Speech production in people with Down syndrome
There is a well developed literature on the development of vocabulary and grammar in children with Down syndrome but limited information in the area of speech production. The spoken language of people with Down syndrome often leads to a lack of intelligibility which does not necessarily diminish with age, despite slow but steady development of phonology. This paper explores some of the elements in speech production which may contribute to the listeners' perception of reduced intelligibility in the speech of people with Down syndrome.
Down Syndrome Research and Practice (2008)
There is a general consensus that speech difficulties are common in individuals with Down syndrome and that these consist of a complex interweave of phonological and motor-speech delay and deviance. Phonological immaturities such as final consonant deletion, use of stops for fricatives, producing voiced for voiceless sounds and vice versa are common. Many studies have suggested the pattern of speech delay to be similar to that of young developmentally typical children. This may be an over-simplistic view of the situation. Roberts et al. found additional systematic errors not previously reported, for example palatal fronting, fricative simplification, deaffrication, and lateralisation of sibilants. Dodd and Thompson clearly show that children with Down syndrome are inconsistent in speech production, with over half of all words produced being pronounced differently on repeated productions. Variability is also reported in the articulation of fricatives by young people with Down syndrome.
Speech can be analysed in terms of its segmental structure (the precision and appropriateness of the sequences of sounds produced), or its suprasegmental aspects (intonation, rhythm, stress, voice). Studies undertaken by Bray and associates indicate that there may be suprasegmental differences which appear to be associated with problems of identifying and signalling word and phrase boundaries[6,7,8]. For some of the people with Down syndrome studied, word and phrase endings were better articulated and carried more stress than the initial syllable or the head of the tone group. This is contrary to typical speech in English where the first syllable in a disyllabic word and the initial sentence position carries the higher stress. Syllable deletion is common in the speech of people with Down syndrome and Heselwood, Bray and Crookston have suggested that syllable deletion allows for simplification of the rhythmic structure of the utterance, making the neurophysiological process of speaking easier. Links between production and perception need to be considered as Pettinato and Verhoeven show that perception of weak syllables is problematic in adolescents with Down syndrome.
Dysfluency (stuttering) is the inability to move forward in the utterance because of repetitions of
a sound, syllable or word, prolongations of sounds or of silence and tense pauses (both filled and
unfilled) associated often with obvious struggle to produce the word. The issue of whether the dysfluencies
of people with Down syndrome can be defined as stuttering is unresolved as the definition includes
more than just overt speech behaviours (levels of awareness, anxiety and avoidance form part of the
The literature on dysfluency in people with Down syndrome suggest a much higher incidence than in the general population (47% as against 1%[10,11]). Dysfluency can add to the lack of intelligibility in speakers and adds another level of difficulty in the production of speech by children with Down syndrome. Berstein Ratner suggests that, in typically developing children, dysfluency is related to language processing. As grammatical morphemes are rapidly expanding, children find the processing load significantly higher and a breakdown in fluency can result. Bray, in a study of two young dysfluent children with Down syndrome, found that the dysfluencies did not show a definite relationship to word finding problems and that the nature of the speech output consisted of 