Does Sleep Improve Your Grammar? Preferential Consolidation of Arbitrary Components of New Linguistic Knowledge

Slow Oscillation-Spindle Coupling Predicts Sequence-Based Language Learning

Sentence comprehension involves the decoding of both semantic and grammatical information, a process fundamental to communication. As with other complex cognitive processes, language comprehension relies, in part, on long-term memory. However, the electrophysiological mechanisms underpinning the encoding and generalization of higher-order linguistic knowledge remain elusive, particularly from a sleep-based consolidation perspective. One candidate mechanism that may support the consolidation of higher-order language is the coordination of slow oscillations (SO) and sleep spindles during nonrapid eye movement sleep (NREM). To examine this hypothesis, we analyzed electroencephalographic (EEG) data recorded from 35 participants (M age = 25.4; SD = 7.10; 16 males) during an artificial language learning task, contrasting performance between individuals who were given an 8 h nocturnal sleep period or an equivalent period of wake. We found that sleep relative to wake was associated with superior performance for sequence-based word order rules. Postsleep sequence-based word order processing was further associated with less task-related theta desynchronization, an electrophysiological signature of successful memory consolidation, as well as cognitive control and working memory. Frontal NREM SO-spindle coupling was also positively associated with behavioral sensitivity to sequence-based word order rules, as well as with task-related theta power. As such, theta activity during retrieval of previously learned information correlates with SO-spindle coupling, thus linking neural activity in the sleeping and waking brain. Taken together, this study presents converging behavioral and neurophysiological evidence for a role of NREM SO-spindle coupling and task-related theta activity as signatures of memory consolidation and retrieval in the context of higher-order language learning.

Bilingualism, sleep, and cognition: An integrative view and open research questions

Sleep and language are fundamental to human existence and have both been shown to substantially affect cognitive functioning including memory, attentional performance, and cognitive control. Surprisingly, there is little-to-no research that examines the shared impact of bilingualism and sleep on cognitive functions. In this paper, we provide a general overview of existing research on the interplay between bilingualism and sleep with a specific focus on executive functioning. First, we highlight their interconnections and the resulting implications for cognitive performance. Second, we emphasize the need to explore how bilingualism and sleep intersect at cognitive and neural levels, offering insights into potential ways of studying the interplay between sleep, language learning, and bilingual language use. Finally, we suggest that understanding these relationships could enhance our knowledge of reserve and its role in mitigating age-related cognitive decline.

EPS mid-career prize: An integrated framework for the learning, recognition and interpretation of words

In this article, I review the evidence on the involvement of sleep and consolidation in word learning and processing during language comprehension, focusing on implications for theory. The theoretical basis for the review is a complementary systems account of word learning involving flexible (hippocampal) and stable (cortical) pathways to lexical knowledge. I argue that the accumulated data are consistent with a role for both pathways in both learning and recognition of lexical items, with sleep and consolidation supporting the transfer of recent experience between the pathways. The level of involvement of each pathway is dependent on key factors, such as consistency with prior knowledge in the case of learning, and reliance on context and/or automaticity in the case of recognition. As a consequence, the notion of a mental lexicon cannot really be restricted to just the listener's stable knowledge about words: flexible knowledge and recent experiences are also important. Furthermore, I argue that the flexible pathway plays a critical role even in the absence of new lexical items. The available evidence suggests that this pathway encodes (and potentially consolidates) recent linguistic experiences, providing potential benefits to interpretation of subsequent language and the long-term retention of knowledge. In conclusion, I propose that a dual-pathway account incorporating both flexibility and stability is necessary to explain the learning, recognition, and interpretation of words.

Memory Reactivation during Sleep Does Not Act Holistically on Object Memory

Memory reactivation during sleep is thought to facilitate memory consolidation. Most sleep reactivation research has examined how reactivation of specific facts, objects, and associations benefits their overall retention. However, our memories are not unitary, and not all features of a memory persist in tandem over time. Instead, our memories are transformed, with some features strengthened and others weakened. Does sleep reactivation drive memory transformation? We leveraged the Targeted Memory Reactivation technique in an object category learning paradigm to examine this question. Participants (20 female, 14 male) learned three categories of novel objects, where each object had unique, distinguishing features as well as features shared with other members of its category. We used a real-time EEG protocol to cue the reactivation of these objects during sleep at moments optimized to generate reactivation events. We found that reactivation improved memory for distinguishing features while worsening memory for shared features, suggesting a differentiation process. The results indicate that sleep reactivation does not act holistically on object memories, instead supporting a transformation where some features are enhanced over others.

