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CONSONANT CLUSTERS IN DISORDERED L1 ACQUISITION: A LONGITUDINAL ACOUSTIC STUDY

We report a longitudinal instrumental study of the acquisition of English wordinitial consonant clusters by children with phonological disorders. Interim results pertaining to /VW/ are given for four children with phonological disorders and two normally-developing children. Duration measures show that before the successful acquisition of /VW/, the stop closure is similar to that of the independent stops, but after, the stop closure duration for /VW/ is shorter than for /W/ or /G/. INTRODUCTION This longitudinal instrumental acoustic study is motivated by the relative paucity of detailed quantitative information about the phonetic strategies used in the acquisition of consonant clusters by speech-disordered children. Most analyses of cluster acquisition in normal and disordered speech are transcriptionbased. It is essential to explore both these aspects of the acquisition of phonological contrast. The developmental maturation of a speaker’s ability to render adultlike phonetic encodings of a contrast, and the perceptual discontinuity at which the speech community (or phonetician) judges a contrast to be successfully acquired are separate processes. Macken and Barton [1], for example, show that in the acquisition of the stopvoicing contrast, differences in VOT which are imperceptible to adult listeners are produced by some children. Such ‘covert contrast’ has also been demonstrated in [2,3,4]. The children then proceed to the production of an acceptable contrast, though initially it is not adultlike. Applying these findings to consonant cluster acquisition, we might expect a stage of covert contrast in which the phonological contrast between cluster and singleton is expressed phonetically in a manner which can be detected instrumentally but is effectively imperceptible. Weismer [4] discusses a case in which, for example, [W] realising reduced /VW/ has greater closure duration than [W] realising /W/. We would also expect to observe the gradual approximation of the child to the adult model. The detection of covert contrast and the discovery of the ways in which children approach phonetically mature expressions of contrast would have important clinical implications [2]. The results presented here are taken from a larger study which will be able to explore the issues raised in greater depth. METHODOLOGY The four experimental subjects DB (4;1), SR (5;7), KG (4;1) and IB (4;3) were from the Edinburgh area, speaking varieties of Scottish English. The subjects were the age indicated at the start of the study. All exhibited functional cluster reduction of /VW/ to [G] or [W], although subject KG had resolved already by the first session. All were undergoing courses of speech and language therapy having been diagnosed as phonologically disordered. In addition, we refer to two normally-developing children, RM (4;0) and JS (3;3). The children uttered nine target words (forming minimal triples, Table 1) in a naturalistic manner as part of a series of ten picture-naming games, each game comprising three dissimilar targets from a larger dataset. No minimal pairs appeared in the same game. The carrier phrase was ‘give me x (please)’. Table 1. Coronal targets.