Distinguishability of periodic haptic stimuli in the frequency domain

A current issue in human-computer interaction is the design of haptic stimuli. Recent studies reported that humans can successfully recognize various haptic stimuli, and thus suggest methods of designing distinguishable haptic stimuli. However, such methods have been complicated and inconsistent, indicating a need for exploring different parameters associated with human perception. Therefore we conducted this pilot study on the distinguishability of haptic stimuli. We took advantage of frequency domain analysis to explore the potential of a parameter of relative percent power difference (%PD). The Fourier series was used to design a range of synthetic haptic stimuli using approximations of square and saw-tooth signals of the same fundamental frequency and amplitude. The stimuli differed by the range of harmonic components in each series. Preliminary results revealed that stimuli based on the saw-tooth signal were more distinguishable than their square based counterparts. While investigating the parameter of %PD to measure differentiability, we observed that participants had more difficulty in distinguishing stimuli with smaller relative %PD than stimuli with greater relative %PD. A considerable change of differentiability between 10 and 35 %PD pointed towards potential just-noticeable-difference for distinguishability. Further investigation is needed to support these findings.