ENIGMA: A Web Application for Running Online Artificial Grammar Learning Experiments

Artificial grammar learning (AGL) is an experimental paradigm frequently adopted to investigate the unconscious and conscious learning and application of linguistic knowledge. This paper will introduce ENIGMA ( https://enigma-lang.org ) as a free, flexible, and lightweight Web-based tool for running online AGL experiments. The application is optimized for desktop and mobile devices with a user-friendly interface, which can present visual and aural stimuli and elicit judgment responses with RT measures. Without limits in time and space, ENIGMA could help collect more data from participants with diverse personal and language backgrounds and variable cognitive skills. Such data are essential to explain complex factors influencing learners' performance in AGL experiments and answer various research questions regarding L1/L2 acquisition. The introduction of the core features in ENIGMA is followed by an example study that partially replicated Chen (Lang Acquis 27(3):331-361, 2020) to illustrate possible experimental designs and examine the quality of the collected data.

J, Tandoc M, Antony J, Schapiro A. Memory reactivation during sleep does not act holistically on object memory

Memory reactivation during sleep is thought to facilitate memory consolidation. Most sleep reactivation research has examined how reactivation of specific facts, objects, and associations benefits their overall retention. However, our memories are not unitary, and not all features of a memory persist in tandem over time. Instead, our memories are transformed, with some features strengthened and others weakened. Does sleep reactivation drive memory transformation? We leveraged the Targeted Memory Reactivation technique in an object category learning paradigm to examine this question. Participants (20 female, 14 male) learned three categories of novel objects, where each object had unique, distinguishing features as well as features shared with other members of its category. We used a real-time EEG protocol to cue the reactivation of these objects during sleep at moments optimized to generate reactivation events. We found that reactivation improved memory for distinguishing features while worsening memory for shared features, suggesting a differentiation process. The results indicate that sleep reactivation does not act holistically on object memories, instead supporting a transformation process where some features are enhanced over others.

A registered report testing the effect of sleep on Deese-Roediger-McDermott false memory: greater lure and veridical recall but fewer intrusions after sleep

Human memory is known to be supported by sleep. However, less is known about the effect of sleep on false memory, where people incorrectly remember events that never occurred. In the laboratory, false memories are often induced via the Deese-Roediger-McDermott (DRM) paradigm where participants are presented with wordlists comprising semantically related words such as nurse, hospital and sick (studied words). Subsequently, participants are likely to falsely remember that a related lure word such as doctor was presented. Multiple studies have examined whether these false memories are influenced by sleep, with contradictory results. A recent meta-analysis suggests that sleep may increase DRM false memory when short lists are used. We tested this in a registered report (N = 488) with a 2 (Interval: Immediate versus 12 h delay) × 2 (Test Time: 9:00 versus 21:00) between-participant DRM experiment, using short DRM lists (N = 8 words/list) and free recall as the memory test. We found an unexpected time-of-day effect such that completing free recall in the evening led to more intrusions (neither studied nor lure words). Above and beyond this time-of-day effect, the Sleep participants produced fewer intrusions than their Wake counterparts. When this was statistically controlled for, the Sleep participants falsely produced more critical lures. They also correctly recalled more studied words (regardless of intrusions). Exploratory analysis showed that these findings cannot be attributed to differences in output bias, as indexed by the number of total responses. Our overall results cannot be fully captured by existing sleep-specific theories of false memory, but help to define the role of sleep in two more general theories (Fuzzy-Trace and Activation/Monitoring theories) and suggest that sleep may benefit gist abstraction/spreading activation on one hand and memory suppression/source monitoring on the other.

