We set out to test whether positive non-verbal behaviours of a virtual coach can enhance people's engagement in automated virtual reality therapy. 120 individuals scoring highly for fear of heights participated. In a two-by-two factor, between-groups, randomised design, participants met a virtual coach that varied in warmth of facial expression (with/without) and affirmative nods (with/without). The virtual coach provided a consultation about treating fear of heights. Participants rated the therapeutic alliance, treatment credibility, and treatment expectancy. Both warm facial expressions (group difference = 7.44 [3.25, 11.62], p = 0.001, $${eta}_{p}^{2}$$ eta p 2 =0.10) and affirmative nods (group difference = 4.36 [0.21, 8.58], p = 0.040, $${eta}_{p}^{2}$$ eta p 2 = 0.04) by the virtual coach independently increased therapeutic alliance. Affirmative nods increased the treatment credibility (group difference = 1.76 [0.34, 3.11], p = 0.015, $${eta}_{p}^{2}$$ eta p 2 = 0.05) and expectancy (group difference = 2.28 [0.45, 4.12], p = 0.015, $${eta}_{p}^{2}$$ eta p 2 = 0.05) but warm facial expressions did not increase treatment credibility (group difference = 0.64 [− 0.75, 2.02], p = 0.363, $${eta}_{p}^{2}$$ eta p 2 = 0.01) or expectancy (group difference = 0.36 [− 1.48, 2.20], p = 0.700, $${eta}_{p}^{2}$$ eta p 2 = 0.001). There were no significant interactions between head nods and facial expressions in the occurrence of therapeutic alliance (p = 0.403, $${eta}_{p}^{2}$$ eta p 2 = 0.01), credibility (p = 0.072, $${eta}_{p}^{2}$$ eta p 2 = 0.03), or expectancy (p = 0.275, $${eta}_{p}^{2}$$ eta p 2 = 0.01). Our results demonstrate that in the development of automated VR therapies there is likely to be therapeutic value in detailed consideration of the animations of virtual coaches.

Virtual reality (VR) simulations with virtual characters have been increasingly deployed to understand context-based human behaviour. The current study investigated the effects of perceived agency of the other players, who were either (human-controlled) avatars or (computer-controlled) agents, on the player's overall presence levels (with 3 subscales of spatial presence, involvement, and realism). We also tested the relationship between the player's perception of the agency of the other players, in-game prosocial behaviour (voluntary behaviour to help other players) and their own real-life prosocial traits. 32 university students played a VR game with agents, but half the participants were told they were playing with avatars (an experimental deception). The group who were told they were playing with other humans had higher overall presence than the group who knew they were playing with agents, due to increased spatial presence and involvement. While there was no direct link between the player's perceived agency of the other players and their own in-game behaviours, higher prosocial scores increased their chance of helping the other players in the agent group. Overall, this study suggests that multi-player VR experiences (or those purported to be multiplayer) lead to greater influence on people's psychological and behavioural reactions over singleplayer experiences.

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