Life-Sized Virtual Health Coaches in VR: Rapport-Building Behaviors and Their Effects on Health Attitudes and Proxemics

Abstract

Access to effective health behavior change counseling remains limited, motivating scalable alternatives such as embodied conversational agents (ECAs). Virtual reality (VR) uniquely enables life-sized, spatially co-present ECAs that users can treat as genuine social partners, making interpersonal distance physically meaningful in ways that 2D screen deployments cannot support. We designed life-sized virtual health coaches that deliver brief motivational interviewing-inspired counseling and compared a rapport-building condition, incorporating relational dialogue, self-disclosure, affiliative humor, and agent-initiated proxemic approach, against a stationary, task-focused control. In a counterbalanced within-subjects study (N=40), participants showed short-term improvements in self-reported TTM-based health attitudes, with greater motivation gains following the rapport-building condition. Self-reported trust and working alliance with the agent were high in both conditions and did not significantly differ. Critically, a behavioral approach-distance task revealed that participants stood reliably closer to the agent following the rapport-building interaction, indicating that behavioral proxemics can complement self-report measures in capturing relational responses. Qualitative interviews showed that users interpreted agent approach as a meaningful relational signal, while highlighting the importance of timing, pacing, and boundary negotiation. We discuss design implications for rapport-aligned proxemic behaviors in life-sized VR health coaching agents.