| Using an instance-based approach to word learning (Reichle & Perfetti, 2003), two experiments tested the general hypothesis that differences in word experience give rise to encoded memories of words that differ in strength and quality, and that these differences affect meaning acquisition and subsequent word processing. Adult learners were exposed to rare unknown words in contexts that differed by type (definition or sentence context), variability (varied or repeated content), and semantic constraint (high or low) in an incidental word learning paradigm. Words were learned over the exposure of four learning trials that was followed by a testing phase during which ERPs were recorded. Of interest were the FN400, P600, and N400 components, which are neural signatures of familiarity, recollection, and meaning acquisition, respectively. Learners completed three tasks (semantic judgment, sentence judgment, and definition generation) that measured their acquisition of definitional and contextual meaning knowledge. For Experiment 1, the type of context and variability of content were manipulated. Our results showed FN400 effects for definition conditions, and N400 effects for varied context conditions, indicating differential effects of word experience for familiarity and meaning acquisition. For Experiment 2, the semantic constraint and the variability of single-sentence contexts were manipulated. Familiarity effects as indexed by the FN400 indicated an effect for repetition; words learned in repeated contexts of high or low semantic constraint showed increased familiarity, whereas no familiarity effects were found for varied content conditions. Differences in N400 effects were found for contextual-related decisions; larger N400 effects were found for varied content conditions that facilitated the acquisition of the contextual knowledge of the word. Correlations with ERP effects, behavioral measures, and individual difference measures showed that the acquisition of meaning knowledge is related to vocabulary, comprehension, and lexical skill. These results suggest that different word experiences have differential effects on word familiarity and meaning acquisition, and that these differences can be interpreted in terms of the strength, quantity, and availability of the encoded memory traces for those word experiences. |
