Heterogeneous Stroke: Using Unique Vibration Cues to Improve the Wrist-Worn Spatiotemporal Tactile Display
Taejun Kim, Youngbo Aram Shim, Geehyuk Lee
TL;DR
This work tackles the limited spatial resolution of wrist-worn tactile displays by introducing Heterogeneous Stroke, a design that assigns unique vibrotactile cues to each tactor to reduce positional confusion and extend the perceptual space from 1D to 2D. By combining two vibration frequencies (170 Hz and 300 Hz) with a roughness cue via amplitude modulation, the authors demonstrate high recognition accuracy for alphanumeric patterns across different arm postures, achieving 93.8% for alphabets and 92.4% for digits without extending pattern duration. The approach significantly outperforms Baseline STPs, highlights posture as a key design factor, and discusses practical actuator considerations and safety. Collectively, the findings advance reliable tactile communication on wrist-worn devices, with strong implications for wearable haptics in real-world use.
Abstract
Beyond a simple notification of incoming calls or messages, more complex information such as alphabets and digits can be delivered through spatiotemporal tactile patterns (STPs) on a wrist-worn tactile display (WTD) with multiple tactors. However, owing to the limited skin area and spatial acuity of the wrist, frequent confusions occur between closely located tactors, resulting in a low recognition accuracy. Furthermore, the accuracies reported in previous studies have mostly been measured for a specific posture and could further decrease with free arm postures in real life. Herein, we present Heterogeneous Stroke, a design concept for improving the recognition accuracy of STPs on a WTD. By assigning unique vibrotactile stimuli to each tactor, the confusion between tactors can be reduced. Through our implementation of Heterogeneous Stroke, the alphanumeric characters could be delivered with high accuracy (93.8% for 26 alphabets and 92.4% for 10 digits) across different arm postures.