Effect of Vowel Context and Phoneme Position on Correct Articulation of Phonemes in Malayalam Speaking Children with Down Syndrome: A Pre Post Therapy Comparison

Abstract

Evidence on contextual coarticulatory facilitation of speech sound production is valuable for speech correction and is documented as single case studies on a number of phonemes in the past, majorly in English, and scanty in Indian languages. As the facilitating influence of vowels on consonant production varies across languages, such contexts need to be established and validated in different languages and clinical populations with speech sound errors. In spite of having good language abilities, reduced speech intelligibility interferes with the communication efficiency of individuals with Down syndrome (DS). Speech intelligibility of children with DS improves with intervention even though the learning pace is slow. Hence it is necessary to establish facilitating vowel contexts and phoneme positions to ensure faster improvement in this population. The present investigation was designed as a single subject study to establish facilitating vowel contexts and phoneme positions in the correct production of phonemes by children with DS in Malayalam. Fifteen Malayalam speaking children with DS in the age range of 7-13 years served as participants of the study. Ten frequently misarticulated phonemes in Malayalam were selected for articulatory intervention which included unvoiced retroflex stop /ʈ/ (4 participants), voiced retroflex stop /ɖ/ (4 participants), retroflex nasal /ɳ/ (5 participants), retroflex lateral /ɭ/ (5 participants), unvoiced velar stop /k/ (1 participant), alveolar fricative /s/ (3 participants), retroflex fricative /ʂ/ (3 participants), alveolar tap /r/ (2 participants), alveolar trill /ṛ/ (1 participant) and retroflex approximant /ʐ/ (2 participants). Two wordlists with the target phonemes occurring in the context of various vowels in initial and medial positions were prepared for assessment and intervention. Assessment wordlist was used for obtaining baselines and intervention wordlist was used as stimuli for therapy. Verbal imitation task was employed for elicitation of responses. For each phoneme, participants received a maximum of 10 sessions of therapy, determined based on a pilot study. Participants received a total of 340 articulation therapy sessions using phonetic placement approach (Van Riper, 1972). Percentage of correct production was computed for each context across sessions and the data was represented graphically. A pre-post therapy comparison was done using Wilcoxon signed rank test. However, no significant difference was seen in spite of higher post therapy scores in multiple contexts. As applying statistical analysis could not explain the findings of the present study appropriately, the data was analysed qualitatively using graphical representations. Three measures, Minimum Number of Sessions for Correct Production (MNS-CP), Minimum Number of Sessions for Consistent Correct Production (MNS-CCP) and Total Number of Sessions with Correct Production (TNS-CP) were computed from the graphs to address the objectives of the study. Findings revealed a definite effect of vowel context and phoneme position on correct production of phonemes in children with DS. Facilitating vowel contexts identified were high back vowel /u/ for /ʈ/, /ɳ/, /ɭ/ and /ʐ/, mid back vowel /o/ for /ɖ/, /ṛ/ and /ʂ/, high front vowel /i/ for /s/ and /r/. Consonant /k/ was favoured by multiple vowel contexts; /a/, /u/ and /o/. Initial position facilitated the production of four phonemes (/ɖ, s, ʂ, k/) and medial position favoured three phonemes (/ʈ, r, ṛ/). The findings of the present study can be adapted for assessment and intervention of speech sound errors in children with DS in Malayalam. For practicing speech language pathologists, these established facilitating contexts will serve as a quick reference guide to save significant time and effort involved in the speech correction process.