Gaze behaviour as a visual cue to animacy

A characteristic that distinguishes biological agents from inanimate objects is that the former can have a direction of attention. While it is natural to associate a person’s direction of attention with the appearance of their face, attentional behaviours are also a kind of relational motion, in which an entity rotates a specific axis of its form in relation to an independent feature of its environment. Here, we examined whether gaze-like motion behaviours provide a visual cue to animacy independent of the human form. We generated animations in which the rotation of a geometric object (the agent) was dependent on the movement of a target. Participants made judgements about how creature-like the objects appeared, and these were highly sensitive to the correspondence between objects over and above their individual motion. We varied the dependency between agent rotation and target motion in terms of temporal synchrony, temporal order, cross-correlation, and the complexity of their shared trajectory. These affected the perceived animacy of the agent to differing extents. When the behaviour of the agent was driven by a model of predictive tracking that incorporates a sensory sampling delay, perceived animacy was broadly tuned across changes in rotational behaviour induced by the sampling delay of the agent. Overall, the tracking relationship provides a salient cue to animacy independent of biological form, provided that temporal synchrony between objects is within a certain range. This motion relationship may be one to which the human visual system is highly-attuned, due to its association with attentional behaviour and the presence of other minds in our environment.