Pupillary correlates of individual differences in long-term memory

The present study is the first to examine individual differences in long-term memory, arousal dysregulation, and intensity of attention within the same experiment. Participants (N = 106) completed 28 lists of an immediate free recall task while their pupil diameter was recorded via an eye-tracker during the encoding period. Two main pupillary measures were extracted: intraindividual variability in pre-list pupil diameter and evoked pupillary responses during item encoding. Variability in pre-list pupil diameter served as a measure of arousal dysregulation, and evoked pupillary responses served as a measure of intensity of attention. Based on prior work, we hypothesized that there would be a positive association between intensity of attention and recall ability, and that there would be a negative association between arousal dysregulation and recall ability. Collectively these two measures accounted for 19% of interindividual variance in recall, with 5% attributable uniquely to intensity of attention and 12% attributable uniquely to arousal regulation. The findings demonstrate that there are sources of individual differences in long-term memory that can be revealed via pupillometry, notably the amount of effort deployed during item encoding and the degree to which people exhibit dysregulated arousal. Both findings are consistent with recent theorizing regarding the role of the locus coeruleus-norepinephrine (LC-NE) system’s role in goal-directed cognition. Specifically, the LC governs both moment-to-moment arousal and NE release to cortical regions subserving cognitive processing. Among people for whom this system operates most optimally, long-term memory retention is superior.

Does Depth of Processing Affect Temporal Contiguity?

Memory tends to be better when items are processed for their meaning (deep processing) rather than their perceptual features (shallow processing). This levels of processing (LOP) effect is well-replicated and has been applied in many settings, but the mechanisms involved are still not well understood. The temporal contiguity effect (TCE), the finding that recalling one event often triggers recall of another event experienced nearby in time, also predicts memory performance. This effect has given rise to several competing theories with specific contiguity-generating mechanisms related to how items are processed. Therefore, studying how LOP and the TCE interact may shed light on the mechanisms underlying both effects. However, it is unknown how LOP and the TCE interact—the various theories make differing predictions. In this preregistered study, we tested predictions of three theoretical explanations: accounts which assume temporal information is automatically encoded, accounts based on a trade-off between item and order information, and accounts which emphasize the importance of strategic control processes. Participants completed an immediate free recall task where they either engaged in deep processing, shallow processing, or no additional task while studying each word. Recall and the TCE were highest for no-task lists and greater for deep than shallow processing. Our results support theories which assume temporal associations are automatically encoded and those which emphasize strategic control processes. Both perspectives should be considered in theory development. These findings also suggest temporal information may contribute to better recall under deeper processing with implications in determining which situations benefit from deep processing.

Impairment Of Aversive Episodic Memories During COVID-19 Pandemic: The Impact Of Emotional Context On Memory Processes

The threatening context of the COVID-19 pandemic provided a unique setting to study the effects of negative psychological symptoms on memory processes. Episodic memory is an essential function of the human being related to the ability to store and remember experiences and anticipate possible events in the future. Studying this function in this context is crucial to help understand what effects the pandemic will have on the formation of episodic memories. To study this, the formation of episodic memories was evaluated by free recall, recognition, and episode order tasks for an aversive and neutral content. The results indicated that aversive episodic memory is impaired both in the free recall task and in the recognition task. Even the beneficial effect that emotional memory usually has for the episodic order was undermined as there were no differences between the neutral and aversive condition. The present work adds to the evidence that indicates that the level of activation does not modify memory processes in a linear way, which also depends on the type of evocation that people are asked and the characteristics of the content to be encoded.

Recall of Reverberant Speech in Quiet and Four-Talker Babble Noise

Using behavioral evaluation of free recall performance, we investigated whether reverberation and/or noise affected memory performance in normal-hearing adults. Thirty-four participants performed a free-recall task in which they were instructed to repeat the initial word after each sentence and to remember the target words after each list of seven sentences, in a 2 (reverberation) × 2 (noise) factorial design. Pupil dilation responses (baseline and peak pupil dilation) were also recorded sentence-by-sentence while the participants were trying to remember the target words. In noise, speech was presented at an easily audible level using an individualized signal-to-noise ratio (95% speech intelligibility). As expected, recall performance was significantly lower in the noisy environment than in the quiet condition. Regardless of noise interference or reverberation, sentence- baseline values gradually increased with an increase in the number of words to be remembered for a subsequent free-recall task. Long reverberation time had no significant effect on memory retrieval of verbal stimuli or pupillary responses during encoding.

