From Message to Expression: Exploring Non-Verbal Communication for Appearance-Constrained Robots

Human-robot communication is key to establishing transparency of robot states, and promoting psychological safety of the people interacting with a robot. Such communication is especially challenging for appearance-constrained robots, as they do not afford to employ commonly-used an-thropomorphic modalities such as facial expressions. We explore how an appearance-constrained quadruped robot can use LEDs and gestures to generate affective expressions in order to non-verbally communicate. Traditionally, affect has been used as a signalling paradigm in Human-Robot Interaction where expressions are designed with the goal of communicating a particular emotion such as happiness. Instead, this work explores a generalizable mapping from informative messages (e.g., "I am listening") to abstract affective expressions. We modulate the expressions by a model of affect, taking inspirations from Affect Control Theory (ACT). To explore designing the expressions, we first conducted pilot semi-structured interviews consulting stakeholders who regularly operate appearance-constrained robots (N = 12) to understand the communication requirements. Then, we designed a set of six affective expressions and evaluated them in a crowdsourced study (N = 450). Findings suggest that the expressions can significantly improve effective communication of a robot’s awareness and intent, and promote psychological safety of people interacting with it.