Philip S. Dale

Variability in Early Communicative Development.

Data from parent reports on 1,803 children--derived from a normative study of the MacArthur Communicative Development Inventories (CDIs)--are used to describe the typical course and the extent of variability in major features of communicative development between 8 and 30 months of age. The two instruments, one designed for 8-16-month-old infants, the other for 16-30-month-old toddlers, are both reliable and valid, confirming the value of parent reports that are based on contemporary behavior and a recognition format. Growth trends are described for children scoring at the 10th-, 25th-, 50th-, 75th-, and 90th-percentile levels on receptive and expressive vocabulary, actions and gestures, and a number of aspects of morphology and syntax. Extensive variability exists in the rate of lexical, gestural, and grammatical development. The wide variability across children in the time of onset and course of acquisition of these skills challenges the meaningfulness of the concept of the modal child. At the same time, moderate to high intercorrelations are found among the different skills both concurrently and predictively (across a 6-month period). Sex differences consistently favor females; however, these are very small, typically accounting for 1%-2% of the variance. The effects of SES and birth order are even smaller within this age range. The inventories offer objective criteria for defining typicality and exceptionality, and their cost effectiveness facilitates the aggregation of large data sets needed to address many issues of contemporary theoretical interest. The present data also offer unusually detailed information on the course of development of individual lexical, gestural, and grammatical items and features. Adaptations of the CDIs to other languages have opened new possibilities for cross-linguistic explorations of sequence, rate, and variability of communicative development.

Short-form versions of the MacArthur Communicative Development Inventories

The MacArthur Communicative Development Inventories (CDIs) are a pair of widely used parent-report instruments for assessing communicative skills in infants and toddlers. This report describes short-form versions of the CDIs and their development, summarizes newly available normative data and psychometric properties of the instruments, and discusses research and clinical applications. The infant short form (Level I, for 8- to 18-month-olds) contains an 89-word checklist for vocabulary comprehension and production. The two parallel versions of the toddler short form (Level II, Forms A and B, for 16- to 30-month-olds) each contain a 100-word vocabulary production checklist and a question about word combinations. The forms may also be useful with developmentally delayed children beyond the specified age ranges. Copies of the short forms and the normative tables appear in the appendices.

Lexical development norms for young children

Developmental norms for young children’s vocabularies have a number of applications in research design, assessment, and intervention, but have previously been very difficult to obtain. In the present study, month-by-month norms for comprehension and production of 396 words from 8 to 16 months, and production of 680 words from 16 to 30 months, were derived from a norming study of 1,789 children between the ages of 8 and 30 months using the MacArthur Communicative Development Inventories (Fenson et al., 1993). The norms are available in the form of a database program, LEX, for MS-DOS-based computers.

Does frequency count? Parental input and the acquisition of vocabulary

Studies examining factors that influence when words are learned typically investigate one lexical category or a small set of words. We provide the first evaluation of the relation between input frequency and age of acquisition for a large sample of words. The MacArthur-Bates Communicative Development Inventory provides norming data on age of acquisition for 562 individual words collected from the parents of children aged 0 ; 8 to 2 ; 6. The CHILDES database provides estimates of frequency with which parents use these words with their children (age: 0 ; 7-7 ; 5; mean age: 36 months). For production, across all words higher parental frequency is associated with later acquisition. Within lexical categories, however, higher frequency is related to earlier acquisition. For comprehension, parental frequency correlates significantly with the age of acquisition only for common nouns. Frequency effects change with development. Thus, frequency impacts vocabulary acquisition in a complex interaction with category, modality and developmental stage.

Enhancing Linguistic Performance: Parents and Teachers as Book Reading Partners for Children with Language Delays.

In this study, we instructed parents and early childhood special education staff in Dialogic Reading, an interactive language facilitation technique. We compared the effects of this instruction on adult and child language during shared book reading and on childrens vocabulary growth in three different treatment conditions. Thirty-two children with language delays were randomly assigned to one of three groups: (a) parent instruction with one-on-one shared book reading practice, (b) staff instruction with one-on-one shared book reading practice, (c) staff instruction without one-on-one shared book reading practice (control group). Children were given standardized tests of vocabulary and were videotaped during shared book reading before and after the 8-week intervention period. Parents and staff showed changes in their shared book reading style consistent with the instruction they had received. After adult instruction in Dialogic Reading, children in all three groups spoke more, made longer utterances, produced more different words, and participated more in shared book reading. The magnitude of change in the childrens linguistic performance from pre- to posttest was positively correlated with the magnitude of change in adult behavior. There were no statistically significant changes in childrens vocabulary test scores. We interpret these findings as consistent with a Vygotskian model in which childrens linguistic performance can be enhanced by a supportive social context.

