The benefits of memory control processes in working memory: Comparing effects of self-reported and instructed strategy use.

Working memory performance is often assumed to benefit from different maintenance control strategies such as rehearsal, refreshing, elaboration, and grouping. In studies assessing strategy self-reports, some strategies were indeed associated with better recall. Nevertheless, experimental studies assessing the effect of instructing maintenance strategies compared to a no-instruction baseline lend no evidence for the effectiveness of these strategies for working memory. Explanations for this contradiction could be that instruction implementation engenders dual-task costs or that strategy instructions reduce adaptive strategy switching. Across two experiments, we investigated the frequency and variability of strategy use with trial-wise self-reports in serial recall of word lists. Furthermore, we examined potential instruction costs by comparing performance in trials with self-reported versus instructed use of the same strategies. Self-reported strategy use varied from trial to trial, with elaboration and rehearsal being the most frequent. Self-reported elaboration was correlated with better performance than reading and rehearsal. For the most prevalent strategies-elaboration and rehearsal-there were no costs of instructed strategy implementation. Our results speak against dual-task costs and for the advantage of adaptively choosing one's own strategy from trial to trial. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Testing the response suppression mechanism of working memory.

Many working memory (WM) paradigms involve recalling multiple items from the same memory set. Participants rarely repeat items they have already recalled, avoiding repetition errors. To prevent these errors, WM models incorporate a response suppression mechanism that removes recalled items from the set of response options. Despite its importance for our understanding of WM, response suppression has received limited direct testing. To address this gap, we used computational models implementing two hypothetical mechanisms of response suppression to derive predictions and tested these predictions experimentally. Participants were asked to recall the same items multiple times during a single trial. If already recalled items are removed from the response set to prevent repetition errors, memory performance should be impaired when the same item is tested again. Contrary to this, we found that memory performance was unimpaired when the same item was tested a second time, and even displayed a recall advantage. Therefore, this study demonstrates the implausibility of response suppression to account for how people avoid repetition errors. We discuss alternative explanations. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Grouping in working memory guides chunk formation in long-term memory: Evidence from the Hebb effect.

The Hebb effect refers to the improvement in immediate memory performance on a repeated list compared to unrepeated lists. That is, participants create a long-term memory representation over repetitions, on which they can draw in working memory tests. These long-term memory representations are likely formed by chunk acquisition: The whole list becomes integrated into a single unified representation. Previous research suggests that the formation of such chunks is rather inflexible and only occurs when at least the beginning of the list repeats across trials. However, recent work has shown that repetition learning strongly depends on participants recognizing the repeated information. Hence, successful chunk formation may depend on the recognizability of the repeated part of a list, and not on its position in the list. Across six experiments, we compared these two alternatives. We tested immediate serial recall of eight-letter lists, some of which partially repeated across trials. We used different partial-repetition structures, such as repeating only the first half of a list, or only every second item. We manipulated the salience of the repeating structure by spatially grouping and coloring the lists according to the repetition structure. We found that chunk formation is more flexible than previously assumed: Participants learned contiguous repeated sequences regardless of their position within the list, as long as they were able to recognize the repeated structure. Even when the repeated sequence occurred at varying positions over repetitions, learning was preserved when the repeated sequence was made salient by the spatial grouping. These findings suggest that chunk formation requires recognition of which items constitute a repeating group, and demonstrate a close link between grouping of information in working memory, and chunk formation in long-term memory.

Does semantic similarity affect immediate memory for order? Usually not, but sometimes it does.

Recall performance in working memory (WM) is strongly affected by the similarity between items. When asked to encode and recall list of items in their serial order, people confuse more often the position of similar compared to dissimilar items. Models of WM explain this deleterious effect of similarity through a problem of discriminability between WM representations. In contrast, when lists of items that are all semantically similar are compared to lists of dissimilar items, semantic similarity does not negatively impact order memory, questioning the idea that semantic information is part of the WM content. This study reports four experiments in which semantic similarity was manipulated using lists composed of multiple semantic categories. These experiments revealed two main patterns. First, semantic similarity can increase, rather than decrease, order memory. Second, semantic knowledge reliably constrains the way items migrate; when migrating, items tend to do so more often toward the position of other similar items, rather than migrating toward other dissimilar items. These results challenge the way current models of WM represent similarity. The plausibility of different theoretical accounts and mechanisms is discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Testing expectations and retrieval practice modulate repetition learning of visuospatial arrays.

