The statistical relation between two events influences the perception of how well one event relates to the presence or absence of another. The simultaneous absence of both events, just like their mutual occurrence, is theoretically relevant for describing their contingency. However, humans tend to weight co-occurring information more heavily than co-absent information. We explored the relevance of co-absent events by varying the duration and frequency of trials without stimuli. In three

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... nts, we used a rapid trial streaming procedure, and found that the perceived association between events is enhanced with increased frequency of co-absent events. Duration of co-absent events did not play as strong role on judgments of association as did frequency. These findings suggest ways in which the benefits of trial spacing, which are effectively co-absence events, could be preserved without increasing total training time. Specifically, the present results suggest that the benefits of distributed practice can be obtained without increasing the length of the training session by shortening the intervals between events. We also discuss five potential accounts of how the co-absent experience is processed: contingency sensitivity, a memory testing effect, associative interference, reduced cognitive load, and consolidation.