Long-term memory for movie details: selective decay for verbal information at one week

Mnemonic representations of complex events are multidimensional, incorporating information about objects and characters, their interactions and their spatial-temporal context. The present study investigated the degree to which detailed verbal information (i.e., dialogues), as well as semantic and spatiotemporal (i.e., "what", "where", and "when") elements of episodic memories for movies, are forgotten over the course of a week. Moreover, we tested whether the amount of dimension-specific forgetting differed as a function of the participant's age. In a mixed design, younger and middle-aged participants were asked to watch a ∼90 min movie and provide yes/no answers to detailed questions about different dimensions of the presented material after 1, 3 days, and 1 week. The results indicate that memory decay mainly affects the verbal dimension, both in terms of response accuracy and confidence. Instead, detailed information about objects/characters' features and spatiotemporal context seems to be relatively preserved, despite a general decrease in response confidence. Furthermore, younger adults were in general more accurate and confident than middle-aged participants, although, again, the verbal dimension exhibited a significant age-related difference. We propose that this selective forgetting depends on the progressive advantage of visual compared to auditory/verbal information in memory for complex events.

Forgetting rates of gist and peripheral episodic details in prose recall

In a seminal study, Slamecka and McElree showed that the degree of initial learning of verbal material affected the intercepts but not the slopes of forgetting curves. However, more recent work has reported that memories for central events (gist) and memory for secondary details (peripheral) were forgotten at different rates over periods of days, with gist memory retained more consistently over time than details. The present experiments aimed to investigate whether qualitatively different types of memory scoring (gist vs. peripheral) are forgotten at different rates in prose recall. In three experiments, 232 participants listened to two prose narratives and were subsequently asked to freely recall the stories. In the first two experiments participants were tested repeatedly after days and a month, while in the third experiment they were tested only after a month to control for repeated retrieval. Memory for gist was higher than for peripheral details, which were forgotten at a faster rate over a month, with or without the presence of intermediate recall. Moreover, repeated retrieval had a significant benefit on both memory for gist and peripheral details. We conclude that the different nature of gist and peripheral details leads to a differential forgetting in prose free recall, while repeated retrieval does not have a differential effect on the retention of these different episodic details.

Detecting accelerated long-term forgetting: A problem and some solutions

While many memory disorders occur with normal rates of forgetting, an accelerated rate of long-term forgetting (ALF) may occur, sometimes in the absence of a learning deficit. Detecting ALF presents a problem as it is desirable that the learned material is re-tested after each of several delays. This may result in earlier retrievals confounding later tests, with evidence suggesting that both positive and negative interaction can occur between successive tests. An earlier study (Baddeley et al., 2019) tested cued recall of a series of four crimes or four visual scenes by probing a different sample of features from all four crimes/scenes at each delay. Even though no question was asked twice, the interpolated tests markedly reduced the rate of forgetting. We suggest that this decelerated forgetting effect may result from the retrieval of probed features activating other associated features within that episode, hence facilitating their recall on subsequent tests. If so, the effect should be removed when only single and separate episodes, or individual items, are tested at each delay. We test this by probing a separate episode at each delay (Experiment 1), or by replacing integrated episodes with recognition memory for isolated words (Experiments 2 and 3) or visual scenes (Experiments 4 and 5). As predicted, we find no reduction in the rate of forgetting, in contrast to our earlier studies. The theoretical and clinical implications of our results are discussed. We conclude that the previously developed Crimes and Four Doors Tests (Baddeley et al., 2019) and the present single item recognition tests are complementary and are both likely to be necessary to ensure the reliable detection of ALF.

The use of novel measures to detect Accelerated Long-term forgetting in people with epilepsy: The Crimes Test and Four Doors Test

Most patients with memory disorders appear to forget at a relatively normal rate. Hence testing retention beyond the initial test session becomes unnecessary. However, it is now well established that a subsample of patients, most notably people with epilepsy, can show substantially increased forgetting rates even when acquisition rate is normal, raising the need for new tests focused on the assessment of long-term forgetting. Our study is part of the process of developing two such tests. Both focus on the need to test the same person several times and address the problem that each successive test may interfere with the memory of the event being tested. Depending on conditions, such effects can be substantial and may be either positive or negative. The Crimes and Four Doors Tests tackle this problem by presenting easily memorised episodes or scenes, from which a different sample of features is tested at each delay by telephone. We apply these two novel tests to assess rates of forgetting in groups of people with epilepsy and a matched control group. Both the visual and verbal tests showed clear evidence of accelerated forgetting in the epilepsy group supporting the potential value of the tests as convenient and sensitive measures of the rate of long-term forgetting.