A model of autonomous interactions between hippocampus and neocortex driving sleep-dependent memory consolidation

How do we build up our knowledge of the world over time? Many theories of memory formation and consolidation have posited that the hippocampus stores new information, then "teaches" this information to the neocortex over time, especially during sleep. But it is unclear, mechanistically, how this actually works-How are these systems able to interact during periods with virtually no environmental input to accomplish useful learning and shifts in representation? We provide a framework for thinking about this question, with neural network model simulations serving as demonstrations. The model is composed of hippocampus and neocortical areas, which replay memories and interact with one another completely autonomously during simulated sleep. Oscillations are leveraged to support error-driven learning that leads to useful changes in memory representation and behavior. The model has a non-rapid eye movement (NREM) sleep stage, where dynamics between the hippocampus and neocortex are tightly coupled, with the hippocampus helping neocortex to reinstate high-fidelity versions of new attractors, and a REM sleep stage, where neocortex is able to more freely explore existing attractors. We find that alternating between NREM and REM sleep stages, which alternately focuses the model's replay on recent and remote information, facilitates graceful continual learning. We thus provide an account of how the hippocampus and neocortex can interact without any external input during sleep to drive useful new cortical learning and to protect old knowledge as new information is integrated.

Schematic information influences memory and generalisation behaviour for schema-relevant and -irrelevant information

Schemas modulate memory performance for schema-congruent and -incongruent information. However, it is assumed they do not influence behaviour for information irrelevant to themselves. We assessed memory and generalisation behaviour for information related to an underlying pattern, where a schema could be extracted (schema-relevant), and information that was unrelated and therefore irrelevant to the extracted schema (schema-irrelevant). Using precision measures of long-term memory, where participants learnt associations between words and locations around a circle, we assessed memory and generalisation for schema-relevant and -irrelevant information. Words belonged to two semantic categories: human-made and natural. For one category, word-locations were clustered around one point on the circle (clustered condition), while the other category had word-locations randomly distributed (non-clustered condition). The presence of an underlying pattern in the clustered condition allows for the extraction of a schema that can support both memory and generalisation. At test, participants were presented with old (memory) and new (generalisation) words, requiring them to identify a remembered location or make a best guess. The presence of the clustered pattern modulated memory and generalisation. In the clustered condition, participants placed old and new words in locations consistent with the underlying pattern. In contrast, for the non-clustered condition, participants were less likely to place old and new non-clustered words in locations consistent with the clustered condition. Therefore, we provide evidence that the presence of schematic information modulates memory and generalisation for schema-relevant and -irrelevant information. Our results highlight the need to carefully construct appropriate schema-irrelevant control conditions such that behaviour in these conditions is not modulated by the presence of a schema. Theoretically, models of schema processing need to account for how the presence of schematic information can have consequences for information that is irrelevant to itself.

Effects of Sleep on Language and Motor Consolidation: Evidence of Domain General and Specific Mechanisms

The current study explores the effects of time and sleep on the consolidation of a novel language learning task containing both item-specific knowledge and the extraction of grammatical regularities. We also compare consolidation effects in language and motor sequence learning tasks, to ask whether consolidation mechanisms are domain general. Young adults learned to apply plural inflections to novel words based on morphophonological rules embedded in the input, and learned to type a motor sequence using a keyboard. Participants were randomly assigned into one of two groups, practicing each task during either the morning or evening hours. Both groups were retested 12 and 24 hours post-training. Performance on frequent trained items in the language task stabilized only following sleep, consistent with a hippocampal mechanism for item-specific learning. However, regularity extraction, indicated by generalization to untrained items in the linguistic task, as well as performance on motor sequence learning, improved 24 hours post-training, irrespective of the timing of sleep. This consolidation process is consistent with a frontostriatal skill-learning mechanism, common across the language and motor domains. This conclusion is further reinforced by cross-domain correlations at the individual level between improvement across 24 hours in the motor task and in the low-frequency trained items in the linguistic task, which involve regularity extraction. Taken together, our results at the group and individual levels suggest that some aspects of consolidation are shared across the motor and language domains, and more specifically, between motor sequence learning and grammar learning.

