The holistic forgetting of events and the (sometimes) fragmented forgetting of objects

Episodic events are typically retrieved and forgotten holistically. If you recall one element (e.g., a person), you are more likely to recall other elements from the same event (e.g., the location), a pattern that is retained over time in the presence of forgetting. In contrast, representations of individual items, such as objects, may be less coherently bound, such that object features are forgotten at different rates and retrieval dependency decreases across delay. To test the theoretical prediction that forgetting qualitatively differs across levels in a representational hierarchy, we investigated the potential dissociation between event and item memory across five experiments. Participants encoded three-element events comprising images of famous people, locations, and objects. We measured retrieval accuracy and the dependency between the retrieval of event associations and object features, immediately after encoding and after various delays (5h to 3 days). Across experiments, retrieval accuracy decreased for both events and objects over time, revealing forgetting. Retrieval dependency for event elements (i.e., people, locations, and objects) did not change over time, suggesting the holistic forgetting of events. Retrieval dependency for object features (i.e., state and colour) was more variable. Depending on encoding and delay conditions across the experiments, we observed both fragmentation and holistic forgetting of object features. Our results suggest that event representations remain coherent over time, whereas object representations can, but do not always, fragment. This provides support for our representational hierarchy framework of forgetting, however there are (still to be determined) boundary conditions in relation to the fragmentation of object representations.