Scale-invariant Characteristics of Forgetting: Toward a Unifying Account of Hippocampal Forgetting across Short and Long Timescales

Detecting recollection: Human evaluators can successfully assess the veracity of others' memories

Humans have the highly adaptive ability to learn from others' memories. However, because memories are prone to errors, in order for others' memories to be a valuable source of information, we need to assess their veracity. Previous studies have shown that linguistic information conveyed in self-reported justifications can be used to train a machine-learner to distinguish true from false memories. But can humans also perform this task, and if so, do they do so in the same way the machine-learner does? Participants were presented with justifications corresponding to Hits and False Alarms and were asked to directly assess whether the witness's recognition was correct or incorrect. In addition, participants assessed justifications' recollective qualities: their vividness, specificity, and the degree of confidence they conveyed. Results show that human evaluators can discriminate Hits from False Alarms above chance levels, based on the justifications provided per item. Their performance was on par with the machine learner. Furthermore, through assessment of the perceived recollective qualities of justifications, participants were able to glean more information from the justifications than they used in their own direct decisions and than the machine learner did.

Forgetting of specific and gist visual associative episodic memory representations across time

Associative binding between components of an episode is vulnerable to forgetting across time. We investigated whether these forgetting effects on inter-item associative memory occur only at specific or also at gist levels of representation. In two experiments, young adult participants (n = 90, and 86, respectively) encoded face-scene pairs and were then tested either immediately after encoding or following a 24-hour delay. Tests featured conjoint recognition judgments, in which participants were tasked with discriminating intact pairs from highly similar foils, less similar foils, and completely dissimilar foils. In both experiments, the 24-hour delay resulted in deficits in specific memory for face-scene pairs, as measured using multinomial-processing-tree analyses. In Experiment 1, gist memory was not affected by the 24-hour delay, but when associative memory was strengthened through pair repetition (Experiment 2), deficits in gist memory following a 24-hour delay were observed. Results suggest that specific representations of associations in episodic memory, and under some conditions gist representations, as well, are susceptible to forgetting across time.

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.

Visual short-term memory impairments in presymptomatic familial Alzheimer's disease: A longitudinal observational study

Visual short-term memory (VSTM) deficits including VSTM binding have been associated with Alzheimer's disease (AD) from preclinical to dementia stages, cross-sectionally. Yet, longitudinal investigations are lacking. The objective of this study was to evaluate VSTM function longitudinally and in relation to expected symptom onset in a cohort of familial Alzheimer's disease. Ninety-nine individuals (23 presymptomatic; 9 symptomatic and 67 controls) were included in an extension cross-sectional study and a sub-sample of 48 (23 presymptomatic carriers, 6 symptomatic and 19 controls), attending two to five visits with a median interval of 1.3 years, included in the longitudinal study. Participants completed the “What was where?” relational binding task (which measures memory for object identification, localisation and object-location binding under different conditions of memory load and delay), neuropsychology assessments and genetic testing. Compared to controls, presymptomatic carriers within 8.5 years of estimated symptom onset showed a faster rate of decline in localisation performance in long-delay conditions (4s) and in traditional neuropsychology measures of verbal episodic memory. This study represents the first longitudinal VSTM investigation and shows that changes in memory resolution may be sensitive to tracking cognitive decline in preclinical AD at least as early as changes in the more traditional verbal episodic memory tasks.

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VSTM function was investigated in presymptomatic and symptomatic FAD carriers.

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PMCs showed faster decline in VSTM function (target localisation) than controls.

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Target localisation accuracy decreased with proximity to expected symptom onset.

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“What was where?” may be sensitive to tracking preclinical cognitive decline.