Persistence of the spacing effect in free recall under varying incidental learning conditions.

In three incidental learning experiments, an attempt was made to eliminate the processing deficit under massed presentation that is assumed to be responsible for the spacing effect in free recall, according to the attenuation of attention hypothesis. This was to be accomplished in Experiment I by requiring subjects to attend specifically to the total exposure duration of each item and in Experiments II and III by requiring subjects to rate the successive occurrences of repeated items on different semantic rating scales. The results of the three experiments consistently showed that these manipulations were ineffective in eliminating the spacing effect. Subsidiary analyses indicated that the activities involved in doing the semantic rating tasks do not provide direct access to retrieval cues useful for subsequent recall. Instead, it appears that, in order to perform the semantic rating tasks reliably, subjects must compare the to-be-rated item with previously rated items, and this comparison process may serve as the source of retrieval cues for subsequent recall.