The episodic nature of episodic-like memories

Studying episodic memory in nonhuman animals has proved difficult because definitions in humans require conscious recollection. Here, we assessed humans' experience of episodic-like recognition memory tasks that have been used with animals. It was found that tasks using contextual information to discriminate events could only be accurately performed using recollection, not familiarity. However, tasks using temporal information to discriminate events could be accurately performed using either recollection or familiarity. The results strengthen the position that some episodic-like recognition memory tasks are a valid model of episodic memory. However, tasks that rely on temporal information may be susceptible to nonepisodic strategies.     

Aging memories: differential decay of episodic memory components

Some memories about events can persist for decades, even a lifetime. However, recent memories incorporate rich sensory information, including knowledge on the spatial and temporal ordering of event features, while old memories typically lack this "filmic" quality. We suggest that this apparent change in the nature of memories may reflect a preferential loss of hippocampus-dependent, configurational information over more cortically based memory components, including memory for individual objects. The current study systematically tests this hypothesis, using a new paradigm that allows the contemporaneous assessment of memory for objects, object pairings, and object-position conjunctions. Retention of each memory component was tested, at multiple intervals, up to 3 mo following encoding. The three memory subtasks adopted the same retrieval paradigm and were matched for initial difficulty. Results show differential decay of the tested episodic memory components, whereby memory for configurational aspects of a scene (objects' co-occurrence and object position) decays faster than memory for featured objects. Interestingly, memory requiring a visually detailed object representation decays at a similar rate as global object recognition, arguing against interpretations based on task difficulty and against the notion that (visual) detail is forgotten preferentially. These findings show that memories undergo qualitative changes as they age. More specifically, event memories become less configurational over time, preferentially losing some of the higher order associations that are dependent on the hippocampus for initial fast encoding. Implications for theories of long-term memory are discussed.     

The role of semantic knowledge in retrieval from episodic long-term memories: Implications for a model of retrieval

Two experiments were conducted, using a paired-associate recall reaction time paradigm, to assess the role semantic knowledge plays in retrieval of long-term episodic memories. In Experiment I, word frequency and meaningfulness were manipulated; high-frequency stimuli led to significantly longer reaction times, while meaningfulness had no significant effect. In Experiment II, the role of the distribution of preexperimental associates of the stimulus was further investigated by comparing retrieval time when the stimulus had either a high- or low-strength primary associate; the former resulted in longer reaction times. The implications of these results for a model of retrieval were discussed. Exhaustive search models were found inadequate, but viable parallel and serial self-terminating models were developed. In both of these models, retrieval time is a function of strength of the correct associate, relative to total strength of a restricted set of semantic associates of the stimulus.     

Reconsolidation of episodic memories: a subtle reminder triggers integration of new information

Recent demonstrations of "reconsolidation" suggest that memories can be modified when they are reactivated. Reconsolidation has been observed in human procedural memory and in implicit memory in infants. This study asks whether episodic memory undergoes reconsolidation. College students learned a list of objects on Day 1. On Day 2, they received a reminder or not, and then learned a second list. Memory for List 1 was tested immediately on Day 2 (Experiment 2) or on Day 3 (Experiment 1). Although the reminder did not moderate the number of items recalled from List 1 on either day, subjects who received a reminder incorrectly intermixed items from the second list when recalling List 1 on Day 3. Experiment 2 showed that this effect does not occur immediately and thus is time-dependent. The reminder did not affect memory for List 2 on Day 3 (Experiment 3), demonstrating that modification occurred only for the original memory (List 1). The study demonstrates the crucial role of reminders for the modification of episodic memory, that reconsolidation of episodic memory is time-dependent, and, in contrast to previous reconsolidation findings, that reconsolidation is also a constructive process, one that supports the incorporation of new information in memory.     

The episodic nature of involuntary autobiographical memories

Involuntary autobiographical memories are conscious and unintended recollections of personal experiences. In Study 1, involuntary memories were compared with voluntary word-cued memories, both retrieved in naturalistic settings via a self-paced procedure. The involuntary memories more frequently referred to specific episodes, came with more physical reaction, had more impact on mood, and dealt with more unusual and less positive events. Study 2 demonstrated that these differences were not due to differences between verbal and nonverbal cues, by using Francis Galton's "memory walk" as a nonverbal method to cue voluntary memories. In both studies, systematic differences were found between specific and nonspecific memories. The findings show that the way autobiographical memories are sampled greatly affects the findings and that involuntary retrieval more often provides access to memories of specific episodes and associated emotional states.     

