triMorph: Bridging Shape-Change and Cross-Sensory Correspondences for Haptic Interaction

Cross-sensory correspondences provide opportunities for designing rich sensory HCI, with prior work showing that features such as roundness and sharpness are systematically linked to language, color, sound, and emotion. Yet two challenges remain: few technologies can dynamically transition between these features, and little is known about the thresholds at which a form is judged as sufficiently rounded or spiky to realize these cross-sensory effects. We present triMorph, a pneumatic shape-changing interface capable of smoothly morphing between spiky, flat, and rounded configurations. In a psychophysical study with 30 participants, we quantified perceptual accuracy and precision in mapping triMorph shapes to visual-linguistic categories and examined shape–color and shape–emotion correspondences. Results reveal threshold values for reliable categorization, with rounded shapes linked to pleasant emotions and lighter colors, and spiky shapes to arousal and darker tones. Our findings provide empirical foundations and design guidelines for grounding shape-changing artifacts more firmly in cross-sensory cognition.