and frustration (prevention of access to the food). Our first aim here was to identify facial expressions of positive anticipation and frustration in dogs that are context-independent (and thus have potential as emotion indicators) and to distinguish them from expressions that are reward-specific (and thus might relate to a motivational state associated with the expected reward). Therefore, we tested a new sample of 28 dogs with a similar set-up designed to induce positive anticipation (positive condition) and frustration (negative condition) in two reward contexts: food and toys. The previous results were replicated: Ears adductor was associated with the positive condition and Ears flattener, Blink, Lips part, Jaw drop, and Nose lick with the negative condition. Four additional facial actions were also more common in the negative condition. All actions except the Upper lip raiser were independent of reward type. Our second aim was to assess basic measures of diagnostic accuracy for the potential emotion indicators. Ears flattener and Ears downward had relatively high sensitivity but low specificity, whereas the opposite was the case for the other negative correlates. Ears adductor had excellent specificity but low sensitivity. If the identified facial expressions were to be used individually as diagnostic indicators, none would allow consistent correct classifications of the associated emotion. Diagnostic accuracy measures are an essential feature for validity assessments of potential indicators of animal emotion.

Audience effect on domestic dogs’ behavioural displays and facial expressions

“…Following the experimental paradigm by Bremhorst and colleagues 28 , 29 , 49 , we tested adult dogs in a situation of anticipation of food delivery and in two situations of frustration during which food was visible but unavailable to dogs and either 1) no human was visible, or 2) a female human was looking at the dog. Furthermore, we collected cortisol saliva samples before and after each test.…”

“…In domestic dogs, previous research has identified several behavioural patterns and facial expressions as being indicative of negative affective states. Regarding facial expressions, backwards directed ears, tongue out and showing the sclera (“whale eye”) have been observed in a fear-related context (fireworks exposition 27 ) while flattened ears, lips part, jaw drop and the facial displacement behaviours of lips/nose lick and blink have been linked to frustration-evoking situations 28 , 29 . However, lips licking and nose lick have also been associated with positive anticipation situations, suggesting a link to general arousal (not specifically carrying a negative valence) 30 .…”

“…While the presence of the food didn’t have any influence on the behaviour, the “inner brow raiser” and the “tongue show” were positively influenced by the attentional state of the experimenter. However, evidence is mixed 29 and limited to only few behavioural and facial displays (Inner Brow Raiser, play signals, showing behaviour).…”

“…To achieve our goal, we adopted an experimental paradigm previously used to investigate differences in facial expressions during positive anticipation and frustration situations in dogs when waiting for a reward 28 , 29 , 49 . The basic setup involves a dog seeing a piece of food placed on a table behind a plexiglass screen.…”

Disentangling help-seeking and giving up: differential human-directed gazing by dogs in a modified unsolvable task paradigm

“…When an alternative is available, both interaction with the task and gazing appear to reflect motivation to obtain the inaccessible reward, with the preferred reward type differing between subjects (c.f. Bremhorst et al 2018 , 2021 ). Conversely, when no alternative is available, ‘looking back’ probably partly reflects help-seeking and partly giving up, leading to the observed negative correlations in this and other studies (Marshall-Pescini et al 2017 ; Udell 2015 ).…”