Neural Patterns in Linguistic Cortices Discriminate the Content of Verbal Working Memory.

An influential theoretical account of working memory (WM) considers that WM is based on direct activation of long-term memory knowledge. While there is empirical support for this position in the visual WM domain, direct evidence is scarce in the verbal WM domain. This question is critical for models of verbal WM, as the question of whether short-term maintenance of verbal information relies on direct activation within the long-term linguistic knowledge base or not is still debated. In this study, we examined the extent to which short-term maintenance of lexico-semantic knowledge relies on neural activation patterns in linguistic cortices, and this by using a fast encoding running span task for word and nonword stimuli minimizing strategic encoding mechanisms. Multivariate analyses showed specific neural patterns for the encoding and maintenance of word versus nonword stimuli. These patterns were not detectable anymore when participants were instructed to stop maintaining the memoranda. The patterns involved specific regions within the dorsal and ventral pathways, which are considered to support phonological and semantic processing to various degrees. This study provides novel evidence for a role of linguistic cortices in the representation of long-term memory linguistic knowledge during WM processing.

Verbal working memory and linguistic long-term memory: Exploring the lexical cohort effect.

Numerous studies have shown that verbal working memory (vWM) performance is strongly influenced by linguistic knowledge, with items more familiar at sublexical, lexical, and/or semantic levels leading to higher vWM recall performance. Among the many different psycholinguistic variables whose impact on vWM has been studied, the lexical cohort effect is one of the few effects that has not yet been explored. The lexical cohort effect reflects the fact that words sharing their first phonemes with many other words (e.g. alcove, alligator, alcohol…) are typically responded to more slowly as compared to words sharing their first phonemes with a smaller number of words. In a pilot experiment (Experiment 1), we manipulated the lexical cohort effect in an immediate serial recall task and found no effect. Experiment 2 showed that, in a lexical decision task, participants responded more quickly to items stemming from small cohorts, showing that the material used in Experiment 1 allowed for a valid manipulation of the cohort effect. Experiment 3, using stimuli from Experiment 2 associated with maximal cohort effects during lexical decision, failed again to reveal a cohort effect in an immediate serial recall task. We argue that linguistic knowledge impacts vWM performance via continuous interactive activation within the linguistic system, which is not the case for the lexical cohort variable that may influence language processing only at the initial stages of stimulus activation.

Testing the redintegration hypothesis by a single probe recognition paradigm.

The lexicality effect in verbal short-term memory (STM), in which word lists are better recalled than nonwords lists, is considered to reflect the influence of linguistic long-term memory (LTM) knowledge on verbal STM performance. The locus of this effect remains, however, a matter of debate. The redintegrative account considers that degrading phonological traces of memoranda are reconstructed at recall by selecting lexical LTM representations that match the phonological traces. According to a strong version of this account, redintegrative processes should be strongly reduced in recognition paradigms, leading to reduced LTM effects. We tested this prediction by contrasting word and nonword memoranda in a fast encoding probe recognition paradigm. We observed a very strong lexicality effect, with better and faster recognition performance for words as compared to nonwords. These results do not support a strong version of the redintegrative account of LTM effects in STM which considers that these LTM effects would be the exclusive product of reconstruction mechanisms. If redintegration processes intervene in STM recognition tasks, they must be very fast, which at the same time provides support for models considering direct activation of lexico-semantic knowledge during verbal STM tasks.

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).

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).

Between-item similarity frees up working memory resources through compression: A domain-general property.

Compression, the ability to recode information in a denser format, is a core property of working memory (WM). Previous studies have shown that the ability to compress information largely benefits WM performance. Importantly, recent evidence also suggests compression as freeing up WM resources, thus enhancing recall performance for other, less compressible information. Contrary to the traditional view positing that between-item similarity decreases WM performance, this study shows that between-item similarity can be used to free up WM resources through compression. Across a series of four experiments, we show that between-item similarity not only enhances recall performance for similar items themselves, but also for other, less compressible items within the same list, and this in the semantic (Experiment 1), phonological (Experiment 2), visuospatial (Experiment 3), and visual (Experiment 4) domains. Across these different domains, a consistent pattern of results emerged: between-item similarity proactively-but not retroactively-enhanced WM performance for other items, and this as compared with a condition in which between-item similarity at the whole-list level was minimized. We propose that between-item similarity in any domain may impact WM using the same underlying machinery: via a compression mechanism, which allows an efficient reallocation of WM resources. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Semantic knowledge constrains the processing of serial order information in working memory.

