Early lexical and syntactic development in Quebec French and English: implications for cross‐linguistic and bilingual assessment

Mean length of utterance (MLU) in morphemes was examined as a predictor of the grammatical complexity of natural language corpora of normal preschoolers and of children and adolescents with delayed language, Fragile X syndrome, Down syndrome, and autism. The Index of Productive Syntax (IPSyn) served as the measure of syntactic and morphological proficiency. For all groups, a strong curvilinear association between measures was found across the MLU range from 1.0 to about 4.5. Correlations were weaker when MLU exceeded 3.0 than during earlier stages of language development, however, confirming previous suggestions that MLU becomes less closely associated with grammatical development as linguistic proficiency increases. For the language-disordered groups, moreover, the curves relating the two measures differed from the curves for the normal preschoolers because MLU frequently overestimated actual IPSyn scores. The results are discussed with respect to the use of MLU in conjunction with other measures of syntactic complexity in the study of atypical language development.

One of the most widely used indices of language development is a measure of utterance length in morphemes (MLUm). This study examines the applicability of MLUm to the acquisition of Irish. MLUm was calculated for data from Cian, aged 1; 11-3; 0. Even when an attempt was made to 'assume the maximum' by counting all possible morphemes, the correlation between a morpheme MLU (MLUm) and a word count MLU (MLUw) was very high (0.99). This points to MLUw being as effective a measure of Irish development as MLUm, as well as being easier to apply and more reliable. MLUw was calculated for the two younger children in the study (Eibhlís 1; 4-2; 1 and Eoin 1; 10-2; 6). An examination of the relationship between the three children's MLUw values and their grammatical complexity as measured on ILARSP (the Irish adaptation of LARSP) indicates that MLUw is a useful preliminary index for early development in Irish. However, further data are necessary to check whether MLUw loses its predictive relationship with grammatical complexity after a certain point. The study emphasizes the caution necessary in applying MLU to languages whose acquisition has not hitherto been studied, and underlines the role of MLU as a preliminary measure, which must not be overinterpreted.