One of the best-known demonstrations of long-term learning through repetition is the Hebb effect: Immediate recall of a memory list repeated amidst nonrepeated lists improves steadily with repetitions. However, previous studies often failed to observe this effect for visuospatial arrays. Souza and Oberauer (2022) showed that the strongest determinant for producing learning was the difficulty of the test: Learning was consistently observed when participants recalled all items of a visuospatial array (difficult test) but not if only one item was recalled, or recognition procedures were used (less difficult tests). This suggests that long-term learning was promoted by increased testing demands over the short term. Alternatively, it is possible that lower testing demands still lead to learning but prevented the application of what was learned. In four preregistered experiments (N = 981), we ruled out this alternative explanation: Changing the type of memory test midway through the experiment from less demanding (i.e., single item recall or recognition) to a more demanding test (i.e., full item recall) did not reveal hidden learning, and changing it from the more demanding to a less demanding test did not conceal learning. Mixing high and low demanding tests for nonrepeated arrays, however, eventually produced Hebb learning even for the less demanding testing conditions. We propose that testing affects long-term learning in two ways: Expectations of the test difficulty influence how information is encoded into memory, and retrieval consolidates this information in memory. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Hebb repetition effects in complex and simple span tasks are based on the same learning mechanism.

The Hebb repetition effect shows improvement in serial recall of repeated lists compared to random nonrepeated lists. Previous research using simple span tasks found that the Hebb repetition effect is limited to constant uninterrupted lists, suggesting chunking as the mechanism of list learning. However, the Hebb repetition effect has been found in complex span tasks, which challenges the chunking explanation, as successive list items are separated by distractor processing, possibly interfering with the unified representations. We tested the possibility that Hebb repetition learning arises from chunking in simple span, but from position-item associations in complex span. In a series of five experiments, we found evidence that contradicts that hypothesis. Results show that (a) Hebb repetition learning in a complex span task can be transferred to a simple span task; (b) Hebb repetition learning from a complex span task cannot be transferred to a partially repeated simple span task; (c) partial repetition in a complex span task does not lead to learning; (d) Hebb repetition learning from a simple span task can be transferred to a complex span task; and (e) repeating the distractors in complex span has no impact on the Hebb repetition effect. These results suggest that the mechanism underlying the Hebb repetition effect in simple and complex span tasks is the same and points at the creation of chunks while excluding the distractors from the long-term memory representation. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

An interference model for visual and verbal working memory.

Research on working memory (WM) has followed two largely independent traditions: One concerned with memory for sequentially presented lists of discrete items, and the other with short-term maintenance of simultaneously presented arrays of objects with simple, continuously varying features. Here we present a formal model of WM, the interference model (IM), that explains benchmark findings from both traditions: The shape of the error distribution from continuous reproduction of visual features, and how it is affected by memory set size; the effects of serial position for sequentially presented items, the effect of output position, and the intrusion of nontargets as a function of their distance from the target in space and in time. We apply the model to two experiments combining features of popular paradigms from both traditions: Lists of colors (Experiment 1) or of nonwords (Experiment 2) are presented sequentially and tested through selection of the target from a set of candidates, ordered by their similarity. The core assumptions of the IM are: Contents are encoded into WM through temporary bindings to contexts that serve as retrieval cues to access the contents. Bindings have limited precision on the context and the content dimension. A subset of the memory set-usually one item and its context-is maintained in a focus of attention with high precision. Successive events in an episode are encoded with decreasing strength, generating a primacy gradient. With each encoded event, automatic updating of WM reduces the strength of preceding memories, creating a recency gradient and output interference. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

When Does Episodic Memory Contribute to Performance in Tests of Working Memory?

