Estimating Detection Thresholds for Desktop-Scale Hand Redirection in Virtual Reality

Abstract

Virtual reality (VR) interaction techniques like haptic retargeting offset the user's rendered virtual hand from the real hand location to redirect the user's physical hand movement. This paper explores the order of magnitude of hand redirection that can be applied without the user noticing it. By deriving lower-bound estimates of detection thresholds, we quantify the range of unnoticeable redirection for the three basic redirection dimensions, horizontal, vertical and gain-based hand warping. In a two-alternative forced choice (2AFC) experiment, we individually explore these three hand warping dimensions each in three different scenarios: a very conservative scenario without any distraction and two conservative but more realistic scenarios that distract users from the redirection. Additionally, we combine the results of all scenarios to derive robust recommendations for each redirection technique. Our results indicate that within a certain range, desktop-scale VR hand redirection can go unnoticed by the user, but that this range is narrow. The findings show that the virtual hand can be unnoticeably displaced horizontally or vertically by up to 4.5° in either direction, respectively. This allows for a range of ca. 9°, in which users cannot reliably detect applied redirection. For our gain-based hand redirection technique, we found that gain factors between g = 0.88 and g = 1.07 can go unnoticed, which corresponds to a user grasping up to 13.75% further or up to 6.18% less far than in virtual space. Our findings are of value for the development of VR applications that aim to redirect users in an undetectable manner, such as for haptic retargeting.