It's about time: Delay-dependent forgetting of item- and contextual-information

Once fiercely rejected, the notion of delay-dependent forgetting from long-term memory has recently resurfaced. By this notion, the duration of the study-test delay predicts the magnitude of memory degradation. Our Representation Theory of Forgetting adopts the notion of delay-dependent forgetting, alongside interference due to similarity of representations as an additional cause of forgetting—rather than its sole cause, as has been largely argued in the past. This theory maintains that the causes of forgetting depend on the underlying memory representations. Because hippocampus-based memory representations are relatively distinct from one another, by the virtue of being associated with distinct contexts, they are not as likely as non-hippocampus representations to be forgotten due to interference from similar memories. Instead, as neurobiological evidence suggests, these representations may be forgotten over the passage of time. Thus, contextual-information should be particularly sensitive to delay-dependent forgetting in comparison to item-information. In the current study we tested this hypothesis by comparing the effects of short study-test delay (~2 min) to long delay (~15 min) on forgetting. In three experiments using three different memory paradigms, we obtained various measures of item- and contextual-information. Results converged to support our predictions: whereas most measures of contextual-information showed forgetting over time, item-information was less affected by delay and, at times, was not affected at all. Finally, different patterns of time-dependent forgetting of contextual-information were observed in recall and recognition, in line with the different roles of context in these tests. Our results provide novel evidence for the specific effects of delay on hippocampus-based, contextual memory representations.