The effect of sleep on novel word learning in healthy adults: A systematic review and meta-analysis

There is increasing evidence to indicate that sleep plays a role in language acquisition and consolidation; however, there has been substantial variability in methodological approaches used to examine this phenomenon. This systematic review and meta-analysis aimed to investigate the effect of sleep on novel word learning in adults, and explore whether these effects differed by retrieval domain (i.e., recall, recognition, and tests of lexical integration). Twenty-five unique studies met the inclusion criteria for the review, and 42 separate outcome measures were synthesized in the meta-analysis (k = 29 separate between-group comparisons, n = 1,396 participants). The results from the omnibus meta-analysis indicated that sleep was beneficial for novel word learning compared with wakefulness (g = 0.50). Effect sizes differed across the separate domain-specific meta-analyses, with moderate effects for recall (g = 0.57) and recognition memory (g = 0.52), and a small effect for tasks which measured lexical integration (g = 0.39). Overall, the results of this meta-analysis indicate that sleep generally benefits novel word acquisition and consolidation compared with wakefulness across differing retrieval domains. This systematic review highlights the potential for sleep to be used to improve second-language learning in healthy adults, and overall provides further insight into methods to facilitate language development.

Examining the effects of time of day and sleep on generalization

Extracting shared structure across our experiences allows us to generalize our knowledge to novel contexts. How do different brain states influence this ability to generalize? Using a novel category learning paradigm, we assess the effect of both sleep and time of day on generalization that depends on the flexible integration of recent information. Counter to our expectations, we found no evidence that this form of generalization is better after a night of sleep relative to a day awake. Instead, we observed an effect of time of day, with better generalization in the morning than the evening. This effect also manifested as increased false memory for generalized information. In a nap experiment, we found that generalization did not benefit from having slept recently, suggesting a role for time of day apart from sleep. In follow-up experiments, we were unable to replicate the time of day effect for reasons that may relate to changes in category structure and task engagement. Despite this lack of consistency, we found a morning benefit for generalization when analyzing all the data from experiments with matched protocols (n = 136). We suggest that a state of lowered inhibition in the morning may facilitate spreading activation between otherwise separate memories, promoting this form of generalization.

The contributions of the left fusiform subregions to successful encoding of novel words

The left fusiform cortex has been identified as a crucial structure in visual word learning and memory. Nevertheless, the specific roles of the fusiform subregions in word memory and their consistency across different writings have not been elaborated. To address these questions, the present study performed two experiments, in which study-test paradigm was used. Participants' brain activity was measured with fMRI while memorizing novel logographic words in Experiment 1 and novel alphabetic words in Experiment 2. A post-scan recognition memory test was then administered to acquire the memory performance. Results showed that, neural responses in the left anterior and middle fusiform subregions during encoding were positively correlated with recognition memory of novel words. Moreover, the positive brain-behavior correlations in the left anterior and middle fusiform cortex were evident for both logographic and alphabetic writings. The present findings clarify the relationship between the left fusiform subregions and novel word memory.

Order Matters! Influences of Linear Order on Linguistic Category Learning

Linguistic category learning has been shown to be highly sensitive to linear order, and depending on the task, differentially sensitive to the information provided by preceding category markers (premarkers, e.g., gendered articles) or succeeding category markers (postmarkers, e.g., gendered suffixes). Given that numerous systems for marking grammatical categories exist in natural languages, it follows that a better understanding of these findings can shed light on the factors underlying this diversity. In two discriminative learning simulations and an artificial language learning experiment, we identify two factors that modulate linear order effects in linguistic category learning: category structure and the level of abstraction in a category hierarchy. Regarding category structure, we find that postmarking brings an advantage for learning category diagnostic stimulus dimensions, an effect not present when categories are non-confusable. Regarding levels of abstraction, we find that premarking of super-ordinate categories (e.g., noun class) facilitates learning of subordinate categories (e.g., nouns). We present detailed simulations using a plausible candidate mechanism for the observed effects, along with a comprehensive analysis of linear order effects within an expectation-based account of learning. Our findings indicate that linguistic category learning is differentially guided by pre- and postmarking, and that the influence of each is modulated by the specific characteristics of a given category system.

