Early Talkers and Late Talkers Know Nouns that License Different Word Learning Biases

Early Talkers and Late Talkers Know Nouns that License Different Word Learning Biases Eliana Colunga (eliana.colunga@colorado.edu) Department of Psychology and Neuroscience, 345 UCB Boulder, CO 80309-0345 USA Clare E. Sims (clare.holtpatrick@colorado.edu) Department of Psychology and Neuroscience, 345 UCB Boulder, CO 80309-0345 USA Abstract In typical development, word learning goes from slow and laborious to fast and seemingly effortless. Typically developing 2-year-olds are so skilled at learning noun categories that they seem to intuit the whole range of things in the category from hearing a single instance named – they are biased learners. This is not the case for children below the 20 th percentile on productive vocabulary (late talkers). This paper looks at the vocabulary composition of age-matched 18-30-month-old late- and early-talking children. The results of Experiment 1 show that late talkers’ vocabularies are more variable than early talker’s vocabularies. Crucially, Experiment 2 shows that neural networks trained on the vocabularies of individual late talkers learn qualitatively different biases than those trained on early talker vocabularies. These simulations make testable predictions for world learning biases of late- vs. early-talking children. The implications for diagnosis and intervention are discussed. Keywords: Late talkers; early talkers; computational models; neural networks, vocabulary composition. Introduction There is extraordinary variability in the vocabularies of very young children. A two-year-old in the lower 10 th percentile may produce around 10 words whereas a two- year-old in the top 10 th percentile will produce well over 300 (Fenson, Dale, Reznick, Thal, Bates, Hartung, Pethick, & Reilly, 1993). In general, the course of word learning proceeds from slow, effortful learning of nouns and of the range of things that belong in a category, to very rapid learning of object names. Indeed, typically developing 2- year-olds are so skilled at learning new nouns that they seem to intuit the whole range of things in a named category from a single naming experience. This is not necessarily the case for children below the 15 th -20 th percentile on productive vocabulary, or late talkers. Why do some children learn words quickly and early and others learn words slowly, maybe even showing effects that persist into adolescence? This paper looks at two possible contributing, and interrelated, factors: noun vocabulary composition and word learning biases. The evidence suggests that children become skilled noun learners, at least in part, because they know about the different kinds of properties that are relevant for categorizing different kinds of things. In the Novel Noun Generalization task (NNG), typically-developing children show word learning biases that are specific to different kinds: they generalize names for solid objects by shape and names for non-solid substances by material (e.g., Jones, Smith & Landau, 1991; Soja, Carey, & Spelke, 1991). The evidence also suggests that children learn how to learn nouns – and specifically learn how different kinds of properties are relevant for different kinds of things – as a consequence of learning names for things. Each noun the child learns appears to teach the child something general about how to learn new nouns that name things of that same kind, and critically, at the same time, this learned general knowledge constrains and facilitates the types of nouns the child will learn next. To the extent that this interrelation holds true for children in different ends of the language spectrum – late talkers and early talkers – one might be able to leverage this process to predict outcome. The first step, however, is to show that 1) late talkers and early talkers know different sorts of nouns and 2) that these differences in vocabulary structure lead to differences in word learning biases. This paper presents a first look at these questions by examining the noun vocabulary composition of 18-30- month-old late- and early-talking children and showing that neural networks trained on the vocabularies of individual late talkers learn qualitatively different biases than those trained on early talker vocabularies. Vocabulary composition and word learning biases The relationship between vocabulary composition and word learning biases has been typically characterized in one of two ways: abstract knowledge guides, facilitates and indeed allows word learning (e.g., Soja et al, 1991; Gelman & Bloom, 2000) or the words that have been learned give rise to, create, and in fact constitute generalized knowledge about word learning (e.g., Colunga & Smith, 2005, Samuelson, 2008). We would like to bypass the debate on whether word-learning biases are the egg to the vocabulary chicken or the other way around and focus instead on the interrelationship between these two factors. In the domain of names for objects and substances, and in typical development, vocabulary structure and abstract knowledge in the form of kind-specific generalizations appear to be tightly coupled. First, the tendency to attend to shape in the specific context of naming artifacts emerges as