Long-term memory knowledge is considered to impact short-term maintenance of item information in working memory, as opposed to short-term maintenance of serial order information. Evidence supporting an impact of semantic knowledge on serial order maintenance remains weak. In the present study, we demonstrate that semantic knowledge can impact the processing of serial order information in a robust manner. Experiment 1 manipulated semantic relatedness effect by using semantic categories presented in subgroups of items (leaf-tree-branch-cloud-sky-rain). This semantic grouping manipulation was compared to a temporal grouping manipulation whose impact on the processing of serial order information is well-established. Both the semantic and temporal grouping manipulations constrained the occurrence of serial order errors in a robust manner: when migrating to a nontarget serial position, items tended to do so most of the time toward the position of a semantically related item or within the same temporal group. Critically, this impact of semantic knowledge on the pattern of migration errors was not observed anymore in Experiment 2, in which we broke-up the semantic groups, by presenting the semantically related items an interleaved fashion (leaf-cloud-tree-sky-branch-rain). Both semantic and temporal grouping factors may reflect a general mechanism through which information is represented hierarchically. Alternatively, both factors could result from the syntactic and/or semantic regularities that naturally structures linguistic information. These results support models considering direct interactions between serial order and linguistic components of WM. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Can activated long-term memory maintain serial order information?

The maintenance of serial order information is a core component of working memory (WM). Many theoretical models assume the existence of specific serial order mechanisms. Those are considered to be independent from the linguistic system supporting maintenance of item information. This is based on studies showing that psycholinguistic factors strongly affect the ability to maintain item information, while leaving order recall relatively unaffected. Recent language-based accounts suggest, however, that the linguistic system could provide mechanisms that are sufficient for serial order maintenance. A strong version of these accounts postulates serial order maintenance as emerging from the pattern of activation occurring in the linguistic system. In the present study, we tested this assumption via a computational modeling approach by implementing a purely activation-based architecture. We tested this architecture against several experiments involving the manipulation of semantic relatedness, a psycholinguistic variable that has been shown to interact with serial order processing in a complex manner. We show that this activation-based architecture struggles to account for interactions between semantic knowledge and serial order processing. This study fails to support activated long-term memory as an exclusive mechanism supporting serial order maintenance.

The varying nature of semantic effects in working memory.

Several studies have demonstrated an influence of semantic knowledge on verbal working memory (WM) performance, such as shown by the observation of semantic relatedness (related vs. unrelated words) and word imageability (high vs. low imageability words) effects in working memory. The present study extends these observations by examining in four experiments the extent to which semantic knowledge can protect WM representations against interference. We assessed immediate serial recall performance for semantically related vs. unrelated word lists and for high vs. low imageability word lists, with memory lists being followed by an interfering task after encoding or not. Results show that semantic relatedness leads to a stronger protective effect against interference than word imageability at the item level. Furthermore, the semantic relatedness had a stronger impact on WM performance than word imageability; this was further supported by a meta-analysis of all relevant studies in the field. These results suggest that inter-item associative semantic knowledge can protect WM content against interference, but less so item-level semantic knowledge. This protective effect may result from between-item recurrent reactivation or from reduced cognitive load via the compression of memoranda into conceptual units, as further supported by a series of computational simulations.

Domain-Generality of Timing-Based Serial Order Processes in Short-Term Memory: New Insights from Musical and Verbal Domains.

Several models in the verbal domain of short-term memory (STM) consider a dissociation between item and order processing. This view is supported by data demonstrating that different types of time-based interference have a greater effect on memory for the order of to-be-remembered items than on memory for the items themselves. The present study investigated the domain-generality of the item versus serial order dissociation by comparing the differential effects of time-based interfering tasks, such as rhythmic interference and articulatory suppression, on item and order processing in verbal and musical STM domains. In Experiment 1, participants had to maintain sequences of verbal or musical information in STM, followed by a probe sequence, this under different conditions of interference (no-interference, rhythmic interference, articulatory suppression). They were required to decide whether all items of the probe list matched those of the memory list (item condition) or whether the order of the items in the probe sequence matched the order in the memory list (order condition). In Experiment 2, participants performed a serial order probe recognition task for verbal and musical sequences ensuring sequential maintenance processes, under no-interference or rhythmic interference conditions. For Experiment 1, serial order recognition was not significantly more impacted by interfering tasks than was item recognition, this for both verbal and musical domains. For Experiment 2, we observed selective interference of the rhythmic interference condition on both musical and verbal order STM tasks. Overall, the results suggest a similar and selective sensitivity to time-based interference for serial order STM in verbal and musical domains, but only when the STM tasks ensure sequential maintenance processes.