Strategic search from long-term memory: An examination of semantic and autobiographical recall

Emotional and temporal order effects - a comparison between word-cued and important autobiographical memories recall orders

The retrieval mechanisms associated with the recall of autobiographical memories (AMs) may differ according to the cueing method used to elicit AMs. In the present study, we provide a systematic comparison between word-cued and important AMs in terms of two recall order effects, namely a temporal and an emotional order effect. The sample comprised 104 adults aged between 59 and 90 years. On two measurement occasions, participants recalled up to 20 word-cued and 15 important AMs. For each memory, participants provided their age at the time when the event occurred (age-at-event) and rated its emotionality. Order effects were analysed based on multivariate multilevel model with autoregressive effects for emotionality and age-at-event, respectively. Whereas word-cued AMs showed a stronger emotional order effect, important AMs were recalled temporarily ordered. Individuals differed in the extent to which they ordered AMs along a temporal or emotional dimension. These differences could partly be explained by personality traits. For instance, higher scores on neuroticism were associated with a stronger emotional order effect in both memory types. Findings are discussed in terms of the retrieval mechanisms that are involved in the recall of word-cued and important memory recall and how they may be affected by personality.

Evidence for optimal semantic search throughout adulthood

As people age, they learn and store new knowledge in their semantic memory. Despite learning a tremendous amount of information, people can still recall information relevant to the current situation with ease. To accomplish this, the mind must efficiently organize and search a vast store of information. It also must continue to retrieve information effectively despite changes in cognitive mechanisms due to healthy aging, including a general slowing in information processing and a decline in executive functioning. How effectively does the mind of an individual adjust its search to account for changes due to aging? We tested 746 people ages 25 through 69 on a semantic fluency task (free listing animals) and found that, on average, retrieval follows an optimal path through semantic memory. Participants tended to list a sequence of semantically related animals (e.g., lion, tiger, puma) before switching to a semantically unrelated animal (e.g., whale). We found that the timing of these transitions to semantically unrelated animals was remarkably consistent with an optimal strategy for maximizing the overall rate of retrieval (i.e., the number of animals listed per unit time). Age did not affect an individual's deviation from the optimal strategy given their general performance, suggesting that people adapt and continue to search memory optimally throughout their lives. We argue that this result is more likely due to compensating for a general slowing than a decline in executive functioning.

Neural evidence of switch processes during semantic and phonetic foraging in human memory

Humans may retrieve words from memory by exploring and exploiting in "semantic space" similar to how nonhuman animals forage for resources in physical space. This has been studied using the verbal fluency test (VFT), in which participants generate words belonging to a semantic or phonetic category in a limited time. People produce bursts of related items during VFT, referred to as "clustering" and "switching." The strategic foraging model posits that cognitive search behavior is guided by a monitoring process which detects relevant declines in performance and then triggers the searcher to seek a new patch or cluster in memory after the current patch has been depleted. An alternative body of research proposes that this behavior can be explained by an undirected rather than strategic search process, such as random walks with or without random jumps to new parts of semantic space. This study contributes to this theoretical debate by testing for neural evidence of strategically timed switches during memory search. Thirty participants performed category and letter VFT during functional MRI. Responses were classified as cluster or switch events based on computational metrics of similarity and participant evaluations. Results showed greater hippocampal and posterior cerebellar activation during switching than clustering, even while controlling for interresponse times and linguistic distance. Furthermore, these regions exhibited ramping activity which increased during within-patch search leading up to switches. Findings support the strategic foraging model, clarifying how neural switch processes may guide memory search in a manner akin to foraging in patchy spatial environments.

Lower memory specificity in individuals with dysphoria is not specific to autobiographical memory

BACKGROUND

A core cognitive attribute of depression is lower specificity in the expression of autobiographical memories. Despite interventions targeting memory specificity in depression, its underlying mechanisms are not yet fully understood. Depression also relates to poorer memory for episodic details; here we examine whether reduced specificity might simply reflect broader episodic memory deficits and weakened memory traces with the passage of time.

METHODS

Undergraduate students with and without symptoms of depression completed the Autobiographical Interview and prose-reading episodic memory tasks to assess both same-day and delayed memory.

RESULTS

Dysphoria and nondysphoria groups performed similarly on the tasks of immediate episodic and autobiographical memory; notably, the dysphoria group did not display evidence of lower specificity at this time point. After a delay, however, both groups demonstrated less specific memory responses on both memory tasks, and these declines were more pronounced in the group with dysphoria. That is, after a delay, individuals high in dysphoria showed a greater decrease in the quantity of specific event details reported on both the episodic and the autobiographical memory task. Additional analyses incorporating other clinical and cognitive measures indicated that these relations are largely unique to symptoms of depression.

LIMITATIONS

The sample comprised mostly female students; the study should be replicated with more diverse samples.

