Design and Evaluation of a Physically Synchronized Virtual Therapist Avatar to Improve Trust in a Single-Arm Massage Robot Incorporating Skilled Massage Techniques

In human–robot interaction (HRI) involving physical contact, establishing user trust is critical—especially in applications such as robotic massage, where direct tactile stimulation can provoke anxiety. This study investigates how the visual appearance of virtual avatars influences users’ psychological and physiological responses, with the goal of identifying design strategies for enhancing trust. We developed a Virtual Reality (VR) massage system that synchronizes a robotic arm with a virtual therapist avatar and examined six avatar conditions varying in human-likeness, body size, and gender. Subjective ratings and physiological signals were collected under each condition. The results suggest three observations. First, trust is not determined solely by the avatar’s appearance but is significantly enhanced when the tactile experience is consistent with the expectations induced by that appearance. Second, trust comprises two distinct components—social and functional—which must be explicitly defined in design. Third, the avatar’s appearance affected both subjective ratings and autonomic responses, including CCV-TP-based heart rate variability, indicating that visual expectations can modulate users’ perception of physical sensations. These findings contribute to both academic understanding and practical design of HRI systems involving physical interaction, such as those used in remote healthcare and assistive robotics.