Modality Differences in Timing and the Filled-Duration Illusion: Testing the Pacemaker Rate Explanation

Performance in temporal difference threshold and estimation tasks is markedly less accurate for visual intervals than for auditory intervals. In addition, thresholds and estimates are likewise less accurate for empty than for filled intervals. In scalar timing theory, these differences have been explained as alterations in pacemaker rate, which is faster for auditory and filled intervals than for visual and empty intervals. We tested this explanation according to three research aims. First, we replicated the threshold and estimation tasks of Jones, Poliakoff, and Wells (2009) and found the well-documented greater precision for auditory over visual intervals, and filled over empty intervals. Second, we considered inter-individual differences in these classic effects, and found that up to 27% of participants were found to exhibit opposite patterns. Finally, we examined intra-individual differences to investigate (i) whether thresholds and estimates correlate within each stimulus condition, and (ii) whether the stimulus condition in which a participants’ pacemaker rate was highest was in the same condition in both tasks. Here we found that if pacemaker rate is indeed a driving factor for thresholds and estimates, its effect may be greater for empty intervals, where the two tasks correlate, than for filled intervals where they do not. In addition, it was more common for participants to perform best in different modalities in each task, though this was not true of ordinal intra-individual differences for the filled-duration illusion. Overall, this research presents several findings inconsistent with the pacemaker rate explanation.