Abstract
Sequences of pulses can reliably communicate temporal information, but are pulses from all modalities equivalent in this regard? For an answer, we examined temporal sensitivity with visual (V) and vibrotactile (T) pulses. In Experiment One, human subjects received sequences of ten V or T pulses. Subjects categorized each sequence as slow (mean = 4 Hz) or fast (mean = 6 Hz). In different conditions, inter-pulse intervals were either fixed (isochronous sequences) or perturbed to different levels by Gaussian temporal-domain noise. Signal detection analysis showed that tactile sensitivity was superior to visual sensitivity, and that for all but the most variable sequences, subjects were biased to label V sequences “fast” more often than T sequences. We hypothesized that this bias arose from vision’s comparatively poorer temporal acuity. In Experiment Two, we used the same stimuli in a gap detection task for a direct measure of temporal acuity. We also included a bi-sensory (VT) condition to test for an effect of bimodal cue combination. On each trial, subjects observed a pair of stimuli from the same modality condition: a single-pulse stimulus, and a double-pulse stimulus whose inter-pulse interval varied from 2-32 ms. Subjects judged which trial interval contained the double-pulse stimulus. Modality-specific gap detection thresholds showed that to successfully discriminate single-pulse from double-pulse stimuli, subjects needed longer intervals between successive V pulses than between T or VT pulses. Gap detection thresholds were similar for T and VT stimuli, suggesting that the vibrotactile component dominated bimodal gap detection. Together, these results suggest that vibrotactile temporal sensitivity is superior to visual temporal sensitivity, and that vision may be relatively limited in its ability to convey rate information reliably.