Both the experimental and the psychometric investigation of the WM capacity limit depend critically on the assumption that performance in our tests of WM reflects that capacity limit to a good approximation. Most tasks to measure WM rely on testing memory after a short time during which participants are asked to maintain information in WM. In these tests, episodic long-term memory is likely to also lay down a trace of the memory set. Therefore, participants can draw on two sources of information when memory is tested, making it difficult to separate the contributions of WM and episodic LTM to the performance on immediate-memory tests. Here we use proactive interference to distinguish between these two sources of remembered information, building on the fact that episodic memory is vulnerable to proactive interference, whereas WM is protected against it. We use a release-from-PI paradigm to determine the extent to which commonly used WM tasks reflect contributions from episodic LTM. We focus on memory for serial order of verbal lists, but also include visual and spatial WM tasks. The results of five experiments demonstrate that although some tasks used to investigate WM are heavily contaminated by episodic LTM, other popular paradigms such as serial and probed recall, and the standard version of the continuous color-reproduction task, are not. Measuring proactive interference can help researchers determine the extent to which WM and episodic LTM contribute to performance in immediate-memory tasks.

Repetition learning is neither a continuous nor an implicit process.

Learning advances through repetition. A classic paradigm for studying this process is the Hebb repetition effect: Immediate serial recall performance improves for lists presented repeatedly as compared to nonrepeated lists. Learning in the Hebb paradigm has been described as a slow but continuous accumulation of long-term memory traces over repetitions [e.g., Page & Norris, Phil. Trans. R. Soc. B 364, 3737-3753 (2009)]. Furthermore, it has been argued that Hebb repetition learning requires no awareness of the repetition, thereby being an instance of implicit learning [e.g., Guérard et al., Mem. Cogn. 39, 1012-1022 (2011); McKelvie,  J. Gen. Psychol. 114, 75-88 (1987)]. While these assumptions match the data from a group-level perspective, another picture emerges when analyzing data on the individual level. We used a Bayesian hierarchical mixture modeling approach to describe individual learning curves. In two preregistered experiments, using a visual and a verbal Hebb repetition task, we demonstrate that 1) individual learning curves show an abrupt onset followed by rapid growth, with a variable time for the onset of learning across individuals, and that 2) learning onset was preceded by, or coincided with, participants becoming aware of the repetition. These results imply that repetition learning is not implicit and that the appearance of a slow and gradual accumulation of knowledge is an artifact of averaging over individual learning curves.

Measurement models for visual working memory-A factorial model comparison.

Several measurement models have been proposed for data from the continuous-reproduction paradigm for studying visual working memory (WM): The original mixture model (Zhang & Luck, 2008) and its extension (Bays et al., 2009); the interference measurement model (IMM; Oberauer et al., 2017), and the target confusability competition (TCC) model (Schurgin et al., 2020). This article describes a space of possible measurement models in which all these models can be placed. The space is defined by three dimensions: (a) The choice of an activation function (von-Mises or Laplace), (b) the choice of a response-selection function (variants of Luce's choice rule or of signal-detection theory), (c) and whether or not memory precision is assumed to be a constant over manipulations affecting memory. A factorial combination of these three variables generates all possible models in the model space. Fitting all models to eight data sets revealed a new model as empirically most adequate, which combines a von-Mises activation function with a signal-detection response-selection rule. The precision parameter can be treated as a constant across many experimental manipulations, though it probably varies between individuals. All modeling code and the raw data modeled are available on the OSF: https://osf.io/zwprv/ (PsycInfo Database Record (c) 2023 APA, all rights reserved).

The contribution of episodic long-term memory to working memory for bindings.

The present experiments support two conclusions about the capacity limit of working memory (WM). First, they provide evidence for the Binding Hypothesis, WM capacity is limited by interference between bindings but not items. Second, they show that episodic LTM contributes substantially to binding memory when the capacity of WM is stretched to the limit by larger set sizes. We tested immediate memory for sets of word-picture pairs. With increasing set size, memory for bindings declined more precipitously than memory for items, as predicted from the binding hypothesis. Yet, at higher set sizes performance was more stable than expected from a capacity limited memory, suggesting a contribution of episodic long-term memory (LTM) to circumvent the WM capacity limit. In support of that hypothesis, we show a double dissociation of contributions of WM and episodic LTM to binding memory: Performance at set sizes larger than 3 was specifically affected by proactive interference - but were immune to influences from a distractor-filled delay. In contrast, performance at set size 2 was unaffected by proactive interference but harmed by a distractor-filled delay.

