Visual and vibrotactile temporal sensitivity: Telling time with a noisy clock

Abstract

Important characteristics of the environment can be transduced and represented in the temporal patterning of sensory stimulation. In two experiments, we compared accuracy of temporal processing by different modalities. Experiment 1 examined binary categorization of rate for visual (V) or vibrotactile (T) stimulus pulses presented at either 4 or 6 Hz. Inter-pulse intervals were either constant or variable, perturbed by random Gaussian variates. Subjects categorized the rate of T pulse sequences more accurately than V sequences. In V conditions only, subjects disproportionately tended to mis-categorize 4-Hz pulse rates, for all but the most variable sequences. We hypothesized that this pattern of errors arose because individual V pulses appeared longer in duration, disproportionately causing V sequences to appear fast. We tested this hypothesis in Experiment 2, using simpler stimuli and a two-interval forced choice method. Gap detection thresholds were taken with the same two modalities as in Experiment 1, and also with bimodal (VT) stimuli. As predicted, visual gap thresholds were larger (3×) than tactile thresholds. Additionally, performance with VT stimuli seemed to be nearly completely dominated by their T components. Together, these results suggest considerable, untapped potential for vibrotactile stimulation to convey temporal information like that needed for eyes-free alerting signals.