Animate and Inanimate Words Demonstrate Equivalent Retrieval Dynamics Despite the Occurrence of the Animacy Advantage

People demonstrate a memory advantage for animate (living) concepts over inanimate (nonliving) concepts in a variety of memory tasks, including free recall, but we do not know the mechanism(s) that produces this effect. We compared the retrieval dynamics (serial-position effects, probability of first recall, output order, categorical clustering, and recall contiguity) of animate and inanimate words in a typical free recall task to help elucidate this effect. Participants were more likely to recall animate than inanimate words, but we found few, if any, differences in retrieval dynamics by word type. The animacy advantage was obtained across serial position, including occurring in both the primacy and recency regions of the lists. Participants were equally likely to recall an animate or inanimate word first on the tests and did not prioritize recalling words of one type earlier in retrieval or demonstrate strong clustering by animacy at recall. Participants showed some greater contiguity of recall for inanimate words, but this outcome ran counter to the animacy effect. Together, the results suggest that the animacy advantage stems from increased item-specific memory strength for animate over inanimate words and is unlikely to stem from intentional or strategic differences in encoding or retrieval by word type, categorical strategies, or differences in temporal organization. Although the present results do not directly support or refute any current explanations for the animacy advantage, we suggest that measures of retrieval dynamics can help to inspire or constrain future accounts for this effect and can be incorporated into relevant hypothesis testing.

Boundary cells in the representation of episodes in the human hippocampus

The representation of episodes is a fundamental requirement for forming episodic memories, but the specific electrophysiological mechanisms supporting episode construction in the human hippocampus remain unknown. Experiments in rodent models indicate that a population of neurons sensitive to edges of an environment, termed border or boundary neurons in spatial navigation, fulfills a role analogous to episode demarcation. We hypothesized that such boundary neurons could be identified in the human mesial temporal lobe, with firing rates sensitive specifically to the beginning and end of mnemonically-relevant episodes in the free recall task. Using a generalized linear model to control for factors such as encoding success and item onset times along with other variables, we found 44 Boundary neurons out of a total 736 single neurons recorded across 27 subjects. We distinguish boundary neurons from a separate population of ramping neurons, which are time-sensitive neurons whose activity provides complementary but distinct information during episodic representation. We also describe evidence that the firing of boundary neurons within the preferred windows (at the beginning and end of episodes) is organized by hippocampal theta oscillations, using spike-field coherence metrics.

Aging And Emotional Effects On Working Memory And Long-Term Memory For Target And Distracting Information

To resolve discrepancies between studies on the effects of emotional content on working memory, and to examine changes with age, this study examined the effects of emotional content on working memory and subsequent long-term memory for targets and distracters. Thirty-six younger (ages 18-29) and 36 older adults (ages 65-87) participated in a working memory task in which they viewed two target words intermixed with two distracters followed by a probe word, and responded to whether the probe was a target word. The emotional content (valence and arousal) of targets and distracters was manipulated. Subsequent long-term memory was tested with a free recall task. Results indicated that emotional content of targets facilitated working adults experiencing disruption from positive and neutral distracters, and older adults experiencing interference from negative distracters. Emotional effects in long-term memory were only seen for younger adults.

Aging And Emotional Effects On Working Memory And Long-Term Memory For Target And Distracting Information

To resolve discrepancies between studies on the effects of emotional content on working memory, and to examine changes with age, this study examined the effects of emotional content on working memory and subsequent long-term memory for targets and distracters. Thirty-six younger (ages 18-29) and 36 older adults (ages 65-87) participated in a working memory task in which they viewed two target words intermixed with two distracters followed by a probe word, and responded to whether the probe was a target word. The emotional content (valence and arousal) of targets and distracters was manipulated. Subsequent long-term memory was tested with a free recall task. Results indicated that emotional content of targets facilitated working adults experiencing disruption from positive and neutral distracters, and older adults experiencing interference from negative distracters. Emotional effects in long-term memory were only seen for younger adults.

Optimal policies for free recall

There is rich structure in the order in which studied material is recalled in a free recall task (Howard and Kahana, 2002). Extensive effort has been directed at understanding the processes and representations that give rise to this structure; however, it remains unclear why certain types of recall organization might be favored in the first place. We provide a rational analysis of the free recall task, deriving the optimal policy for recalling items under the internal representations and processes described by the Context Maintenance and Retrieval (CMR) model of memory search (Polyn et al.,2009). We show that the optimal policy for free recall is to start from the beginning of the list and then sequentially recall forwards, providing a rational account of the primacy and forward asymmetry effects typically observed in free recall. In addition, when recall is not initiated from the beginning of list, it is optimal during recall transitions to minimize the amount of forward asymmetry. Predictions from the rational model are confirmed in human behavioral data: Top-performing human participants demonstrate a stronger tendency to initiate recall from the beginning of the list and carry forward recalls, and the amount of forward asymmetry in participants depends on whether they start recall from the beginning or end of the list. We discuss the resemblance of the optimal behavior in free recall to participants' behavior when applying mnemonic techniques such as the method of loci.

EFFECT OF WITHIN-ITEM SOCIAL ELABORATION ON INCIDENTAL MEMORY

<p>The present study compared the effects of social and semantic elaboration on incidental memory. Two types of lists were provided to the participants: (1) a related list, in which a triplet of words had a common category name associated with each of them, and (2) an unrelated list, in which the three words did not have a common category name. Then, participants in the social elaboration condition generated a particular person’s name, and those in the semantic elaboration condition generated an association elicited by the three words. An unexpected free recall task followed. Results indicated higher recall of the related list in the social elaboration than in the semantic elaboration condition. In contrast, the unrelated list showed no difference between the two elaboration conditions. These results indicate that social elaboration functions as within-item elaboration, which is more effective than semantic elaboration.</p>