A psychophysical scale of roughness under static touch as a basis for haptic rendering calibration

While visual and auditory display technologies rely on long-established psychophysical scales, a comparable scale for tactile perception in virtual reality (VR) is not yet well established. Although roughness, a primary dimension of surface perception, is experienced under both dynamic and static touch, tactile rendering and psychophysical research have focused on dynamic touch. To address this gap, this study constructed and validated a ratio scale of perceived roughness under static touch. Participants explored 3D-printed raised-dot specimens using their index fingers and evaluated perceived roughness via cross-modality matching with the loudness of a 1000 Hz pure tone and line length. Their responses yielded a validated ratio scale. To enhance its practical utility, this scale was anchored to daily-life tactile experiences, covering a range from 2.9 to 58.3 out of 100, and was associated with familiar real-world objects. This study provides a perceptual reference for characterizing roughness under static touch. The scale may serve as a basis for future haptic rendering calibration through device-based validation and psychophysical evaluation, contributing to more realistic and consistent tactile experiences.