Predictable and distinguishable morphing of vibrotactile rhythm

Vibrotactile (VT) icons are a ubiquitous, increasingly expressive and expected communicative element of many user interfaces, routinely deployed with technology from rumble motors to novel expressive tactile actuators. However, it is still difficult to design, customize, and experiment with VT feedback. Here we consider manipulation of one of the most salient VT design elements, rhythm, through perceptual morphing. The ability to create perceptual morphs between pairs of VT signal parents expands editorial scope and precision for designers, end-users, and hapticians. To assess perceptual morphs, we propose criteria of predictability - a morph has similarities to one or both parents; and distinguishability - a morph is different from its parents. We developed a new algorithm for perceptual rhythm morphing based on dynamic-time warping (DTW), implemented in an open-source online tool, MacaronMix. Two studies revealed limits and conditions under which DTW-produced VT rhythm morphs are predictable and distinguishable.