What influences a pet dog's first impression of a stranger?

Dogs live in the dynamic human social networks full of strangers, yet they form strong and selective bonds with familiar caretakers. Little is known about how a bond is initially formed between a dog and a complete stranger. The first-impression hypothesis suggests that interacting with strangers can present an opportunity to form a mutualistic partnership. It predicts that dogs should respond positively toward a complete stranger to facilitate bonding (Prediction 1) and adjust their preferences in response to the perceived risk and benefit of interacting with strangers (Prediction 2). We examine the social preferences of pet dogs toward a complete stranger whom they have never met before and several other potential partners - the owner with whom subjects have had a positive, long-term bond (Experiment 1), and an exposed stranger with whom they have had a positive short-term interaction (Experiment 2) or a negative one (Experiment 3). In support of Prediction 1, subjects were exceptionally trusting across contexts. Mixed results were found with regard to Prediction 2. Subjects preferred their owner over a stranger when following social cues and (to a lesser degree) when approaching and feeding in close proximity. However, relative to a complete stranger, subjects did not consistently prefer the positively exposed stranger or avoid the negatively exposed one. The lack of clear selectivity might be due to pet dogs' high baseline level of trust of complete strangers or reflect the strength of their existing bonds that negated the need for another positive bond with a new human partner.