Mini Pinyin: A modified miniature language for studying language learning and incremental sentence processing

Artificial grammar learning (AGL) paradigms are used extensively to characterise (neuro)cognitive bases of language learning. However, despite their effectiveness in characterising the capacity to learn complex structured sequences, AGL paradigms lack ecological validity and typically do not account for cross-linguistic differences in sentence comprehension. Here, we describe a new modified miniature language paradigm - Mini Pinyin - that mimics natural language as it is based on an existing language (Mandarin Chinese) and includes both structure and meaning. Mini Pinyin contains a number of cross-linguistic elements, including varying word orders and classifier-noun rules. To evaluate the effectiveness of Mini Pinyin, 76 (mean age = 24.9; 26 female) monolingual native English speakers completed a learning phase followed by a sentence acceptability judgement task. Generalised mixed effects modelling revealed that participants attained a moderate degree of accuracy on the judgement task, with performance scores ranging from 25% to 100% accuracy depending on the word order of the sentence. Further, sentences compatible with the canonical English word order were learned more efficiently than non-canonical word orders. We controlled for inter-individual differences in statistical learning ability, which accounted for ~20% of the variance in performance on the sentence judgement task. We provide stimuli and statistical analysis scripts as open-source resources and discuss how future research can utilise this paradigm to study the neurobiological basis of language learning. Mini Pinyin affords a convenient tool for improving the future of language learning research by building on the parameters of traditional AGL or existing miniature language paradigms.

Generalisation in language learning can withstand total sleep deprivation

Research suggests that sleep plays a vital role in memory. We tested the impact of total sleep deprivation on adults' memory for a newly learned writing system and on their ability to generalise this knowledge to read untrained novel words. We trained participants to read fictitious words printed in a novel artificial orthography, while depriving them of sleep the night after learning (Experiment 1) or the night before learning (Experiment 2). Following two nights of recovery sleep, and again 10 days later, participants were tested on trained words and untrained words, and performance was compared to control groups who had not undergone sleep deprivation. Participants showed a high degree of accuracy in learning the trained words and in generalising their knowledge to untrained words. There was little evidence of impact of sleep deprivation on memory or generalisation. These data support emerging theories which suggest sleep-associated memory consolidation can be accelerated or entirely bypassed under certain conditions, and that such conditions also facilitate generalisation.

Settling Into Semantic Space: An Ambiguity-Focused Account of Word-Meaning Access

Most words are ambiguous: Individual word forms (e.g., run) can map onto multiple different interpretations depending on their sentence context (e.g., the athlete/politician/river runs). Models of word-meaning access must therefore explain how listeners and readers can rapidly settle on a single, contextually appropriate meaning for each word that they encounter. I present a new account of word-meaning access that places semantic disambiguation at its core and integrates evidence from a wide variety of experimental approaches to explain this key aspect of language comprehension. The model has three key characteristics. (a) Lexical-semantic knowledge is viewed as a high-dimensional space; familiar word meanings correspond to stable states within this lexical-semantic space. (b) Multiple linguistic and paralinguistic cues can influence the settling process by which the system resolves on one of these familiar meanings. (c) Learning mechanisms play a vital role in facilitating rapid word-meaning access by shaping and maintaining high-quality lexical-semantic knowledge throughout the life span. In contrast to earlier models of word-meaning access, I highlight individual differences in lexical-semantic knowledge: Each person's lexicon is uniquely structured by specific, idiosyncratic linguistic experiences.

Early Language Experience in a Tseltal Mayan Village

Daylong at-home audio recordings from 10 Tseltal Mayan children (0;2-3;0; Southern Mexico) were analyzed for how often children engaged in verbal interaction with others and whether their speech environment changed with age, time of day, household size, and number of speakers present. Children were infrequently directly spoken to, with most directed speech coming from adults, and no increase with age. Most directed speech came in the mornings, and interactional peaks contained nearly four times the baseline rate of directed speech. Coarse indicators of children's language development (babbling, first words, first word combinations) suggest that Tseltal children manage to extract the linguistic information they need despite minimal directed speech. Multiple proposals for how they might do so are discussed.

