Still-face Effect in Dogs (Canis familiaris). A Pilot Study

Still-face effect in domestic dogs: comparing untrained with trained and animal assisted interventions dogs

The still-face effect has been extensively studied in human infants and comprises the reduction in affiliative behaviors and increased stress that occurs after a sudden interruption of social interaction with a caregiver. Domestic dogs (Canis familiaris) are model candidates for showing this effect, as they form deep bonds with their owners and interspecific social interaction is reinforcing to them. The aim of these studies was to assess if companion dogs exhibit the still-face effect and whether prior experiences during ontogeny modulate this effect. To this end, Study 1 compared dogs with different levels of training (untrained, intermediate, and advanced), while Study 2 assessed dogs that participated in Animal Assisted Interventions (AAIs) and companion dogs (CDs). The procedure was carried out virtually and comprised three phases lasting 1 min: interaction, still-face (the owner turned suddenly indifferent), and reunion (the interaction was resumed). Dogs exhibited a decrease in proximity to and contact with the owner, as well as an increase in begging and stress behaviors during the still-face phase. Moreover, this was not observed in a control condition in which the interaction continued in the same way during all three phases, discarding alternative explanations for these changes. These results show that dogs experience a still-face effect in a similar way to infants, highlighting the value interspecific social interaction has for dogs. Nevertheless, the absence of differences according to their training level or participation in AAIs suggests this is a robust phenomenon, which appears to be less susceptible to the influences of ontogenetic experiences.

What Is Written on a Dog's Face? Evaluating the Impact of Facial Phenotypes on Communication between Humans and Canines

Facial phenotypes are significant in communication with conspecifics among social primates. Less is understood about the impact of such markers in heterospecific encounters. Through behavioral and physical phenotype analyses of domesticated dogs living in human households, this study aims to evaluate the potential impact of superficial facial markings on dogs' production of human-directed facial expressions. That is, this study explores how facial markings, such as eyebrows, patches, and widow's peaks, are related to expressivity toward humans. We used the Dog Facial Action Coding System (DogFACS) as an objective measure of expressivity, and we developed an original schematic for a standardized coding of facial patterns and coloration on a sample of more than 100 male and female dogs (N = 103), aged from 6 months to 12 years, representing eight breed groups. The present study found a statistically significant, though weak, correlation between expression rate and facial complexity, with dogs with plainer faces tending to be more expressive (r = -0.326, p ≤ 0.001). Interestingly, for adult dogs, human companions characterized dogs' rates of facial expressivity with more accuracy for dogs with plainer faces. Especially relevant to interspecies communication and cooperation, within-subject analyses revealed that dogs' muscle movements were distributed more evenly across their facial regions in a highly social test condition compared to conditions in which they received ambiguous cues from their owners. On the whole, this study provides an original evaluation of how facial features may impact communication in human-dog interactions.