Publications

Abstract

Memory representations of words are thought to undergo changes with consolidation: Episodic memories of novel words are transformed into lexical representations that interact with other words in the mental dictionary. Behavioral studies have shown that this lexical integration process is enhanced when there is more time for consolidation. Neuroimaging studies have further revealed that novel word representations are initially represented in a hippocampally-centered system, whereas left posterior middle temporal cortex activation increases with lexicalization. In this study, we measured behavioral and brain responses to newly-learned words in children. Two groups of Dutch children, aged between 8-10 and 14-16 years, were trained on 30 novel Japanese words depicting novel concepts. Children were tested on word-forms, word-meanings, and the novel words’ influence on existing word processing immediately after training, and again after a week. In line with the adult findings, hippocampal involvement decreased with time. Lexical integration, however, was not observed immediately or after a week, neither behaviorally nor neurally. It appears that time alone is not always sufficient for lexical integration to occur. We suggest that other factors (e.g., the novelty of the concepts and familiarity with the language the words are derived from) might also influence the integration process.

Abstract

The aim of the present study was to examine whether repetition of radicals during training of Chinese characters leads to better word acquisition performance in beginning learners of Chinese as a foreign language. Thirty Dutch university students were trained on 36 Chinese one-character words for their pronunciations and meanings. They were also exposed to the specifics of the radicals, that is, for phonetic radicals, the associated pronunciation was explained, and for semantic radicals the associated categorical meanings were explained. Results showed that repeated exposure to phonetic and semantic radicals through character pronunciation and meaning trainings indeed induced better understanding of those radicals that were shared among different characters. Furthermore, characters in the training set that shared phonetic radicals were pronounced better than those that did not. Repetition of semantic radicals across different characters, however, hindered the learning of exact meanings. Students generally confused the meanings of other characters that shared the semantic radical. The study shows that in the initial stage of learning, overlapping information of the shared radicals are effectively learned. Acquisition of the specifics of individual characters, however, requires more training.

Abstract

This study explores the effect of feedback with hints on students’ recall of words. In three classroom experiments, high school students individually practiced vocabulary words through computerized retrieval practice with either standard show-answer feedback (display of answer) or hints feedback after incorrect responses. Hints feedback gave students a second chance to find the correct response using orthographic (Experiment 1), mnemonic (Experiment 2), or cross-language hints (Experiment 3). During practice, hints led to a shift of practice time from further repetitions to longer feedback processing but did not reduce (repeated) errors. There was no effect of feedback on later recall except when the hints from practice were also available on the test, indicating limited transfer of practice with hints to later recall without hints (in Experiments 1 and 2). Overall, hints feedback was not preferable over show-answer feedback. The common notion that hints are beneficial may not hold when the total practice time is limited.

Abstract

Research into strategies that can combat episodic memory decline in healthy older adults has gained widespread attention over the years. Evidence suggests that a short period of rest immediately after learning can enhance memory consolidation, as compared to engaging in cognitive tasks. However, a recent study in younger adults has shown that post-encoding engagement in a working memory task leads to the same degree of memory consolidation as from post-encoding rest. Here, we tested whether this finding can be extended to older adults. Using a delayed recognition test, we compared the memory consolidation of word–picture pairs learned prior to 9 min of rest or a 2-Back working memory task, and examined its relationship with executive functioning and mindwandering propensity. Our results show that (1) similar to younger adults, memory for the word–picture associations did not differ when encoding was followed by post-encoding rest or 2-Back task and (2) older adults with higher mindwandering propensity retained more word–picture associations encoded prior to rest relative to those encoded prior to the 2-Back task, whereas participants with lower mindwandering propensity had better memory performance for the pairs encoded prior to the 2-Back task. Overall, our results indicate that the degree of episodic memory consolidation during both active and passive post-encoding periods depends on individual mindwandering tendency.

Abstract

In four experiments we investigated the formation of novel word memories across modalities, using competition between novel words and their existing phonological/orthographic neighbours as a test of lexical integration. Auditorily acquired novel words entered into competition both in the spoken modality (Experiment 1) and in the written modality (Experiment 4) after a consolidation period of 24 h. Words acquired from print, on the other hand, showed competition effects after 24 h in a visual word recognition task (Experiment 3) but required additional training and a consolidation period of a week before entering into spoken-word competition (Experiment 2). These cross-modal effects support the hypothesis that lexicalised rather than episodic representations underlie post-consolidation competition effects. We suggest that sublexical phoneme–grapheme conversion during novel word encoding and/or offline consolidation enables the formation of modality-specific lexemes in the untrained modality, which subsequently undergo the same cortical integration process as explicitly perceived word forms in the trained modality. Although conversion takes place in both directions, speech input showed an advantage over print both in terms of lexicalisation and explicit memory performance. In conclusion, the brain is able to integrate and consolidate internally generated lexical information as well as external perceptual input.

Abstract

To investigate the neural underpinnings of word decoding, and how it changes as a function of repeated exposure, we trained Dutch participants repeatedly over the course of a month of training to articulate a set of novel disyllabic input strings written in Greek script to avoid the use of familiar orthographic representations. The syllables in the input were phonotactically legal combinations but non-existent in the Dutch language, allowing us to assess their role in novel word decoding. Not only trained disyllabic pseudowords were tested but also pseudowords with recombined patterns of syllables to uncover the emergence of syllabic representations. We showed that with extensive training, articulation became faster and more accurate for the trained pseudowords. On the neural level, the initial stage of decoding was reflected by increased activity in visual attention areas of occipito-temporal and occipito-parietal cortices, and in motor coordination areas of the precentral gyrus and the inferior frontal gyrus. After one month of training, memory representations for holistic information (whole word unit) were established in areas encompassing the angular gyrus, the precuneus and the middle temporal gyrus. Syllabic representations also emerged through repeated training of disyllabic pseudowords, such that reading recombined syllables of the trained pseudowords showed similar brain activation to trained pseudowords and were articulated faster than novel combinations of letter strings used in the trained pseudowords.

Abstract

The complementary learning systems account of declarative memory suggests two distinct memory networks, a fast-mapping, episodic system involving the hippocampus, and a slower semantic memory system distributed across the neocortex in which new information is gradually integrated with existing representations. In this study, we investigated the extent to which these two networks are involved in the integration of novel words into the lexicon after extensive learning, and how the involvement of these networks changes after 24 hours. In particular, we explored whether having richer information at encoding influences the lexicalization trajectory. We trained participants with two sets of novel words, one where exposure was only to the words’ phonological forms (the form-only condition), and one where pictures of unfamiliar objects were associated with the words’ phonological forms (the picture-associated condition). A behavioral measure of lexical competition (indexing lexicalization) indicated stronger competition effects for the form-only words. Imaging (fMRI) results revealed greater involvement of phonological lexical processing areas immediately after training in the form-only condition, suggesting tight connections were formed between novel words and existing lexical entries already at encoding. Retrieval of picture-associated novel words involved the episodic/hippocampal memory system more extensively. Although lexicalization was weaker in the picture-associated condition, overall memory strength was greater when tested after a 24 hours’ delay, probably due to the availability of both episodic and lexical memory networks to aid retrieval. It appears that, during lexicalization of a novel word, the relative involvement of different memory networks differs according to the richness of the information about that word available at encoding.