United we fall: All-or-none forgetting of complex episodic events.

Abstract

Do complex event representations fragment over time, or are they instead forgotten in an all-or-none manner? For example, if we met a friend in a café and they gave us a present, do we forget the constituent elements of this event (location, person, and object) independently, or would the whole event be forgotten? Research suggests that item-based memories are forgotten in a fragmented manner. However, we do not know how more complex episodic, event-based memories are forgotten. We assessed both retrieval accuracy and dependency—the statistical association between the retrieval successes of different elements from the same event—for complex events. Across 4 experiments, we show that retrieval dependency is found both immediately after learning and following a 12-hr and 1-week delay. Further, the amount of retrieval dependency after a delay is greater than that predicted by a model of independent forgetting. This dependency was only seen for coherent “closed-loops,” where all pairwise associations between locations, people, and objects were encoded. When “open-loops” were learned, where only 2 out of the 3 possible associations were encoded, no dependency was seen immediately after learning or after a delay. Finally, we also provide evidence for higher retention rates for closed-loops than for open-loops. Therefore, closed-loops do not fragment as a function of forgetting and are retained for longer than are open-loops. Our findings suggest that coherent episodic events are not only retrieved, but also forgotten, in an all-or-none manner.

Progression from feature-specific brain activity to hippocampal binding during episodic encoding

“…Here, we present the encoding data from our prior work (Cooper and Ritchey, 2019) in which participants encoded and reconstructed complex events. In line with past research (Horner and Burgess, 2013;Joensen et al, 2019), we previously showed that successful recall of event associations in our task -an object with a color, scene location, and sound -exhibits a dependent structure (Cooper and Ritchey, 2019). In the current analyses, we leverage the multimodal aspect of this paradigm to test how features are prioritized and integrated during encoding.…”

Make or break it: Boundary conditions for integrating multiple elements in episodic memory

“…However, there was very A key difference between this experiment and previous studies was that we decreased trial timings at both encoding and retrieval. While previous studies have successfully shown memory dependency from separate encoding when participants were given 6 s to encode and retrieve each trial (e.g., Joensen et al, 2020), we allowed only 3 s per encoding and retrieval trial. This difference was implemented to prevent adults performing at ceiling levels in a task otherwise designed to be administered with children, but may have interfered with holistic retrieval in two ways.…”

“…Evidence of pattern completion at retrieval following the encoding of all within-event associations has since been supported by neuroimaging studies, which show that hippocampal activity at retrieval is associated with element-related neocortical activity-even for those event elements not directly tested (Grande et al, 2019;Horner, Bisby, Bush, Lin, & Burgess, 2015). Furthermore, Joensen, Gaskell, and Horner (2020) demonstrated that this retrieval dependency is consistent over time, such that events are likely forgotten in an all-or-none manner.…”

“…Third, it may have applied CONDITIONS FOR MEMORY INTEGRATION 6 benefits in understanding whether the paradigm has use outside of research contexts. The creation of such robust memory structures that are less prone to decay (Joensen et al, 2020) could benefit learning in educational settings, but would require significant adaptation to be relevant to learning real world information. Understanding and documenting the limitations of this paradigm is essential for progress in all of these domains.…”

“…If performance is very high however, then the proportion of joint retrieval in the data cannot be higher than in the independent model, and we exclude participants at ceiling performance (≥ 95%) to avoid this issue. Note that this measure of retrieval dependency is the same measure that has been used in studies demonstrating hippocampal CA3 involvement in holistic recollection (Grande et al, 2019), and provides a robust measure of event memory over time (Joensen et al, 2020).…”