The duration of rare stimuli (oddballs) presented within a stream of homogenous standards tends to be overestimated. This temporal oddball effect (OE) has been attributed to perceptual processes. The OE is usually assessed with a comparative judgment task. It has been argued, however, that this task is prone to decision biases. The present experiments employed comparative and equality judgments, since it has been suggested that equality judgments are less vulnerable to such biases. Experiments 1a and 1b used visual stimuli, and Experiment 2 auditory stimuli. The results provide no strong evidence for decision biases influencing the OE. In addition, computational modeling clearly suggests that the equality judgment is not particularly suited to distinguish between perceptual and decisional effects. Taken together, the pattern of the present results is most consistent with a perceptual origin of the OE.