Illusion Spaces in VR: The Interplay Between Size and Taper Angle Perception in Grasping

TL;DR

This work tackles the challenge of delivering high-resolution haptic feedback in VR by examining how physical proxy geometry (size) and taper shape (angle) interact in perception. Using a 2AFC psychophysical design with 40 participants and a range of physical and virtual object pairings, the authors construct a multi-dimensional illusion space that characterizes how virtual properties can be represented by physical proxies. They derive comprehensive threshold functions and present a mathematical framework, including a four-threshold system and an online calculator, to predict representable virtual objects from given physical geometries. The findings reveal robust interdependencies: increasing virtual size expands perceived angle, while increasing virtual angle reduces perceived size, offering practical guidelines for passive haptic design and the development of proxy-based VR haptics with expanded perceptual coverage.

Abstract

Leveraging the integration of visual and proprioceptive cues, research has uncovered various perception thresholds in VR that can be exploited to support haptic feedback for grasping. While previous studies have explored individual dimensions, such as size, the combined effect of multiple geometric properties on perceptual illusions remains poorly understood. We present a two-alternative forced choice study investigating the perceptual interplay between object size and taper angle. We introduce an illusion space model, providing detailed insights into how physical and virtual object configurations affect human perception. Our insights reveal how, for example, as virtual sizes increase, users perceive that taper angles increase, and as virtual angles decrease, users overestimate sizes. We provide a mathematical model of the illusion space, and an associated tool, which can be used as a guide for the design of future VR haptic devices and for proxy object selections.

Figures (10)

• Figure 1: Physical objects for grasping. The dimensions of the objects are introduced on the top-left figure, and the following five figures are the physical objects in our experiment.
• Figure 2: Figures showcasing the experimental setup. Left: the study apparatus, including the participant's seating position, Optitrack setup for object tracking, and physical object markers. Right: the virtual view before grasping (highlighting the red center line) and during grasping.
• Figure 3: Proportion of choosing "virtual smaller". Blue areas show instances configurations in which the illusion holds, where grey areas indicate cube pairings where the illusions break.
• Figure 4: Proportion of choosing "virtual less tilted". Blue areas show instances configurations in which the illusion holds, where grey areas indicate cube pairings where the illusions break.
• Figure 5: Size perception results with congruent virtual angles. Graphs show the point of subjective equality (PSE) and upscaling and downscaling thresholds (UT and DT, respectively). The sigmoid function coefficients of each curve are provided.