Contrasting dynamics of memory consolidation for novel word forms and meanings revealed by behavioral and neurophysiological markers

Are brain activity changes underlying rare word production after learning specific or do they extend to semantically related rare words?

Learning words in the mother tongue is a fundamental lifelong skill that involves complex cognitive and neural changes. In adults, newly learned words affect the organization of the lexical-semantic network and, compared to words that have been in the lexicon for longer, they activate the same cortical areas, but more extensively and/or intensively. It is however still unclear (1) which brain and cognitive processes underlying word production change when infrequent/unknown words are compared before and after learning and (2) whether integrating newly learned words impacts word specific processes or has a broader impact on unlearned words. The present study aims to investigate the electrophysiological changes underlying the production of rare words induced by learning and the effect of learning on an unlearned list of rare words belonging to the same semantic categories. To this end, 24 neurotypical adults learned one of two matched lists of 40 concrete rare words from 4 semantic categories. EEG (electroencephalographic) recordings were acquired during a referential word production task (picture naming) of the learned and unlearned words before and after the learning phase. The results show that the production of rare word is associated with event-related (ERP) differences between before and after learning in the period from 300 to 800 msec following the presentation of the imaged concept (picture). These differences consisted in a larger involvement of left temporal and parietal regions after learning between 300 and 400 msec i.e., the time window likely corresponding to lexical and phonological encoding processes. Crucially, the ERP changes are not restricted to the production of the learned rare words, but are also observed when participants try to retrieve words of a list of semantically and lexically matched rare words that they have not learned. The ERP changes on unlearned rare words are weaker and suggest that learning new words induces boarder effects also on unlearned words.

Sleep-dependent consolidation effects on foreign language word acquisition in a virtual reality environment

Sleep-dependent consolidation is important for novel word learning, but previous studies have neglected the potential modulating role of learning environments. The present study examines sleep-dependent consolidation effects by comparing learning in a virtual reality (VR) environment and in a traditional picture-word (PW) environment. Two groups of Chinese-English bilinguals were randomly assigned to a VR or PW environment. In both learning environments, they learned novel words in Korean, a language with which they had no prior experience. All participants learned one set of novel words on Day 1 and another set on Day 2. An explicit recognition task and an implicit primed lexical-decision task were employed to measure sleep-dependent consolidation effects from the two environments. Results revealed sleep-dependent consolidation effects in both explicit and implicit measures, but only the primed lexical-decision task showed an influence of learning environment, suggesting that novel words learned via VR had better consolidation. Taken together, our findings suggest that a VR environment that fosters a rich sensory experience facilitates sleep-dependent consolidation effects. We argue that these results provide new evidence and implications for the complementary learning system (CLS) model.

Learning new meanings for known L2 words: Long‐term semantic representation is updated to integrate new information after consolidation

Previous research about learning new meanings for known words in second language (L2) has found that semantic relatedness, i.e., congruency, between new and existing meanings benefits encoding and explicit memory of new meanings, and reduces instant interference on accessing existing meanings. However, they did not take the memory consolidation process into account. Thus, integration of new meaning into long-term semantic memory, update of existing meaning representation, and the impact of semantic relatedness between new and existing meanings in this process remain unclear. The present study used the event-related potential (ERP) technique to explore these questions. We asked Chinese students to learn English known words' subdominant meanings variedly related to existing meanings and probed semantic representations with EEG recorded in primed lexical decision tasks four times before and after consolidation. We found that new meaning needs to go through offline consolidation to get integrated. Semantic relatedness/congruency boosted new meaning integration, not by directly expediting it during encoding or preliminary offline consolidation, but by promoting the update of existing meaning representation first, which presumably paved the way for better incorporation of new meaning in the long run. The whole pattern of results implies that long-term semantic representation of existing meaning is updated to integrate related new meaning after consolidation, which not only draws a clearer picture of L2 ambiguous word acquisition but also bears broader implications for research on memory updating.

