Does the asymmetry effect inflate the temporal expansion of odd stimuli?

Tse et al. (Percept Psychophys 66:1171-1189, 2004) reported that participants tend to overestimate the duration of an oddball stimulus. The size of this effect was much larger than the one reported by Ulrich et al. (Psychol Res 70:77-87, 2006). More crucially, the effect in the study of Tse et al. already emerged at short standard durations, arguing against the arousal account proposed by Ulrich et al. This study investigated whether the oddball effect reported by Tse et al. was inflated by an asymmetry effect, that is, by an asymmetrical distribution of physical comparison durations around the duration of the standard. Experiment 1 demonstrated that an asymmetry effect could mimic an oddball effect. Therefore, we conducted Experiment 2 to replicate the results by Tse et al. employing not only their original procedure but also an adaptive procedure that rather avoids an asymmetry effect. Both psychophysical procedures in this experiment revealed an oddball effect, which, however, was of smaller size than the one reported by Tse et al. Furthermore, this effect emerged only at longer standard durations, which is in agreement with the arousal account as the underlying mechanism of this robust temporal illusion.