Aims: Using electropalatography (EPG), a few case studies have reported observations of increased tongue-palate contact for perceptually acceptable fricatives and alveolar stops produced by children with speech sound disorder of unknown origin (SSD). This study aimed to further investigate this issue by conducting quantitative analysis of amount of tongue-palate contact of alveolar stops produced by children with SSD that were perceived as correct productions. Their results were compared to those obtained from typically developing children.
Methods: This is a retrospective analysis of EPG data collected for two previous research projects. The participants included nine children with SSD – four boys and five girls, aged 8;06-16;00 years; and eight typically developing children – six boys and two girls, aged 4-12 years. The stimuli were alveolar stops /t/, /d/, and /n/, produced at word-initial, word-medial, or word-final positions (e.g., tea, mended, town). The alveolar stop segments were annotated and percent contact was measured at the frame of maximum contact for each production.
Results: The children with SSD showed significantly higher amount of tongue-palate contact than the typically developing children for /t/ and /d/. However, there was no significant difference in the amount of contact between the two groups for /n/. Visual examination of EPG contact patterns revealed that the children with SSD generally showed more contact in the posterior central area of the palate than the typically developing children.
Discussion and conclusion: The findings confirm previous observations that children with SSD tend to have increased tongue-palate contact even for speech sounds that were perceived as correct productions. The differential results for oral and nasal alveolar stops might be related to the fact that complete anterior and lateral closure is needed for building up intra-oral pressure during the oral stop production. The results have important clinical implication in terms of setting treatment targets for clients.