Sleep and the extraction of hidden regularities: A systematic review and the importance of temporal rules

As part of its role in memory consolidation, sleep has been repeatedly identified as critical for the extraction of regularities from wake experiences. However, many null results have been published as well, with no clear consensus emerging regarding the conditions that yield this sleep effect. Here, we systematically review the role of sleep in the extraction of hidden regularities, specifically those involving associative relations embedded in newly learned information. We found that the specific behavioral task used in a study had far more impact on whether a sleep effect was discovered than either the category of the cognitive processes targeted, or the particular experimental design employed. One emerging pattern, however, was that the explicit detection of hidden rules is more likely to happen when the rules are of a temporal nature (i.e., event A at time t predicts a later event B) than when they are non-temporal. We discuss this temporal rule sensitivity in reference to the compressed memory replay occurring in the hippocampus during slow-wave-sleep, and compare this effect to what happens when the extraction of regularities depends on prior knowledge and relies on structures other than the hippocampus.

Contextual priming of word meanings is stabilized over sleep

Evidence is growing for the involvement of consolidation processes in the learning and retention of language, largely based on instances of new linguistic components (e.g., new words). Here, we assessed whether consolidation effects extend to the semantic processing of highly familiar words. The experiments were based on the word-meaning priming paradigm in which a homophone is encountered in a context that biases interpretation towards the subordinate meaning. The homophone is subsequently used in a word-association test to determine whether the priming encounter facilitates the retrieval of the primed meaning. In Experiment 1 (N = 74), we tested the resilience of priming over periods of 2 and 12 h that were spent awake or asleep, and found that sleep periods were associated with stronger subsequent priming effects. In Experiment 2 (N = 55) we tested whether the sleep benefit could be explained in terms of a lack of retroactive interference by testing participants 24 h after priming. Participants who had the priming encounter in the evening showed stronger priming effects after 24 h than participants primed in the morning, suggesting that sleep makes priming resistant to interference during the following day awake. The results suggest that consolidation effects can be found even for highly familiar linguistic materials. We interpret these findings in terms of a contextual binding account in which all language perception provides a learning opportunity, with sleep and consolidation contributing to the updating of our expectations, ready for the next day.

Skilled readers' sensitivity to meaningful regularities in English writing

Substantial research has been undertaken to understand the relationship between spelling and sound, but we know little about the relationship between spelling and meaning in alphabetic writing systems. We present a computational analysis of English writing in which we develop new constructs to describe this relationship. Diagnosticity captures the amount of meaningful information in a given spelling, whereas specificity estimates the degree of dispersion of this meaning across different spellings for a particular sound sequence. Using these two constructs, we demonstrate that particular suffix spellings tend to be reserved for particular meaningful functions. We then show across three paradigms (nonword classification, spelling, and eye tracking during sentence reading) that this form of regularity between spelling and meaning influences the behaviour of skilled readers, and that the degree of this behavioural sensitivity mirrors the strength of spelling-to-meaning regularities in the writing system. We close by arguing that English spelling may have become fractionated such that the high degree of spelling-sound inconsistency maximises the transmission of meaningful information.

The role of complementary learning systems in learning and consolidation in a quasi-regular domain

We examine the role of off-line memory consolidation processes in the learning and retention of a new quasi-regular linguistic system similar to the English past tense. Quasi-regular systems are characterized by a dominance of systematic, regular forms (e.g., walk-walked, jump-jumped) alongside a smaller number of high frequency irregulars (e.g., sit-sat, go-went), and are found across many cognitive domains, from spelling-sound mappings to inflectional morphology to semantic cognition. Participants were trained on the novel morphological system using an artificial language paradigm, and then tested after different delays. Based on a complementary systems account of memory, we predicted that irregular forms would show stronger off-line changes due to consolidation processes. Across two experiments, participants were tested either immediately after learning, 12 h later with or without sleep, or 24 h later. Testing involved generalization of the morphological patterns to previously unseen words (both experiments) as well as recall of the trained words (Experiment 2). In generalization, participants showed 'default' regularization across a range of novel forms, as well as irregularization for previously unseen items that were similar to unique high-frequency irregular trained forms. Both patterns of performance remained stable across the delays. Generalizations involving competing tendencies to regularize and irregularize were balanced between the two immediately after learning. Crucially, at both 12-h delays the tendency to irregularize in these cases was strengthened, with further strengthening after 24 h. Consolidated knowledge of both regular and irregular trained items contributed significantly to generalization performance, with evidence of strengthening of irregular forms and weakening of regular forms. We interpret these findings in the context of a complementary systems model, and discuss how maintenance, strengthening, and forgetting of the new memories across sleep and wake can play a role in acquiring quasi-regular systems.

