Relations between timing,position, and grouping in short-term memory

This article is concerned with how information about time and position in a sequence is represented in short-term memory and expressed in the dynamics of serial recall. Temporal-distinctiveness theories of memory predict that isolating a list item in time will improve recall accuracy for that item. Although the majority of research in short-term memory has failed to demonstrate a temporal isolation effect (TIE), there are occasions on which a TIE is observed. The disparity in results has been explained by assuming that participants can adaptively weight temporal and nontemporal information at retrieval, with differences between experiments promoting or discouraging reliance on time as a source of episodic information. A particular focus of the present study is the finding that the TIE is substantially observed in standard serial recall only when participants are instructed to group the list into minisequences. The findings of two experiments using instructed grouping replicated this effect but showed that it is attributable to a longer gap at the group boundary enhancing the positive effect of grouping on recall accuracy. These results show that the hierarchical representations usually associated with temporal grouping are also elicited by instructed grouping but that an additional and nonspecific benefit to recall obtains from lengthening the pause between groups. An additional role for time is identified in the timing of responses: The dynamics of input sequences tend to be mirrored in output sequences for ungrouped lists, whereas the primacy pattern in grouped lists is for a longer duration to speed access to the following group when that duration occurs at an instructed group boundary.