Linking working memory and long-term memory: A computational model of the learning of new words

The nonword repetition (NWR) test has been shown to be a good predictor of children’s vocabulary size. NWR performance has been explained using phonological working memory, which is seen as a critical component in the learning of new words. However, no detailed specification of the link between phonological working memory and long-term memory (LTM) has been proposed. In this paper, we present a computational model of children’s vocabulary acquisition (EPAM-VOC) that specifies how phonological working memory and LTM interact. The model learns phoneme sequences, which are stored in LTM and mediate how much information can be held in working memory. The model’s behaviour is compared with that of children in a new study of NWR, conducted in order to ensure the same nonword stimuli and methodology across ages. EPAM-VOC shows a pattern of results similar to that of children: performance is better for shorter nonwords and for wordlike nonwords, and performance improves with age. EPAM-VOC also simulates the superior performance for single consonant nonwords over clustered consonant nonwords found in previous NWR studies. EPAM-VOC provides a simple and elegant computational account of some of the key processes involved in the learning of new words: it specifies how phonological working memory and LTM interact; makes testable predictions; and suggests that developmental changes in NWR performance may reflect differences in the amount of information that has been encoded in LTM rather than developmental changes in working memory capacity. Keywords: EPAM, working memory, long-term memory, nonword repetition, vocabulary acquisition, developmental change

Authors' response [The ubiquity of frequency effects in first language acquisition]

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Determinants of acquisition order in wh-questions: Re-evaluating the role of caregiver speech

Item does not contain fulltextAccounts that specify semantic and/or syntactic complexity as the primary determinant of the order in which children acquire particular words or grammatical constructions have been highly influential in the literature on question acquisition. One explanation of wh-question acquisition in particular suggests that the order in which English speaking children acquire wh-questions is determined by two interlocking linguistic factors; the syntactic function of the wh-word that heads the question and the semantic generality (or 'lightness') of the main verb (Bloom, Merkin Wootten, 1982; Bloom, 1991). Another more recent view, however, is that acquisition is influenced by the relative frequency with which children hear particular wh-words and verbs in their input (e.g. Rowland & Pine, 2000). In the present study over 300 hours of naturalistic data from twelve two- to three-year-old children and their mothers were analysed in order to assess the relative contribution of complexity and input frequency to wh-question. acquisition. The analyses revealed, first, that the acquisition order of wh-questions could be predicted successfully from the frequency with which particular wh-words and verbs occurred in the children's input and, second, that syntactic and semantic complexity did not reliably predict acquisition once input frequency was taken into account. These results suggest that the relationship between acquisition and complexity may be a by-product of the high correlation between complexity and the frequency with which mothers use particular wh-words and verbs. We interpret the results in terms of a constructivist view of language acquisition.27 p

Interactions between givenness and clause order in children's processing of complex sentences

Understanding complex sentences that contain multiple clauses referring to events in the world and the relations between them is an important development in children's language learning. A number of theoretical positions have suggested that factors like syntactic structure (clause order), iconicity (whether the order of clauses reflects the order of events), and givenness (whether information is shared between speakers) affect ease of comprehension. We tested these accounts by investigating how these factors interact in British English-speaking children's comprehension of complex sentences with adverbial clauses (after, before, because, if), while controlling for language level, working memory and inhibitory control. 92 children in three age groups (4, 5 and 8 years) and 17 adults completed a picture selection task. Participants heard an initial context sentence, followed by a two-clause sentence which varied in: (1) the order of the main and subordinate clause; (2) the order of given and new information; and (3) whether the given information occurred in the main or subordinate clause. Accuracy and response times were measured. Our results showed that given-before-new improves comprehension for four- and five-year-olds, but only when the given information is in the initial subordinate clause (e.g., “Sue crawls on the floor. Before she crawls on the floor, she hops up and down”). Temporal adverbials (after, before) were processed faster than causal adverbials (because, if). These effects were not found for the eight-year-olds, whose performance was more similar to that of the adults. Providing a context sentence also improved performance compared to presenting the test sentences in isolation. We conclude that existing accounts based on either ease of processing or information structure cannot fully account for these findings, and suggest a more integrated explanation which reflects children's developing language and literacy skills