Lists of the first 50 words comprehended and produced by eight infants between o ; 9 and 1 ; 8 were compared. Comprehension development began earlier (around o ; 9) and reached the 50-word level (age 1 ; 1) earlier than production development (ages 1; o and 1; 6 respectively) and rate of word acquisition for comprehension was twice that of production, confirming the hypothesis that comprehension precedes production for lexical development. Word-class analysis revealed differences in the proportion and type of action words in comprehension and production vocabularies. It is suggested that action is central to lexical development but is expressed differently in comprehension, where action words are used to initiate actions, and production, where non-action words accompany the child's actions.

This study investigated the relationships between children's linguistic environments and their language acquisition. Speech samples taken from seven firstborn children and their mothers when the children were 1; 6 and 2 ; 3 were analysed within a number of semantic and syntactic categories to determine correlations between mothers' speech and subsequent language development. Several characteristics of mothers' speech (e.g. utterance length, use of pronouns) significantly predicted later child speech. The significant correlations suggested that mothers' choice of simple constructions facilitated language growth. Further, they showed that the motherese code differed from adult-adult speech in ways which aided language development. Differences between our study and previous investigations of environmental effects on language development probably resulted from the failure of earlier investigations to take into account children's level of language competence at the time when environmental effects were assessed.

A 50-utterance corpus for each of sixteen mothers during caretaking situations (diapering, dressing, bathing) was extracted from in-home tape recordings obtained over a three-day period. The children ranged from 1; 3.15 to 1; 7 and were classified according to Nelson's referentialexpressive distinction. A coding scheme consisting of three categoriescommunicative intent, focus of attention and evaluation -was employed to characterize the mothers' speech. Mothers of referential children produced a greater number of utterances per caretaking incident, more description and less prescriptives than did mothers of expressive children. The findings suggest that Nelson's referential-expressive distinction in child's speech is related to differences in mothers' pragmatic speech characteristics.

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