Perceived Frequency of Aperiodic Vibrotactile Stimuli Depends on Temporal Encoding

Mechanical transients and events arising during dexterous manipulation are detected by tactile afferents. Naturally occurring vibrotactile stimuli have a mix of frequencies, which creates complex afferent discharge patterns. Psychophysical correlates of these complex discharge patterns could be useful tools to gain greater insights into tactile coding and the principles of signal processing in the nervous system. In a previous study, we discovered that frequency perception of periodic bursting stimuli depended on the duration of the silent gap between spike bursts. Here, we investigated the perceived frequency of aperiodic vibrotactile stimuli. We found that perceived frequency was lower than the mean discharge rate of the afferents. This supports a hypothesis stemming from our previous work, that within spike trains consisting of mixed length inter-spike intervals, the contribution of a given interval to perceived frequency is weighted by its length. Thus, the present study reveals that frequency perception of both periodic and aperiodic stimuli is encoded by sophisticated processing of individual inter-spike intervals, rather than based on detection of periodicity or spike counting.