Virginia A. Marchman

From rote learning to system building: acquiring verb morphology in children and connectionist nets

The traditional account of the acquisition of English verb morphology supposes that a dual architecture underlies the transition from early rote-learning processes (in which past tense forms of verbs are correctly produced) to the systematic treatment of verbs (in which irregular verbs are prone to error). A connectionist account supposes that this transition can occur in a single mechanism (in the form of a neural network) driven by gradual quantitative changes in the size of the training set to which the network is exposed. In this paper, a series of simulations is reported in which a multi-layered perceptron learns to map verb stems to past tense forms analogous to the mappings found in the English past tense system. By expanding the training set in a gradual, incremental fashion and evaluating network performance on both trained and novel verbs at successive points in learning, it is demonstrated that the network undergoes reorganizations that result in a shift from a mode of rote learning to a systematic treatment of verbs. Furthermore, we show that this reorganizational transition is dependent upon the number of regular and irregular verbs in the training set and is sensitive to the phonological sub-regularities characterizing the irregular verbs. The pattern of errors observed is compared to that of children acquiring the English past tense, as well as childrens performance on experimental studies with nonsense verbs. It is concluded that a connectionist approach offers a viable alternative account of the acquisition of English verb morphology, given the current state of empirical evidence relating to processes of acquisition in young children.

SES differences in language processing skill and vocabulary are evident at 18 months.

This research revealed both similarities and striking differences in early language proficiency among infants from a broad range of advantaged and disadvantaged families. English-learning infants (n = 48) were followed longitudinally from 18 to 24 months, using real-time measures of spoken language processing. The first goal was to track developmental changes in processing efficiency in relation to vocabulary learning in this diverse sample. The second goal was to examine differences in these crucial aspects of early language development in relation to family socioeconomic status (SES). The most important findings were that significant disparities in vocabulary and language processing efficiency were already evident at 18 months between infants from higher- and lower-SES families, and by 24 months there was a 6-month gap between SES groups in processing skills critical to language development.

Picking up speed in understanding : Speech processing efficiency and vocabulary growth across the 2nd year

To explore how online speech processing efficiency relates to vocabulary growth in the 2nd year, the authors longitudinally observed 59 English-learning children at 15, 18, 21, and 25 months as they looked at pictures while listening to speech naming one of the pictures. The time course of eye movements in response to speech revealed significant increases in the efficiency of comprehension over this period. Further, speed and accuracy in spoken word recognition at 25 months were correlated with measures of lexical and grammatical development from 12 to 25 months. Analyses of growth curves showed that children who were faster and more accurate in online comprehension at 25 months were those who showed faster and more accelerated growth in expressive vocabulary across the 2nd year.

Speed of word recognition and vocabulary knowledge in infancy predict cognitive and language outcomes in later childhood.

The nature of predictive relations between early language and later cognitive function is a fundamental question in research on human cognition. In a longitudinal study assessing speed of language processing in infancy, Fernald, Perfors and Marchman (2006) found that reaction time at 25 months was strongly related to lexical and grammatical development over the second year. In this follow-up study, children originally tested as infants were assessed at 8 years on standardized tests of language, cognition, and working memory. Speed of spoken word recognition and vocabulary size at 25 months each accounted for unique variance in linguistic and cognitive skills at 8 years, effects that were attributable to strong relations between both infancy measures and working memory. These findings suggest that processing speed and early language skills are fundamental to intellectual functioning, and that language development is guided by learning and representational principles shared across cognitive and linguistic domains.

Early Lexical Development in Spanish-Speaking Infants and Toddlers.

This paper describes the early lexical development of a group of 328 normal Spanish-speaking children aged 0;8 to 2;7. First the development and structure of a new parent report instrument, Inventario del Desarollo de Habilidades Communicativas is described. Then five studies carried out with the instrument are presented. In the first study vocabulary development of Spanish-speaking infants and toddlers is compared to that of English-speaking infants and toddlers. The English data were gathered using a comparable parental report, the MacArthur Communicative Development Inventories. In the second study the general characteristics of Spanish language acquisition, and the effects of various demographic factors on that process, are examined. Study 3 examines the differential effects of three methods of collecting the data (mail-in, personal interview, and clinic waiting room administration). Studies 4 and 5 document the reliability and validity of the instrument. Results show that the trajectories of development are very similar for Spanish- and English-speaking children in this age range, that children from varying social groups develop similarly, and that mail-in and personal interview administration techniques produce comparable results. Inventories administered in a medical clinic waiting room, on the other hand, produced lower estimates of toddler vocabulary than the other two models.