CONCLUSIONS

These findings support the claim that lower memory specificity is not peculiar to autobiographical memory, but rather, reflects impoverished memory more generally. This is an important consideration for theories and remedial strategies targeting memory specificity.

Output order effects in autobiographical memory in old age: further evidence for an emotional organisation

It is generally accepted that autobiographical memories (AMs) are organised in associative networks. While both thematic and temporal similarity have been examined as connections among AMs, in the present study we focused on both the positive and negative emotional intensity of events as a possible link among AMs. To do so, we investigated whether the output order with which AMs elicited by cue words were reported can be accounted for emotional intensity of adjacent AMs. Data come from 94 older adults (M [Formula: see text] 67.14; SD [Formula: see text] 6.17) who reported 30 AMs in response to neutral cue words. Positive and negative emotional intensity of AMs were assessed on two separate scales (happiness and sadness). The output order was modeled based on a dual mixed-effects autoregressive model, where the strength of the autoregressive effect indicates how much the emotional intensity of an AM can be predicted by the emotional intensity of the previously reported AM. Results show that there were significant autoregressive effects for both the happiness and sadness ratings (accounting for 4% of variance). We also observed cross-over effects, such that the happiness rating of an AM was predicted by the sadness rating of the previously reported AM (and vice versa). Moreover, we found individual differences in the strength of the autoregressive effects. For the sadness ratings, these individual differences tended to be related to the participant's mood state, particularly so during the first output positions. Together, these findings demonstrate that there is a substantive effect of emotional intensity on the output order with which AMs are reported-even when elicited by cue words. Based on the premise that the output order of AMs informs about the organisation of autobiographical memory, our results highlight the role of emotional associations among AMs in old age.

The role of hippocampus in the retrieval of autobiographical memories in patients with amnestic Mild Cognitive Impairment due to Alzheimer's disease

The role of the hippocampus and neocortical areas in the retrieval of past memories in pre-dementia Alzheimer's disease (AD) patients was investigated. The aim was to assess whether the hippocampus has a temporary role in memory trace formation, according to the Cortical Reallocation Theory (CRT), or whether it continuously updates and enriches memories, according to the Multiple Trace Theory. According to the former theory, hippocampal damage should affect more recent memories, whereas the association cortex is expected to affect memories of the entire lifespan. In the second case, damage to either the hippocampus or the association cortices should affect memories of the entire lifespan. Seventeen patients with amnestic Mild Cognitive Impairment due to AD were submitted to autobiographical (i.e., episodic and semantic personal) memory assessment. Patients underwent MRI for the acquisition of T1-weighted brain volumes. Voxel-based morphometry was used to assess correlations between grey matter (GM) volumes and autobiographical memory. Correlation analyses revealed a strict association between GM volumes in the hippocampus and patients' ability to retrieve the most recent but not the oldest autobiographical memories in both aspects, episodic and semantic. Moreover, patients' GM volumes in the pre-frontal and temporal polar areas were associated with recollection of episodic and semantic events, respectively. Finally, GM volumes in the precuneus and occipital cortex were associated with retrieval of the most recent episodic events. These findings indicate that the hippocampus has a specific time-dependent role; thus, they support the CRT.

Phrase frequency effects in free recall: Evidence for redintegration

Four experiments examined the effects of word and phrase frequency on free recall. Word frequency did not affect word recall, but when participants studied and recalled lists of compositional adjective-noun phrases (e.g. alcoholic beverages), phrase frequency had a consistently beneficial effect: both words from frequent phrases were more likely to be recalled than for infrequent phrases, providing evidence that long-term memory for phrases can aid in pattern completion, or redintegration. We explain these results and those of a previous study of phrase frequency effects in recognition memory (Jacobs et al., 2016) by assuming that the language processing system provides features that are linked to episodic contexts. Recall tasks map from these contexts to linguistic elements, and recognition maps from linguistic elements to contexts. Word and phrase frequency effects in both memory tasks emerge both within the language processing system and from multiple stored episodes, and the fact that the representations of phrases are tied to knowledge of their component words, rather than being representational islands.

Semantic search during divergent thinking

Divergent thinking, as a method of examining creative cognition, has not been adequately analyzed in the context of modern cognitive theories. This article casts divergent thinking responding in the context of theories of memory search. First, it was argued that divergent thinking tasks are similar to semantic fluency tasks, but are more constrained, and less well structured. Next, response time distributions from 54 participants were analyzed for temporal and semantic clustering. Participants responded to two prompts from the alternative uses test: uses for a brick and uses for a bottle, for two minutes each. Participants' cumulative response curves were negatively accelerating, in line with theories of search of associative memory. However, results of analyses of semantic and temporal clustering suggested that clustering is less evident in alternative uses responding compared to semantic fluency tasks. This suggests either that divergent thinking responding does not involve an exhaustive search through a clustered memory trace, but rather that the process is more exploratory, yielding fewer overall responses that tend to drift away from close associates of the divergent thinking prompt.