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Speech sound development in typically developing 2-7-year-old Dutch-speaking children: A normative cross-sectional study.

BACKGROUND
Dutch is a West-Germanic language spoken natively by around 24 million speakers. Although studies on typical Dutch speech sound development have been conducted, norms for phonetic and phonological characteristics of typical development in a large sample with a sufficient age range are lacking.


AIM
To give a detailed description of the speech sound development of typically developing Dutch-speaking children from 2 to 7 years.


METHODS & PROCEDURES
A total of 1503 typically developing children evenly distributed across the age range of 2;0-6;11 years participated in this normative cross-sectional study. The picture-naming task of the Computer Articulation Instrument (CAI) was used to collect speech samples. Speech development was described in terms of (1) percentage consonants correct-revised (PCC-R) and percentage vowels correct (PVC); (2) consonant, vowel and syllabic structure inventories; (3) degrees of complexity (phonemic feature hierarchy); and (4) phonological processes.


OUTCOMES & RESULTS
A two-way mixed analysis of variance (ANOVA) confirmed a significant increase in the number of PCC-R and PVC between the ages of 2;0 and 6;11 years (p < 0.001). The consonant inventory was found to be complete at 3;7 years of age for the syllable-initial consonants, with the exception of the voiced fricatives /v/ and /z/, and the liquid /r/. All syllable-final consonants were acquired before age 4;4 years. At age 3;4 years, all children had acquired a complete vowel inventory, and at age 4;7 years they produced most syllable structures correctly, albeit that the syllable structure CCVCC was still developing. All phonological contrasts were produced correctly at 3;8 years of age. Children in the younger age groups used more phonological simplification processes than the older children, and by age 4;4 years, all had disappeared, except for the initial cluster reduction from three to two consonants and the final cluster reduction from two to one consonant.


CONCLUSIONS & IMPLICATIONS
This paper describes a large normative cross-sectional study of Dutch speech sound development which, in clinical practice, can help Dutch speech-language pathologists to differentiate children with delayed or disordered speech development from typically developing children. What this paper adds What is already known on this subject In recent years many studies have been conducted worldwide to investigate speech sound development in different languages, including several that explored the typical speech sound development of Dutch-speaking children, but none of these latter studies explored both phonetic and phonological progress within a comprehensive age range and a large sample that is representative of the Dutch population. What this study adds to existing knowledge This study serves to fill this gap by providing normative cross-sectional results obtained in 1503 typically developing Dutch-speaking children aged between 2;0 and 6;11 years on informative parameters of speech development: PCC-R and PVC, consonant, vowel and syllabic structure inventories, degrees of complexity (phonemic feature hierarchy), and phonological simplification processes. What are the potential or actual clinical implications of this work? The detailed description of typical Dutch speech sound development provides speech-language pathologists with pertinent information to determine whether a child's speech development progresses typically or is delayed or disordered.