Pseudo-Haptics for Lowering Movements: Enhancing Perceived Weight via Initial Lifting Phase Modulation

Weight perception is essential for realistic object manipulation in Virtual Reality (VR). While pseudo-haptics effectively simulates perceived weight during lifting, its application to lowering movements remains unexplored. This study investigates the direction-dependent characteristics of pseudo-haptic weight perception and proposes a novel method for lowering movements. In Experiment 1 (N=20), we compared the effects of visual gain manipulation on lifting and lowering. The results revealed that the pseudo-haptic effect was significantly weaker in lowering than in lifting, with large individual differences. Qualitative analysis suggested that slowing down the lowering motion (low gain) conflicts with users' intuitive physics of gravity, leading to reduced realism. To address this, Experiment 2 (N=24) introduced a method that applies a visual delay specifically to the brief "initial lifting phase" that naturally occurs before lowering. By inducing a heaviness impression during this initial transient (a few centimeters in our setup), we aimed to establish an initial estimate of heaviness that anchors subsequent weight perception during lowering. The results showed a significant main effect of initial lifting delay on perceived heaviness ($p \lt .0001, \eta _{p}^{2} = 0.84$). Furthermore, qualitative analysis indicated that this anchored heaviness estimate modulated how later lowering kinematics were interpreted: high-gain lowering could be assimilated as evidence of heaviness when it was compatible with the intuitive mass-speed belief (i.e., the expectation that heavier objects fall faster). Our findings suggest that temporally separating the establishment of an initial heaviness estimate from the subsequent lowering behavior is a promising approach for enhancing perceived weight in lowering movements in VR.