Acquisition of novel word meaning via cross situational word learning: An event-related potential study

Cross-situational statistical word learning (CSWL) refers to the process whereby participants learn new words by tracking ambiguous word-object co-occurrences across time. This study used event-related potentials to explore the acquisition of novel word meanings via CSWL in healthy adults. After learning to associate novel auditory words (e.g., 'ket') with familiar objects (e.g., sword), participants performed a semantic judgement task where the learned novel words were paired with a familiar word belonging to either the same (e.g., dagger) or a different (e.g., harp) semantic category. As a comparison, the task also included word pairs comprising two familiar words. The analyses revealed that the unrelated novel word pairs elicited a similar N400 to that of the unrelated familiar word pairs, but with a different hemispheric distribution (left hemisphere for novel words, right hemisphere for familiar words). These findings demonstrate rapid meaning acquisition via CSWL, which is reflected at a neurophysiological level.

Learning new words: Memory reactivation as a mechanism for strengthening and updating a novel word's meaning

In the present study we explored the postlearning changes in a novel word's definition using a cue-induced memory reactivation. Native speakers of Spanish (N = 373) learned low-frequency words with their corresponding definitions. The following day, reactivated groups were exposed to a reminder and provided a subjective assessment of reactivation for each word, while control groups did not receive a reactivation. Study A demonstrated that memory reactivation enhances both explicit recall and semantic integration of new meanings. Study B investigated the effect of memory reactivation in the modification of the new meanings, through three different experiments. Results show an improvement of the updated definitions according to each word's reactivation strength. In addition, congruence with previous knowledge was suggested to be a boundary condition, while consolidation time had a positive modulatory effect. Our findings call attention to reactivation as a factor allowing for malleability as well as persistence of long-term memories for words.

Cross-Dialectal Novel Word Learning and Borrowing

The objective of this paper was to study the cognitive processes underlying cross-dialectal novel word borrowing and loanword establishment in a Standard-Chinese-to-Shanghainese (SC-SH) auditory lexical learning and borrowing experiment. To investigate these underlying cognitive processes, SC-SH bi-dialectals were compared with SC monolectals as well as bi-dialectals of SC and other Chinese dialects (OD) to investigate the influence of short-term and long-term linguistic experience. Both comprehension and production borrowings were tested. This study found that early and proficient bi-dialectism, even if it is not directly related to the recipient dialect of lexical borrowing, has a protective effect on the ability of cross-dialectal lexical borrowing in early adulthood. Bi-dialectals tend to add separate lexical representations for incidentally encountered dialectal variants, while monolectals tend to assimilate dialectal variants to standard forms. Bi-dialectals, but not monolectals, use etymologically related morphemes between the source and recipient dialects to create nonce-borrowing compounds. Dialectal variability facilitates lexical borrowing via enriching instead of increasing the short-term lexical experience of learners. The long-term bi-dialectal experience of individuals, as well as their short-term exposure to each specific loanword, may collectively shape the route of lexical evolution of co-evolving linguistic varieties.

The interplay between domain-general and domain-specific mechanisms during the time-course of verbal associative learning: An event-related potential study

Humans continuously learn new information. Here, we examined the temporal brain dynamics of explicit verbal associative learning between unfamiliar items. In the first experiment, 25 adults learned object-pseudoword associations during a 5-day training program allowing us to track the N400 dynamics across learning blocks within and across days. Successful learning was accompanied by an initial frontal N400 that decreased in amplitude across blocks during the first day and shifted to parietal sites during the last training day. In Experiment 2, we replicated our findings with 38 new participants randomly assigned to a consistent learning or an inconsistent learning group. The N400 amplitude modulations that we found, both within and between learning sessions, are taken to reflect the emergence of novel lexical traces even when learning concerns items for which no semantic information is provided. The shift in N400 topography suggests that different N400 neural generators may contribute to specific word learning steps through a balance between domain-general and language-specific mechanisms.

Animacy as a memory enhancer during novel word learning: evidence from orthographic and semantic memory tasks

It was previously shown that words representing living things are better remembered than those representing nonliving things. Here we address the influence of animacy on novel word memory formation in adults, dissecting its effect on semantic and orthographic learning. Participants received training on a set of new picture-name-description mappings corresponding to animate or inanimate items, simulating word learning in the first language. The integration of novel words was indexed in a semantic judgment task, performed at 30 min or 48 h after learning. Results show that novel word forms and meanings corresponding to animate items are better recalled than inanimate ones. In addition, animate items are processed faster than inanimate items in a semantic judgment task 30 min after learning, while the speed advantage is not evident in the long-term. Thus, animacy is a pervasive memory enhancer during novel word acquisition but its effects on lexical processing are short-lived.