Information Transfer on the Wrist: Vibrotactile Signal Characteristics from Single to Multiple Tactors

Vision and sound often dominate human-robot interaction systems, but touch can convey nuanced, real-time task and environment information. Vibrotactile feedback is increasingly common in commercial devices, and the wrist offers a promising location for wearable haptics: it is unobtrusive and sensitive to tactile input. While prior work has studied vibrotactile feedback in navigation and action confirmation tasks, quantifying information transfer for wrist-worn vibrotactile cues remains underexplored. This study estimates information transfer on the wrist (bits per stimulus) using a confusion-matrix-based metric alongside accuracy and pleasantness ratings. We conducted three linked studies with the same participants: identifying single-tactor cues spanning frequency, amplitude, and modulation; identifying the same cues under sequential vibrotactile masking and during a concurrent typing task; and identifying multi-tactor spatiotemporal patterns and rating pleasantness. Participants reliably discriminated complex signals, with amplitude and feature interactions playing key roles. Information transfer ranged from 0.75 bits/stimulus for multi-tactor patterns to 2.28 bits/stimulus for single-tactor testing across all participants (2.56 for experienced participants); masking and typing yielded 1.64 and 1.85 bits/stimulus, respectively. Performance was not solely driven by amplitude-normalized intensity.