Neural correlates of word learning in children

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. Keywords: Novel word memory, Brain development, Hippocampus, Lexicalization, Consolidation, fMR

Competition from unseen or unheard novel words: Lexical consolidation across modalities

Item does not contain fulltextIn 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.15 p