Perceptual priming enhances the creation of new episodic memories

In recent years, most studies of human memory systems have placed the emphasis on differences rather than on similarities. The present study sought to assess the impact of perceptual priming on the creation of new episodic memories. It was composed of three distinct experimental phases: (1) an initial study phase, during which the number of repetitions of target words was manipulated; (2) a perceptual priming test phase, involving both target and new control words, which constituted the incidental encoding phase of (3) a subsequent Remember/Know/Guess recognition task. Results showed that the greater the perceptual priming at encoding, the more the episodic memory performance was enhanced, whereas no such relation was found for know judgments or feeling of familiarity. Furthermore, the words that were associated with the creation of new episodic memories had been perceptually primed to a greater extent during the incidental encoding phase than the words that were subsequently judged to be known or forgotten. These results suggest that the perceptual contents of episodic memories are constituted by the very perceptual representations that generate priming effects. Potential mechanisms linking perceptual priming to the creation of episodic memories are discussed.     

More on the distinction between episodic and semantic memories

In reply to a critique of the episodic/semantic distinction (McKoon, Ratcliff, & Dell, 1986), Tulving (1986) argues that the usual rules for testing theories do not apply to the classification of phenomena with respect to memory systems. But we respond that the classification methods proposed by Tulving (1986) may be detrimental to the advancement of theory and that whole domains of inquiry should not be excluded from the usual criteria of experimental psychology.     

The role of lifetime periods in the organisation of episodic memories

ABSTRACT

Research on the nature of episodic memory associations has suggested that episodic memories are associated by conceptual knowledge, where memories cluster around the same content (e.g. memories about the same people) or general-event knowledge, where memories cluster around extended events (e.g. a holiday in London), repeated events (e.g. Sunday walks in the park), or causally related events (i.e. where one event leads to another). Research has also suggested that episodic memories are associated by lifetime periods (e.g. when I was in high school), where memories cluster within lifetime periods. However, it is unclear whether episodic memories can be associated solely by lifetime periods, or if such associations are subordinate to conceptual or general-event associations. To answer this question, we reanalysed a large sample of involuntary memory chains (Mace, J. H., Clevinger, A. M., & Bernas, R. S. (2013). Involuntary memory chains: What do they tell us about autobiographical memory organisation? Memory, 21, 324–335). The results of this analysis suggested that lifetime periods associations are subordinate to conceptual and general-event associations, as lifetime periods were found to cluster within the latter two associations. The potential functions of this organisation are discussed.     

The role of episodic memories in current and future well-being

The purpose of the present research was to examine the automatic role of psychological need satisfaction in episodic memories and in their associated networked memories on people's sense of well-being. In each of four studies, participants were asked to describe a main episodic memory and networked memories, that is, other memories related to their main episodic memory. Results of Studies 1 and 2 revealed that levels of need satisfaction in a main episodic memory and in its networked memories both uniquely contributed to the prediction of well-being (based on either participants' or peers' ratings). Study 3 examined the automatic effect of priming an episodic memory network on people's well-being in the here and now. Study 4 revealed that need satisfaction in episodic memory networks predicted changes in well-being over time. In addition, this relationship held after controlling for broad dispositional traits, mental health, and general need satisfaction ratings.     

Computational models of the hippocampal region: linking incremental learning and episodic memory

The hippocampal region, a group of brain structures important for learning and memory, has been the focus of a large number of computational models. These tend to fall into two groups: (1) models of the role of the hippocampal region in incremental learning, which focus on the development of new representations that are sensitive to stimulus regularities and environmental context; (2) models that focus on the role of the hippocampal region in the rapid storage and retrieval of episodic memories. Rather than being in conflict, it is becoming apparent that both approaches are partially correct and might reflect the different functions of substructures of the hippocampal region. Future computational models will help to elaborate how these different substructures interact.     

Integrating episodic memories and prior knowledge at multiple levels of abstraction

Prior knowledge can have a large influence on recall when the memory for the original event is error prone or incomplete. We investigated the interaction between memory and prior knowledge in a recall task involving natural objects such as fruits and vegetables. We first quantified prior knowledge for the sizes of objects in a norming experiment. We then assessed the influence of prior knowledge in a memory experiment in which we compared the actual size of objects shown during a study phase with the reconstructed size of an object during the test phase. Recall was biased both by the mean size of the specific object studied and by the mean size of all objects in the category. This result suggests that the influence of prior knowledge can come from multiple, hierarchically related levels of representation, such as the object-category and superordinate-category levels.     

