Benefitting from trial spacing without the cost of prolonged training: Frequency, not duration, of trials with absent stimuli enhances perceived contingency

The statistical relation between two events influences the perception of how one event relates to the presence or absence of another. Interestingly, the simultaneous absence of both events, just like their mutual occurrence, is relevant for describing their contingency. In three experiments, we explored the relevance of co-absent events by varying the duration and frequency of trials without stimuli. We used a rapid trial streaming procedure, and found that the perceived association between events is enhanced with increasing frequency of co-absent events unlike the duration of co-absent events which had little effect. These findings suggest ways in which the benefits of trial spacing, during which both events are absent, could be obtained without increasing total training time. Centrally, this can be done by frequent repeating of shortened co-absent events, each marked by a trial contextual cue. We discuss four potential accounts of how co-absent experience might be processed contributing to this effect: i) contingency sensitivity, ii) testing effect, iii) reduced associative interference by the context, and iv) reduced encoding interference