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Do Click Trains Dilate Time Perception due to Physiological Arousal?

Presentation of an auditory click-train before a stimulus leads to the relative overestimation of stimulus duration. This is thought to be due to an increase in the rate of the pacemaker (inferred from the slope when estimates are regressed against stimulus duration) of an internal clock, said to be triggered by physiological arousal. Work with emotional stimuli suggests similar temporal dilations, and there is (mixed) evidence suggesting this effect may be due to physiological arousal. We therefore aimed to test the assertion that click trains increase duration estimates due to increased physiological arousal. We compared estimates of tone durations following negative sounds, neutral sounds, click trains, and silence, while recording pupil size and heart rate as measures of arousal. Contrary to click train literature, estimates did not significantly differ following any of the stimulation types, possibly due to large trial baseline periods. However, pupil size change was significantly higher during negative and neutral sounds than both click trains and silence, and higher during click trains than silence. Heart rate change was higher during negative sounds than click trains. Finally, while pupil size change did not correlate with estimation slopes, heart rate change correlated with estimation slopes for neutral sounds and click trains (significantly) and negative sounds and silence (moderate and anecdotal Bayes factors respectively). In conclusion, there was evidence to suggest that click trains increased physiological arousal (pupil size) compared to silence, and that higher arousal (heart rate) during click trains correlates with estimation slopes (pacemaker rate) following click trains.