Failures to find suppression of episodic memories in the think/no-think paradigm

Anderson and Green (2001) had subjects learn paired associates and then selectively suppress responses to some of them. They reported a decrease in final cued recall for responses that subjectshad been instructed not to think of and explained their data as resulting from cognitive suppression, a laboratory analog of repression. We report three experiments designed to replicate the suppression/repression results. After subjects learned a series of A-B word pairs (e.g., ordsea-roach), they were then asked to respond to some items and not to think of other items when shown their cues 1, 8, or 16times. During a final recall test, they were cued with either asame (direct)probe (ordeal-__) or a n independent(indirect) probe (insect-r__) . None of our experiments showed reliable suppression effects with either the same or independent-probe tests. Suppression is apparently not a robust experimental phenomenon in the think/no-think paradigm.     

Validation of a rodent model of episodic memory

Episodic memory consists of representations of specific episodes that happened in the past. Modeling episodic memory in animals requires careful examination of alternative explanations of performance. Putative evidence of episodic-like memory may be based on encoding failure or expectations derived from well-learned semantic rules. In Experiment 1, rats were tested in a radial maze with study and test phases separated by a retention interval. The replenishment of chocolate (at its study-phase location) depended on two factors: time of day (morning vs. afternoon) and the presence or absence of chocolate pellets at the start of the test phase. Because replenishment could not be decoded until the test phase, rats were required to encode the study episode. Success in this task rules out encoding failure. In Experiment 2, two identical mazes in different rooms were used. Chocolate replenishment was trained in one room, and then they were asked to report about a recent event in a different room, where they had no expectation that the memory assessment would occur. Rats successfully answered the unexpected question, ruling out use of expectations derived from well-learned semantic rules. Our behavioral methods for modeling episodic memory may have broad application for assessments of genetic, neuroanatomical, neurochemical, and neurophysiological bases of both episodic memory and memory disorders such as those that occur in Alzheimer’s disease.     

Integrating incremental learning and episodic memory models of the hippocampal region

By integrating previous computational models of corticohippocampal function, the authors develop and test a unified theory of the neural substrates of familiarity, recollection, and classical conditioning. This approach integrates models from 2 traditions of hippocampal modeling, those of episodic memory and incremental learning, by drawing on an earlier mathematical model of conditioning, SOP (A. Wagner, 1981). The model describes how a familiarity signal may arise from parahippocampal cortices, giving a novel explanation for the finding that the neural response to a stimulus in these regions decreases with increasing stimulus familiarity. Recollection is ascribed to the hippocampus proper. It is shown how the properties of episodic representations in the neocortex, parahippocampal gyrus, and hippocampus proper may explain phenomena in classical conditioning. The model reproduces the effects of hippocampal, septal, and broad hippocampal region lesions on contextual modulation of classical conditioning, blocking, learned irrelevance, and latent inhibition.     

Looking at the past through a telescope: adults postdated their earliest childhood memories

ABSTRACT

Our previous studies have consistently shown a telescoping error in children’s dating of earliest childhood memories. Preschool children through adolescents systematically date their earliest memories at older ages, in comparison with the age estimates provided by their parents or by themselves previously. In the current study, we examined the dating of earliest childhood memories in two samples of college adults and collected independent age estimates from their parents. Consistent with our findings with children, adults significantly postdated their earlier memories by approximately 12 months (Study 1) and 6 months (Study 2). The actual age of earliest memories was 2.5 years after adjusted for telescoping errors, 1 year earlier than what is commonly believed at 3.5 years. These findings challenge commonly held theoretical assumptions about childhood amnesia and highlight critical methodological issues in the study of childhood memory.     

Improved episodic integration through enactment: implications for aging

Enactment may improve memory for verb phrases by facilitating episodic integration of object-action components into a unitized whole. It is unclear, however, whether the influence of enactment on episodic integration is related to or independent of the strength of the preexisting semantic relationship between components. To address this issue, the authors examined the influence of enactment on memory for lists of semantically related object-action phrases ("Put money in the wallet") and semantically unrelated phrases created by repairing these objects and actions to make phrases that were unusual but still were possible to perform ("String a thread through the wallet," "Put money in the napkin"). As such, phrases in the related and unrelated lists were matched for familiarity of the individual components and differed only in the associative strength of the object-action relationship. Although verbatim recall of unrelated lists was poorer under standard verbal encoding conditions, enactment succeeded in bringing performance to the level of related lists, indicating that enactment's influence on episodic integration was independent of the semantic relatedness of the object and action components. Analysis of partial recall errors (accurate recall of only one component) suggested that enactment benefited recall in the unrelated lists by improving memory for the action and reducing fragmentation of the association, providing further support for the unitization view. This pattern of results was replicated in normal older adults, a population that exhibits particular difficulty with episodic memory for unrelated associations. The cognitive mechanisms by which enactment may improve episodic integration in both younger and older adults are discussed.