ThumbShift: Modulating Perceived Object Properties through Dynamic Thumb Repositioning

Inspired by the observation that humans naturally adjust finger configurations based on object size and weight, we present ThumbShift, a novel haptic controller that physically moves and rotates the user's thumb to render subtle shifts in finger collaboration and affect whole-hand grasp perception. Unlike prior work focused on grasp type or global haptic feedback, our approach uniquely targets finger collaboration variation through localised, real-time finger repositioning during grasp - enabling Dynamic Digit Positioning (DDP) to modulate haptic and perceptual experience. Results of our user studies show that while size perception changes only slightly, by about 5%, in a two-alternative forced choice (2AFC) task, perceived weight shifts significantly—by approximately 19%—in magnitude estimation tasks. We also report on the influence of mass centre position which extends the weight perception changing ability to about 56%, and how finger force distribution works in altering users' perception. These findings demonstrate that dynamic thumb movement can reconfigure force distribution across the hand and substantially alter haptic experience. By highlighting the underexplored role of digit motion in object perception, our work opens new directions for perception-aware haptic devices in VR, AR, and physical interaction design.