Exploring melodic variance in rhythmic haptic stimulus design

Haptic icons are brief, meaningful tactile or force stimuli designed to support the communication of information through the often-underutilized haptic modality. Challenges to producing large, reusable sets of haptic icons include technological constraints and the need for broadly-applicable and validated design heuristics to guide the process. The largest set of haptic stimuli to date was produced through systematic use of heuristics for monotone rhythms. We hypothesized that further extending signal expressivity would continue to enhance icon learnability. Here, we introduce melody into the design of rhythmic stimuli as a means of increasing expressiveness while retaining the principle of systematic design, as guided by music theory. Haptic melodies are evaluated for their perceptual distinctiveness; experimental results from grouping tasks indicate that rhythm dominates user categorization of melodies, with frequency and amplitude potentially left available as new dimensions for the designer to control within-group variation.