Genetic influence on language delay in two-year-old children

Previous work suggests that most clinically significant language difficulties in children do not result from acquired brain lesions or adverse environmental experiences but from genetic factors that presumably influence early brain development. We conducted the first twin study of language delay to evaluate whether genetic and environmental factors at the lower extreme of delayed language are different from those operating in the normal range. Vocabulary at age two was assessed for more than 3000 pairs of twins. Group differences heritability for the lowest 5% of subjects was estimated as 73% in model-fitting analyses, significantly greater than the individual differences heritability for the entire sample (25%). This supports the view of early language delay as a distinct disorder. Shared environment was only a quarter as important for the language-delayed sample (18%) as for the entire sample (69%).

Parent-Child Book Reading as an Intervention Technique for Young Children with Language Delays.

The effect of instructing parents of children with language delays in effective joint book-reading techniques was compared with language facilitation through more general conversational instruction. Thirty-three children, 3 to 6 years of age, and their mothers participated. Parents receiving a version of Whitehursts Dialogic Reading Training Program (Whitehurst et al., 1988) increased their use of what/who questions, open-ended questions, imitation, and expansions more than did parents receiving conversational language training. More modest effects were also found for the children, primarily in an increased rate of verbal responses to questions, increased number of different words, and increased Mean Length of Utterance. Parents whose behavior changed following the instruction were more likely to have had children whose language changed, a finding suggesting that the program affects childrens development. In addition, correlations between childrens pretest level and their change as a result of the treatment suggested that children learn different things from joint book reading at different points in development. On the whole, the results of this investigation of book-reading training suggest that it has considerable potential for facilitating language development with children with language delays, but that stronger interventions, monitored over a longer period of time, are needed.

Genetic Evidence for Bidirectional Effects of Early Lexical and Grammatical Development

This article addresses the autonomy hypothesis of vocabulary and grammar and bootstrapping mechanisms in early language development. Two birth cohorts of 1,505 and 1,049 same-sex twin pairs from the UK were assessed at 2 and 3 years on grammar and vocabulary, using adapted versions of the MacArthur Communicative Development Inventory. Vocabulary and grammar correlate strongly at both 2 and 3 years in both cohorts. Multivariate genetic modeling reveals a consistently high genetic correlation between vocabulary and grammar at 2 and 3 years. This finding suggests the same genetic influences operate for both vocabulary and grammar, a finding incompatible with traditional autonomy hypothesis, at least in early acquisition. Crosslagged longitudinal genetic models indicate both lexical and syntactical bootstrapping operate from 2 to 3 years.

Measuring Variability in Early Child Language: Don't Shoot the Messenger

Feldman et al. criticize the MacArthur Communicative Development Inventories (CDIs) as having too much variability, too little stability, and insufficient ability to predict early language delay. We present data showing that these characteristics of the CDI are authentic reflections of individual differences in early language development rather than measurement deficiencies. We also respond to their critical assertions concerning sociodemographic influences on the CDI scores.

Sex differences in early verbal and non‐verbal cognitive development

The present study of over 3000 2-year-old twin pairs used a sex-limitation model to examine genetic and environmental origins of sex differences in verbal and non-verbal cognitive ability. Girls scored significantly higher on both measures (p<0.0001), although gender only accounted for approximately 3% of the variance in verbal ability and 1% of the variance in non-verbal cognitive ability. For the verbal measure boys showed greater heritability than girls. Also the twin-pair correlation is significantly lower for opposite-sex twins than for non-identical same-sex twins. This indicates that individual differences in verbal ability include some sex-specific factors. Non-verbal cognitive ability did not differ in aetiology for boys and girls. We conclude that genetic and environmental influences differ for girls and boys for early verbal but not non-verbal development.