Bedding down new words: Sleep promotes the emergence of lexical competition in visual word recognition

Lexical competition processes are widely viewed as the hallmark of visual word recognition, but little is known about the factors that promote their emergence. This study examined for the first time whether sleep may play a role in inducing these effects. A group of 27 participants learned novel written words, such as banara, at 8 am and were tested on their learning at 8 pm the same day (AM group), while 29 participants learned the words at 8 pm and were tested at 8 am the following day (PM group). Both groups were retested after 24 hours. Using a semantic categorization task, we showed that lexical competition effects, as indexed by slowed responses to existing neighbor words such as banana, emerged 12 h later in the PM group who had slept after learning but not in the AM group. After 24 h the competition effects were evident in both groups. These findings have important implications for theories of orthographic learning and broader neurobiological models of memory consolidation.

Oscillations, neural computations and learning during wake and sleep

Learning and memory theories consider sleep and the reactivation of waking hippocampal neural patterns to be crucial for the long-term consolidation of memories. Here we propose that precisely coordinated representations across brain regions allow the inference and evaluation of causal relationships to train an internal generative model of the world. This training starts during wakefulness and strongly benefits from sleep because its recurring nested oscillations may reflect compositional operations that facilitate a hierarchical processing of information, potentially including behavioral policy evaluations. This suggests that an important function of sleep activity is to provide conditions conducive to general inference, prediction and insight, which contribute to a more robust internal model that underlies generalization and adaptive behavior.

Sleep-Dependent Memory Consolidation and Incremental Sentence Comprehension: Computational Dependencies during Language Learning as Revealed by Neuronal Oscillations

We hypothesize a beneficial influence of sleep on the consolidation of the combinatorial mechanisms underlying incremental sentence comprehension. These predictions are grounded in recent work examining the effect of sleep on the consolidation of linguistic information, which demonstrate that sleep-dependent neurophysiological activity consolidates the meaning of novel words and simple grammatical rules. However, the sleep-dependent consolidation of sentence-level combinatorics has not been studied to date. Here, we propose that dissociable aspects of sleep neurophysiology consolidate two different types of combinatory mechanisms in human language: sequence-based (order-sensitive) and dependency-based (order-insensitive) combinatorics. The distinction between the two types of combinatorics is motivated both by cross-linguistic considerations and the neurobiological underpinnings of human language. Unifying this perspective with principles of sleep-dependent memory consolidation, we posit that a function of sleep is to optimize the consolidation of sequence-based knowledge (the when) and the establishment of semantic schemas of unordered items (the what) that underpin cross-linguistic variations in sentence comprehension. This hypothesis builds on the proposal that sleep is involved in the construction of predictive codes, a unified principle of brain function that supports incremental sentence comprehension. Finally, we discuss neurophysiological measures (EEG/MEG) that could be used to test these claims, such as the quantification of neuronal oscillations, which reflect basic mechanisms of information processing in the brain.

A role for consolidation in cross-modal category learning

The ability to categorize objects and events is a fundamental human skill that depends upon the representation of multimodal conceptual knowledge. This study investigated the acquisition and consolidation of categorical information that required participants to integrate information across visual and auditory dimensions. The impact of wake- and sleep-dependent consolidation was investigated using a paradigm in which training and testing were separated by a delay spanning either an evening of sleep or daytime wakefulness, with a paired-associate episodic memory task used as a measure of classic sleep-dependent consolidation. Participants displayed good evidence of category learning, but did not show any wake- or sleep-dependent changes in memory for category information immediately following the delay. This is in contrast to paired-associate learning, where a sleep-dependent benefit was observed in memory recall. To replicate real-world concept learning, in which knowledge is acquired across multiple distinct episodes, participants were given a second opportunity for category learning following the consolidation delay. Here we found an interaction between consolidation and learning; with greater improvements in category knowledge as a result of the second learning session for those participants who had a sleep-filled delay. These results suggest a role for sleep in the consolidation of recently acquired categorical knowledge; however this benefit does not emerge as an immediate benefit in memory recall, but by enhancing the effectiveness of future learning. This study therefore provides insights into the processes responsible for the formation and development of conceptual representations.

