Perceptual robustness of stochastic visual, vibrotactile, and bimodal stimuli
In a study of perceptual robustness, 23 subjects discriminated between two rates (3 and 6 Hz) at which brief visual, vibrotactile, or concurrent visual and vibrotactile pulses were presented. On two-thirds of the trials, inter-pulse intervals (IPIs) were stochastic, perturbed by random samples from a zero-mean Gaussian distribution. Directional changes in IPIs increased or diminished the likelihood of confusing the pulse rates, making it possible to gauge the influence of successive IPIs on subjects’ judgments. Logistic regression revealed a strong primacy effect: subjects’ decisions were disproportionately influenced by a trial’s initial IPIs. Both response times and drift-diffusion model parameter estimates indicated that information accumulates more rapidly with bimodal stimulation than with either unimodal stimulus. Error analysis suggested consistent reliance on statistically optimal decision criteria. Finally, rate information delivered by vibrotactile signals proved just as robust as information conveyed by visual signals, confirming vibrotactile stimulation’s potential for timely communication.