Abstract
As humanoid robots become more advanced and commonplace, the average user may perceive their robotic companion as human-like entities that can make social decisions, such as the deliberate choice to act fairly or selfishly. It is important for scientists and designers to consider how this will affect our interactions with social robots. The current paper explores how social decision making with humanoid robots changes as the degree of their human-likeness changes. For that purpose, we created a spectrum of human-like agents via morphing that ranged from very robot-like to very human-like in physical appearance (i.e., in increments of 20%) and measured how this change in physical humanness affected decision-making in two economic games: the Ultimatum Game (Experiment 1) and Trust Game (Experiment 2). We expected increases in human-like appearance to lead to higher rates of punishment for unfair offers and higher ratings of trust in both games. While physical humanness did not have an impact on economic decisions in either of the ex-periments, follow-up analyses showed that both subjective ratings of trust and agent approachability medi-ated the effect of agent appearance on decision-making in both experiments. Possible consequences of these findings for human-robot interactions are discussed.