The authors asked whether there is evidence to support the existence of the vocabulary spurt, an increase in the rate of word learning that is thought to occur during the 2nd year of life. Using longitudinal data from 38 children, they modeled the rate of word learning with two functions, one with an inflection point (logistic), which would indicate a spurt, and one without an inflection point (quadratic). Comparing the fits of these two functions using likelihood ratios, they found that just 5 children had a better logistic fit, which indicated that these children underwent a spurt. The implications for theories of cognitive and language development are considered.

This article tests the hypothesis that young children have a maturational difficulty with A-chain formation that makes them unable to represent unaccusative verbs in an adultlike fashion. We report the results of a test of children's performance on the genitive-of-negation construction in Russian, which, for adults, is an ''unaccusativity diagnostic,'' since genitive case is allowed to appear on the underlying direct object argument of unaccusatives as well as on direct objects of standard transitive verbs within the scope of negation. We show that although Russian children know the properties of the construction, they have notable difficulty using it with unaccusative verbs. Since the input evidence for genitive of negation with unaccusative verbs is quite robust, we interpret our results as support for the hypothesis.Studies of early language acquisition help us understand the biological roots of language. For example, the growing body of work that reveals extremely early knowledge of many properties of language (e.g., Wexler 1996, Crain and Thornton 1998, and references therein) is particularly interesting in light of debates over the ''poverty of the stimulus'' and the nature of Universal Sergey Avrutin conducted an informal pilot experiment for the project reported here and participated in the earliest discussion of this work. We wish to thank him for his invaluable assistance and encouragement. Ron Fein collected preliminary data relevant to our experiment and was an active participant in the early stages of this work. We are grateful for his contributions to this project. Marina Shatskaya and Alexei Semenov persuaded the directors of two Moscow kindergartens to let us conduct our experiment on their premises. We are grateful to them for their energetic efforts on our behalf; we are also grateful to the staff of these kindergartens for their helpfulness and good-natured tolerance of the disruptions we caused. For helpful advice and discussion, we wish to thank Hagit Borer,

This paper describes the Pittsburgh Registry of Infant Multiplets (PRIM; Pittsburgh, Pennsylvania), the results of pilot research conducted in this registry, and the plans for future studies. The main focus of the registry is on psychological development and the risk for behavioral disorders. Particularly, characteristics associated with antisociality and the risk for substance use disorders (e.g., aggressivity, hyperactiv-ity/impulsivity), as well as language development and other traits (e.g., dental health) are among the research targets.

T his paper describes the Pittsburgh Registry of Infant Multiplets (PRIM; Pittsburgh, Pennsylvania), the results of pilot research conducted in this registry, and the plans for future studies. The main focus of the registry is on psychological development and the risk for behavioral disorders. Particularly, characteristics associated with antisociality and the risk for substance use disorders (e.g., aggressivity, hyperactivity/impulsivity), as well as language development and other traits (e.g., dental health) are among the research targets.

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