In this note we discuss pMLU, a whole-word measure for phonological development that was proposed by Ingram (2002). Ingram's rules for calculating pMLU are analysed and we point at the crucial role of the level of transcription for making pMLU measurements comparable over different corpora. The main aim of the paper is an assessment of the reliability and the validity of pMLU. The assessment is accomplished using a computational tool for measuring pMLU on two large Dutch CHILDES corpora. We propose minimal sample sizes for reliable measurements relative to the stage of phonological development.

A longitudinal analysis is presented of the fillers of a Dutch-speaking child between 1.10 and 2.7. Our analysis corroborates familiar regularities reported in the literature: most fillers resemble articles in shape and distribution, and are affected by rhythmic and positional constraints. A novel finding is the impact of the lexical environment: particular function words act as 'anchor' words that attract occurrences of schwa fillers after them. The child inserts significantly more schwa fillers in these contexts. The anchor words are among the most frequent words preceding articles in the input, indicating a sharp sensitivity to such distributional regularities. Nasal fillers too are affected by distributional learning, but at the phonological level: the child first uses nasals before [h]-initial nouns, and then generalizes this usage to all [h]-initial words. These observations are related to the growing body of evidence for the impact of distributional learning on early language production.

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Fikkert (1994) analyzed a large corpus of Dutch children's early language production, and found that they often add targetless syllables to their words in order to create bisyllabic feet. In this note we point out a methodological problem with that analysis: in an important number of cases, epenthetic vowels occur at places where grammatical morphemes (e.g. plural and diminutive suffixes) may be expected. Hence, the seemingly targetless syllables may represent grammatical morphemes. A reanalysis of Fikkert's original data reveals that her rhythmic explanation cannot be maintained if those cases are excluded from the analysis.

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