Fear of heights in virtual reality saturates 20 to 40 m above ground.

Recent epidemiological studies indicate that about one-third of the general population suffers from a more or less disabling height intolerance, with a relevant impact on quality of life in many of them. Acrophobia, the most severe form of visual height intolerance, has a life-time prevalence of around 5%. Although it is commonly believed that fear of heights should continuously aggravate with increasing elevation, this issue has not been systematically investigated yet. Here, we examined this topic using immersive virtual reality, an established tool in therapy for fear of heights, that allows to flexibly manipulate height stimuli. In a comprehensive cohort (including insusceptible subjects as well as subjects with height intolerance up to acrophobia) height intolerance severity was graded by an established metric scale (vHISS). Participants were randomly exposed to different virtual elevations using a head-mounted display. Behavioral responses to virtual height exposure were analogous to exposure in vivo. Participants exhibited increased anxiety and musculoskeletal stiffening with enhanced high-frequency body sway, to an extend that corresponded to the individual subjective height intolerance rating. For all behavioral responses, we observed a saturation above a certain altitude. Body sway and musculoskeletal stiffening became maximal at 20 m above ground, whereas anxiety saturated above 40 m. These results suggest that fear of heights is characterized by a nonlinear stimulus-response relationship and a dissociation between visual-height-induced bodily and emotional reactions.