Can you read my poker-face? Adapting the still-face paradigm to explore dog's interspecific communication.

Domestic dogs rely on a sophisticated repertoire of visual displays to regulate social interactions. However, the interpretation of some of these displays, such as facial expressions, remain unclear. In the present study, we investigated the communicative strategies dogs’ employ to re-establish a positive interaction with humans. We adopted a modified version of the classical Still-Face Paradigm and introduced two non-responsive phases: the classical “still-face” phase (human attentive but unresponsive) and a novel “face-away” phase (human turned away and inattentive) to test the flexibility of communicative signals modalities used by dogs. The test was conducted with both the owner (attachment figure) and a familiar human (familiar dog trainer). Results showed that dogs displayed a rich repertoire of visual and facial signals, which may serve affiliative and communicative functions, particularly during the first interaction and, overall, more towards their owner compared to the familiar human. Confirming a still-face effect, the frequency and duration of these behaviours significantly decreased in the non-responsive phases, compared to the first interaction. Contrary to our predictions, no differences emerged between the still-face and face-away phases and the exhibition of signals generally decreased in subsequent phases indicating a possible carry over effect. The higher communicative persistence towards the owner compared to the familiar human underscores the crucial role of the attachment bond in shaping the dog’s communicative strategies. These findings highlight the attachment bond as a key factor in interspecific communication, extend current research on the still-face paradigm in domestic dogs, and provide a valuable methodological tool for future investigations.