Investigating the Perception of Shape-Changing Haptic Interfaces

This work addresses the lack of standardized, com parable psychophysical evaluations for shape-changing haptic interfaces (SCHIs). Given the complexity and diversity of dynamic shape-change stimuli, we developed three high-resolution, stimulus-targeting test devices that predominantly evoke one of the following three: translational or rotational surface misalignment (both cutaneous perception), or expansive motions (kinesthetic perception). Psychophysical experiments measured their Point of Subjective Equality (PSE), Just-Noticeable Difference (JND), and Weber Fraction (WF) across various transformation magnitudes, directions, and grasp types. These quantitative results were supported by nonparametric bootstrapping, providing robust statistical estimates, and enriched with qualitative user feedback collected through questionnaires. The results show that larger transformations consistently yielded significantly lower WFsfor all three devices, indicating improved relative perceptual sensitivity at larger magnitudes. This suggests non-constant WF behavior over the tested range, rather than the approximately constant WF across stimulus levels expected under Weber's law. Several device- and interaction-level factors may plausibly contribute to this, including changes in contact geometry and greater joint involvement at larger shape transformations. Furthermore, no directional bias was observed for either surface misalignment device; however, a non-significant preference for expanding motion emerged in the expansion device. Together, these findings provide an applied psychophysical characterization of the present device implementations, offer study-grounded design parameters for devices leveraging the three investigated stimulus types, and motivate extending similar investigations to additional shape-change-evoked stimuli.