When do we know that we do not know? An examination of metacognitive processes in visual working memory.

This work investigates how people make judgments about the content of their visual working memory (VWM). Some studies on long-term memory suggest that people base those metacognitive judgments on the outcome of a retrieval attempt. In contrast, Son and Metcalfe (2005) observed that people identify poorly remembered items immediately, presumably by the lack of familiarity for the retrieval cue. We tested these two hypotheses in the context of metacognition in VWM. In three experiments, we investigated participants' response behavior in a color reproduction task with a hidden color wheel. With this procedure, participants must search for the intended response, starting from a random color. We assumed that instant awareness of the inability to retrieve an information would be reflected in selecting the first, random color, rather than search for a particular color in the wheel. Although participants provided a substantial number of low-confidence responses, results of an adapted mixture modeling analysis yielded little evidence for quick guesses. Rather, participants consistently searched for a color (even with unfamiliar retrieval cues in Experiment 2), and only quickly guessed when being cued with objects at test that were not previously presented (Experiment 3). We conclude that people usually engage in retrieval attempts for providing judgments about their VWM, even when information is poorly remembered. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

When does working memory get better with longer time?

Longer free time between presentation of verbal list items often leads to better immediate serial recall. The present series of three experiments demonstrates that this beneficial effect of time is more general than has been known: It is found for verbal items presented visually and auditorily (Experiments 1 and 2), and also when people engage in concurrent articulation during presentation, thereby preventing rehearsal (Experiment 3). The effect of time is to improve memory most strongly for the later part of the list, contrary to what is predicted from the assumption that time between items is used to bolster memory traces of already encoded items through rehearsal, refreshing, or elaboration. The data are compatible with a ballistic form of short-term consolidation, and with the assumption that encoding an item into working memory partially depletes a limited resource, which is replenished over time. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Evidence Against Novelty-Gated Encoding in Serial Recall.

Novelty-gated encoding is the assumption that events are encoded more strongly into memory when they are more novel in comparison to previously encoded events. It is a core assumption of the SOB model of serial recall (Farrell & Lewandowsky, 2002). We present three experiments testing some predictions from novelty-gated encoding. Experiment 1 shows that the probability of recalling the third item in a list correctly does not depend on whether it is preceded by phonologically similar or dissimilar items. Experiment 2 shows that in lists of items from three classes (nonwords, spatial locations, and abstract drawings) the probability of recalling an item does not depend on whether it is preceded by items from the same or another class. Experiment 3 used a complex-span paradigm varying the phonological similarity of words that are read aloud as distractors in between memory items. Contrary to a prediction from novelty-gated encoding, similar distractors did not impair memory more than dissimilar distractors. The results question the assumption of novelty-gated encoding in serial recall. We discuss alternative explanations for the phenomena that this assumption has previously helped to explain. The present evidence against novelty-gated encoding might point to boundary conditions for the role of prediction error in the acquisition of memories.

Is There an Activity-silent Working Memory?

Although storage in working memory (WM) can be tracked via measurements of ongoing neural activity, past work has shown that observers can maintain access to that information despite temporary interruptions of those neural patterns. This observation has been regarded as evidence for a neurally silent form of WM storage. Alternatively, however, unattended information could be retrieved from episodic long-term memory (eLTM) rather than being maintained in WM during the activity-silent period. Here, we tested between these possibilities by examining whether WM performance showed evidence of proactive interference (PI)-a hallmark of retrieval from eLTM-following such interruptions. Participants remembered the colors (Experiments 1-3) or locations (Experiment 4) of serially presented objects. We found PI for set sizes larger than 4, but not for smaller set sizes, suggesting that eLTM may have supported performance when WM capacity was exceeded. Critically, performance with small set sizes remained resistant to PI, even following prolonged interruptions by a challenging distractor task. Thus, we found evidence for PI-resistant memories that were maintained across likely interruptions of storage-related neural activity, an empirical pattern that implies activity-silent storage in WM.

How does visual working memory solve the binding problem?

