How facial expressions differ in flat-faced and normal dogs

Abstract

This study develops a novel automated method for measuring continuous dynamics of dog facial behavior based on video-based tracking of 46 facial landmarks grounded in the Dog Facial Action Coding System. This method is applied for comparing the facial behavior of () brachycephalic (Boston Terrier) and () normocephalic (Jack Russel Terrier) dogs in four different contexts, eliciting various inner states: positive (play and called by name) and negative (separation and stranger). Having objectively quantified facial dynamics in brachycephalic and normocephalic dogs, we have found that brachycephalic dogs exhibited consistently lower facial dynamics across all four tested contexts and facial regions (eyes, mouth, and ears) compared to normocephalic dogs. They further demonstrated relatively higher dynamics in positive play and negative stranger conditions than in the other two conditions. In contrast, normocephalic dogs showed elevated dynamics exclusively in the positive play condition, with significantly reduced dynamics in the negative stranger condition. These findings highlight distinct patterns of facial expressivity between the two morphological groups, suggesting decreased facial expression in brachycephalic dogs and demonstrating our method's value in providing novel insights into canine communication.