Learning new meanings for known words: Biphasic effects of prior knowledge.

In acquiring word meanings, learners are often confronted by a single word form that is mapped to two or more meanings. For example, long after how to roller-"skate", one may learn that "skate" is also a kind of fish. Such learning of new meanings for familiar words involves two potentially contrasting processes, relative to new form-new meaning learning: 1) Form-based familiarity may facilitate learning a new meaning, and 2) meaning-based interference may inhibit learning a new meaning. We examined these two processes by having native English speakers learn new, unrelated meanings for familiar (high frequency) and less familiar (low frequency) English words, as well as for unfamiliar (novel or pseudo-) words. Tracking learning with cued-recall tasks at several points during learning revealed a biphasic pattern: higher learning rates and greater learning efficiency for familiar words relative to novel words early in learning and a reversal of this pattern later in learning. Following learning, interference from original meanings for familiar words was detected in a semantic relatedness judgment task. Additionally, lexical access to familiar words with new meanings became faster compared to their exposure controls, but no such effect occurred for less familiar words. Overall, the results suggest a biphasic pattern of facilitating and interfering processes: Familiar word forms facilitate learning earlier, while interference from original meanings becomes more influential later. This biphasic pattern reflects the co-activation of new and old meanings during learning, a process that may play a role in lexicalization of new meanings.

Contextual learning of L2 word meanings: Second language proficiency modulates behavioural and ERP indicators of learning.

New word learning occurs incidentally through exposure to language. Hypothesizing that effectiveness of contextual word learning in a second language (L2) depends on the quality of existing lexical semantic knowledge, we tested more and less proficient adult bilinguals in an incidental word learning task. One day after being exposed to rare words in an L2 (English) reading task, the bilinguals read sentences with the newly-learned words in the sentence-final position, followed by related or unrelated meaning probes. Both proficiency groups showed some learning through faster responses on related trials and a frontal N400 effect observed during probe word reading. However, word learning was more robust for the higher-proficiency group, who showed a larger semantic relatedness effect in unfamiliar contexts and a canonical N400 (central-parietal). The results suggest that the ability to learn the meanings of new words from context depends on the L2 lexical semantic knowledge of the reader.

ERP evidence for memory and predictive mechanisms in word-to-text integration.

During reading, word-to-text integration processes proceed quickly and incrementally through both prospective (predictive) and retrospective (memory) processes. Across a sentence boundary, where prediction may be less functional, memorial processes may be especially important. We tested predictive and memory mechanisms with event-related potentials (ERPs) recorded on the first content word across a sentence boundary by manipulating the direction of association between this word and one from the preceding sentence. For comparison with this text comprehension (TC) task, we tested these same word pairs in a word meaning judgment (MJ) task. In both tasks we found reduced N400 amplitudes over central scalp electrodes when the two words were either forward-associated (FA) or backward-associated (BA), relative to task-specific baseline conditions. In the MJ task, FA pairs produced a greater reduction in the N400 reduction than BA pairs over right parietal areas. However, in the TC task, BA pairs produced a greater N400 reduction than FA pairs over left parietal electrodes. A temporal principal component analysis of TC and MJ data showed a component reflecting the central N400. Additional components from TC data reflected FA-BA differences during early (N200) and late (parietal N400 and LPC) phases of processing. Comprehension skill predicted association effects in the MJ task, especially FA, and the BA central N400 effects in the TC task. The results demonstrate that, beyond N400 indicators of prediction effects, ERPs reflect the role of memory processes in word-to-text integration across sentences, part of a dynamic interplay between anticipatory and memorial processes that support comprehension.

Word-to-text integration: Message level and lexical level influences in ERPs.

Although the reading of connected text proceeds in a largely incremental fashion, the relative degree to which message level and lexical level factors contribute to integration processes across sentences remains an open question. We examined the influence of both factors on single words using event-related potentials (ERPs). Word pairs with either strong or weak forward association strength were critical items: embedded as coreferential words within two-sentence passages in a text comprehension task, and as isolated word pairs in a word meaning judgment task. While the N400 ERP component reflected an effect of forward association strength on lexico-semantic processing in the word task (i.e., reduced N400 amplitudes were seen for strongly associated pairs relative to weakly associated pairs), in the comprehension task, passages embedded with any associated word pairs elicited reduced N400 amplitudes relative to coherent baseline passages lacking one of the critical words. These comprehension effects reflect responses from the highest skilled comprehenders. The results demonstrate the effects of message level factors, and reading abilities, on the processing of single words.

Early stage visual-orthographic processes predict long-term retention of word form and meaning: a visual encoding training study.

Adult learners of Chinese learned new characters through writing, visual chunking or reading-only. Following training, ERPs were recorded during character recognition tasks, first shortly after the training and then three months later. We hypothesized that the character training effects would be seen in ERP components associated with word recognition and episodic memory. Results confirmed a larger N170 for visual chunking training than other training and a larger P600 for learned characters than novel characters. Another result was a training effect on the amplitude of the P100, which was greater following writing training than other training, suggesting that writing training temporarily lead to increased visual attention to the orthographic forms. Furthermore, P100 amplitude at the first post-test was positively correlated with character recall 3 months later. Thus the marker of early visual attention (P100) was predictive of retention of orthographic knowledge acquired in training.