Location has been highlighted as playing a crucial role in the relationship between memory for features and memory for bindings, with features purportedly bound to one another when they share a location. In three experiments (N = 24, 20, and 24), we show that feature-feature bindings are formed effectively in parallel when stimuli are separated in space but are disrupted when two objects are simultaneously presented in the same location. This pattern holds when conditions are equated with regard to memory for individual features. These findings confirm a prediction from a two-stage model of encoding in visual working memory, in which initial parallel encoding of features in spatial maps is followed by a subsequent sequential binding process that forms object representations that no longer rely on spatial location. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Directed forgetting in working memory.

How does the intent to remember or forget information affect working memory (WM)? To explore this question, in four experiments, we gauged the availability of the to-be-forgotten information directly. Participants remembered six words presented sequentially in separate frames. After each word offset, the frame turned either blue or orange, indicating a to-be-remembered or to-be-forgotten word, respectively. In all experiments, consistently poor recognition performance for to-be-forgotten words and facilitation of to-be-remembered words demonstrated that intent has a strong impact on WM. These directed-forgetting effects are remarkably robust: They can be observed when testing the to-be-forgotten words up to four times (Experiment 1, n = 341), for both item and binding memory (Experiment 3, n = 124), and even when information has to be maintained in WM up to 5 s until the memory cue is presented (Experiment 2 + 4, n = 302 + 321). Our study establishes a new method to jointly study the effects of intent on WM content for both relevant and irrelevant information and provides evidence for directed forgetting in WM. Our research suggests that a combination of two processes causes directed forgetting in WM: One process reduces memory strength of earlier memory representations as a function of subsequently encoded events. Another process rapidly encodes or boosts memory strength only when the person intends to remember that information. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Little Support for Discrete Item Limits in Visual Working Memory.

Some theorists argue that working memory is limited to a discrete number of items and that additional items are not encoded at all. Adam et al. (2017) presented evidence supporting this hypothesis: Participants reproduced visual features of up to six items in a self-chosen order. After the third or fourth response, error distributions were indistinguishable from guessing. I present four experiments with young adults (each N = 24) reexamining this finding. Experiment 1 presented items slowly and sequentially. Experiment 2 presented them simultaneously but longer than in the experiments of Adam et al. Experiments 3 and 4 exactly replicated one original experiment of Adam et al. All four experiments failed to replicate the evidence for guessing-like error distributions. Modeling data from individuals revealed a mixture of some who do and others who do not produce guessing-like distributions. This heterogeneity increases the credibility of an alternative to the item-limit hypothesis: Some individuals decide to guess on hard trials even when they have weak information in memory.

Promoting visual long-term memories: When do we learn from repetitions of visuospatial arrays?

Repeated exposure is assumed to promote long-term learning. This is demonstrated by the so-called "Hebb-effect": when short lists of verbal or spatial materials are presented sequentially for an immediate serial recall test, recall improves with list repetition. This repetition benefit, however, is not ubiquitous. Previous studies found little or no performance improvement for repetitions of visuospatial arrays (e.g., arrays of colored squares). Across eight experiments with college students and Prolific samples, we investigated which factors promote visuospatial learning by testing all combinations of variables distinguishing between visual-array tasks (brief + simultaneous presentation + a single recognition test) and tasks showing the Hebb effect (slow + sequential presentation + recall test probing all items). Participants profited from repetitions when all items were tested with a recall procedure, but not if the test consisted of recognition. Hence, the key to promote long-term learning is to recall all of the memorized information over the short-term. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The Importance of Random Slopes in Mixed Models for Bayesian Hypothesis Testing.

Mixed models are gaining popularity in psychology. For frequentist mixed models, previous research showed that excluding random slopes-differences between individuals in the direction and size of an effect-from a model when they are in the data can lead to a substantial increase in false-positive conclusions in null-hypothesis tests. Here, I demonstrated through five simulations that the same is true for Bayesian hypothesis testing with mixed models, which often yield Bayes factors reflecting very strong evidence for a mean effect on the population level even if there was no such effect. Including random slopes in the model largely eliminates the risk of strong false positives but reduces the chance of obtaining strong evidence for true effects. I recommend starting analysis by testing the support for random slopes in the data and removing them from the models only if there is clear evidence against them.