Dogs and humans respond to emotionally competent stimuli by producing different facial actions

Abstract

The commonality of facial expressions of emotion has been studied in different species since Darwin, with most of the research focusing on closely related primate species. However, it is unclear to what extent there exists common facial expression in species more phylogenetically distant, but sharing a need for common interspecific emotional understanding. Here we used the objective, anatomically-based tools, FACS and DogFACS (Facial Action Coding Systems), to quantify and compare human and domestic dog facial expressions in response to emotionally-competent stimuli associated with different categories of emotional arousal. We sought to answer two questions: Firstly, do dogs display specific discriminatory facial movements in response to different categories of emotional stimuli? Secondly, do dogs display similar facial movements to humans when reacting in emotionally comparable contexts? We found that dogs displayed distinctive facial actions depending on the category of stimuli. However, dogs produced different facial movements to humans in comparable states of emotional arousal. These results refute the commonality of emotional expression across mammals, since dogs do not display human-like facial expressions. Given the unique interspecific relationship between dogs and humans, two highly social but evolutionarily distant species sharing a common environment, these findings give new insight into the origin of emotion expression.

Perception of dynamic facial expressions of emotion between dogs and humans

“…This too does not match the FACS-coded AUs with potential emotional content of the facial expression. For example, humans focused more on dogs' eyes and mouth in happiness, whereas its core AU appears only on the mouth (Caeiro et al 2017). This is consistent with the finding that similar brain activation occurs when viewing the faces of both species (Blonder et al 2004); i.e., it seems that a human-like facial search strategy is used to perceive dog faces.…”

“…Certainly, in relation to emotionally neutral dog faces, humans show a similar gaze distribution to when observing a human face (Guo et al 2010), and this might indicate a wider use of strategies developed for human face assessment in the evaluation of the faces of other species. Although Caeiro et al (2017) found unique relationships between certain AUs and specific emotionally competent triggers, we do not know whether any dog AU combinations are unique to specific emotional states, as occurs in humans; or to what extent humans attend to any of these AUs when dogs are emotionally aroused.…”

“…This is an important difference from human gaze behaviour and may reflect the significance given to the ears, frontalis, and mouth as potentially informative regions for dogs. Indeed, ears and mouth in dogs have been found to display diagnostic AUs for happiness, positive anticipation, and fear (Caeiro et al 2017). However, we cannot be sure if they are looking more at the frontalis, because it is an informative region in humans and potentially dogs (as discussed above) or if it stems from direct eye contact avoidance.…”

“…Twenty videos of human and dog faces displaying four spontaneous and naturalistic facial responses to emotionally competent stimuli for fear, happiness, positive anticipation, and frustration, plus a neutral control (see Caeiro et al 2017 and ESM 4, 5 for more stimuli details and stimuli examples) were played to the participants. Facial expressions were selected to contain the core AUs of each emotion, according to Caeiro et al (2017). Two videos per emotion and per species were displayed.…”

“…Being able to effectively recognise the emotional expression of another may thus confer a fitness benefit. However, inter-species emotion recognition potentially poses a challenge for individuals, as the context-specific emotional cues can be intra-specific (e.g., Caeiro et al 2017). The human-dog dyad is an ideal model to study intra-specific perception of emotional cues, due to their shared history and ecological niche (Skoglund et al 2015), and potential cognitive co-evolution (Hare 2007).…”