Narrative Discourse in Children with Early Focal Brain Injury

Children with early brain damage, unlike adult stroke victims, often go on to develop nearly normal language. However, the route and extent of their linguistic development are still unclear, as is the relationship between lesion site and patterns of delay and recovery. Here we address these questions by examining narratives from children with early brain damage. Thirty children (ages 3:7-10:10) with pre- or perinatal unilateral focal brain damage and their matched controls participated in a storytelling task. Analyses focused on linguistic proficiency and narrative competence. Overall, children with brain damage scored significantly lower than their age-matched controls on both linguistic (morphological and syntactic) indices and those targeting broader narrative qualities. Rather than indicating that children with brain damage fully catch up, these data suggest that deficits in linguistic abilities reassert themselves as children face new linguistic challenges. Interestingly, after age 5, site of lesion does not appear to be a significant factor and the delays we have witnessed do not map onto the lesion profiles observed in adults with analogous brain injuries.

Constraints on plasticity in a connectionist model of the english past tense

This paper investigates constraints on dissociation and plasticity in a connectionist model undergoing random lesions both prior to and during training. When networks were trained only on phonological encodings of stem-suhed pairs similar to English regular verbs (e.g., walk walked), long-term deficits (i.e., critical period effects) were not observed, yet there were substantive short-term effects of injury. When training vocabulary reflected the English-like competition between regular (suffixed) and irregular verbs (e.g., go went, hit hit), the acquisition of regular verbs became increasingly susceptible to injury, while the irregulars were learned quickly and were relatively impervious to damage. Patterns of generalization to novel forms conflicts with the assumption that this behavioral dissociation is indicative of selective impairment of the learning and generalization of the past tense rule, while the associative lexical-based mechanism is left intact. Instead, we propose a view of network performance in which the regular-irregular dissociation derives from a general reduction in the ability to find a single-mechanism solution when resolving the competition between two classes of mappings. In light of other models in which regular and irregular forms compete (e.g., Patterson, Seidenberg, & McClelland, 1989), as well as patterns of performance in normal and disordered English speakers (e.g., Pinker, 1991), two general implications are discussed: (1) critical period effects need not derive from endog-enously determined maturational change, but instead may in part result from learning history in relation to characteristics of the language to be learned (i.e., entrenchment), and (2) selective dissociations can result from general damage in systems that are not modularized in terms of rule-based vs. associative mechanisms.

How vocabulary size in two languages relates to efficiency in spoken word recognition by young Spanish-English bilinguals*

Research using online comprehension measures with monolingual children shows that speed and accuracy of spoken word recognition are correlated with lexical development. Here we examined speech processing efficiency in relation to vocabulary development in bilingual children learning both Spanish and English (n=26 ; 2 ; 6). Between-language associations were weak: vocabulary size in Spanish was uncorrelated with vocabulary in English, and childrens facility in online comprehension in Spanish was unrelated to their facility in English. Instead, efficiency of online processing in one language was significantly related to vocabulary size in that language, after controlling for processing speed and vocabulary size in the other language. These links between efficiency of lexical access and vocabulary knowledge in bilinguals parallel those previously reported for Spanish and English monolinguals, suggesting that childrens ability to abstract information from the input in building a working lexicon relates fundamentally to mechanisms underlying the construction of language.

Children's Productivity in the English Past Tense: The Role of Frequency, Phonology, and Neighborhood Structure

The productive use of English past tense morphology in school-aged children (N= 74; 3 years, 8 months to 13 years, 5 months) is explored using on elicited production task. Errors represented 20% of the responses overall. Virtually all of the children demonstrated productivity with regular (e.g., good) and irregular patterns (zero-marking, e.g., sit + sit; vowel-change, e.g., ride -+ rid). Overall frequency of errors decreased with age, yet the tendency for certain types of irregularizations increased in the older groups. Analyses across items indicated that all error types were predicted by combinations of item frequency, phonological chamcteristics of stems and past tense forms, and aspects of phonological past tense “neighborhoods.” Contrary to “hybrid” or dual-mechanism models incorporating a phonologically-insensitive default mechanism (e.g., Prasada & Pinker, 1993), these results suggest that children’s productivity with regular and irregular patterns is consistent with a phonologically-based constraint satisfaction system similar to that implemented in connectionist models (Daugherty & Seidenberg, 1992; Plunkett 81 Marchman, 1991,1993).

Production of complex syntax in normal ageing and alzheimer's disease

Abstract Word-finding difficulties are among the earliest symptoms of Alzheimers disease (AD), but most AD patients retain the ability to produce well-formed sentences until the late stages of their disease. This dissociation has been used to argue for a modular distinction between grammar and the lexicon. In this paper, we offer an alternative view. First, we show that grammatical production is impaired in AD patients when grammar is assessed under highly constrained conditions in a film description task. Furthermore, these grammatical deficits are comparable in some respects to the patterns of lexical impairment observed in this and other studies of AD; specifically, patients do not produce frank lexical or grammatical errors, but they do find it difficult to access the “best fit” between meaning and form. We propose that differences in the onset time for lexical and grammatical symptoms in AD are due not to a disconnection between modules, but to fundamental differences in the automaticity and/or acce...