Sleep Benefits Memory for Semantic Category Structure While Preserving Exemplar-Specific Information

Semantic memory encompasses knowledge about both the properties that typify concepts (e.g. robins, like all birds, have wings) as well as the properties that individuate conceptually related items (e.g. robins, in particular, have red breasts). We investigate the impact of sleep on new semantic learning using a property inference task in which both kinds of information are initially acquired equally well. Participants learned about three categories of novel objects possessing some properties that were shared among category exemplars and others that were unique to an exemplar, with exposure frequency varying across categories. In Experiment 1, memory for shared properties improved and memory for unique properties was preserved across a night of sleep, while memory for both feature types declined over a day awake. In Experiment 2, memory for shared properties improved across a nap, but only for the lower-frequency category, suggesting a prioritization of weakly learned information early in a sleep period. The increase was significantly correlated with amount of REM, but was also observed in participants who did not enter REM, suggesting involvement of both REM and NREM sleep. The results provide the first evidence that sleep improves memory for the shared structure of object categories, while simultaneously preserving object-unique information.

The Role of Frequency in Learning Morphophonological Alternations: Implications for Children With Specific Language Impairment

PURPOSE

The aim of this article was to explore how the type of allomorph (e.g., past tense buzz[d] vs. nod[əd]) influences the ability to perceive and produce grammatical morphemes in children with typical development and with specific language impairment (SLI).

METHOD

The participants were monolingual Australian English-speaking children. The SLI group included 13 participants (mean age = 5;7 [years;months]); the control group included 19 children with typical development (mean age = 5;4). Both groups performed a grammaticality judgment and elicited production task with the same set of nonce verbs in third-person singular and past tense forms.

RESULTS

Five-year-old children are still learning to generalize morphophonological patterns to novel verbs, and syllabic /əz/ and /əd/ allomorphs are significantly more challenging to produce, particularly for the SLI group. The greater phonetic content of these syllabic forms did not enhance perception.

CONCLUSIONS

Acquisition of morphophonological patterns involving low-frequency allomorphs is still underway in 5-year-old children with typical development, and it is even more protracted in SLI populations, despite these patterns being highly predictable. Children with SLI will therefore benefit from targeted intervention with low-frequency allomorphs.

Consolidation of vocabulary during sleep: The rich get richer?

Sleep plays a role in strengthening new words and integrating them with existing vocabulary knowledge, consistent with neural models of learning in which sleep supports hippocampal transfer to neocortical memory. Such models are based on adult research, yet neural maturation may mean that the mechanisms supporting word learning vary across development. Here, we propose a model in which children may capitalise on larger amounts of slow-wave sleep to support a greater demand on learning and neural reorganisation, whereas adults may benefit from a richer knowledge base to support consolidation. Such an argument is reinforced by the well-reported "Matthew effect", whereby rich vocabulary knowledge is associated with better acquisition of new vocabulary. We present a meta-analysis that supports this association between children's existing vocabulary knowledge and their integration of new words overnight. Whilst multiple mechanisms likely contribute to vocabulary consolidation and neural reorganisation across the lifespan, we propose that contributions of existing knowledge should be rigorously examined in developmental studies. Such research has potential to greatly enhance neural models of learning.

Sleep-Driven Computations in Speech Processing

Acquiring language requires segmenting speech into individual words, and abstracting over those words to discover grammatical structure. However, these tasks can be conflicting-on the one hand requiring memorisation of precise sequences that occur in speech, and on the other requiring a flexible reconstruction of these sequences to determine the grammar. Here, we examine whether speech segmentation and generalisation of grammar can occur simultaneously-with the conflicting requirements for these tasks being over-come by sleep-related consolidation. After exposure to an artificial language comprising words containing non-adjacent dependencies, participants underwent periods of consolidation involving either sleep or wake. Participants who slept before testing demonstrated a sustained boost to word learning and a short-term improvement to grammatical generalisation of the non-adjacencies, with improvements after sleep outweighing gains seen after an equal period of wake. Thus, we propose that sleep may facilitate processing for these conflicting tasks in language acquisition, but with enhanced benefits for speech segmentation.