The simultaneous oddball: oddball presentation does not affect simultaneity judgments

The oddball duration illusion describes how a rare or nonrepeated stimulus is perceived as lasting longer than a common or repeated stimulus. It has been argued that the oddball duration illusion could emerge because of an earlier perceived onset of an oddball stimulus. However, most methods used to assess the perceived duration of an oddball stimulus are ill suited to detect onset effects. Therefore, in the current article, I tested the perceived onset of oddball and standard stimuli using a simultaneity judgment task. In Experiments 1 and 2, repetition and rarity of the target stimulus were varied, and participants were required to judge whether the target stimulus and another stimulus were concurrent. In Experiment 3, I tested whether a brief initial stimulus could act as a conditioning stimulus in the oddball duration illusion. This was to ensure an oddball duration illusion could have occurred given the short duration of stimuli in the first two experiments. In both the first two experiments, I found moderate support for no onset-based difference between oddball and nonoddball stimuli. In Experiment 3, I found that a short conditioning stimulus could still lead to the oddball duration illusion occurring, removing this possible explanation for the null result. Experiment 4 showed that an oddball duration illusion could emerge given the rarity of the stimulus and a concurrent sound. In sum, the current article found evidence against an onset-based explanation of the oddball duration illusion.