Difficulties in sounds and sentences: The relation between phonological and syntactic difficulties of toddlers with developmental language disorder
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For children with a developmental language disorder (DLD), impairments in phonology and syntax often co-occur (Fey et al., 1994; Tyler, Lewis, Haskill & Tolbert, 2002). However, it is not clear whether, and if so how, difficulties in these domains are related. The current study examines the relation between phonological and syntactic difficulties in 45 toddlers with DLD, aged between 2;4 and 4;3 (M = 3;6). It comprises a concurrent and longitudinal examination of receptive and expressive phonological and receptive and expressive syntactic abilities. Correlation analyses indicated that phonological and syntactic abilities of toddlers with DLD were related at concurrent time points within the receptive and expressive domain. Furthermore, repeated mixed effects analyses showed that improvement in expressive phonological abilities was related to improvement in expressive syntactic abilities, and that improvement in receptive phonological abilities was related to improvement in receptive syntactic abilities. Finally, a qualitative analysis was conducted to explore differences between toddlers with different phonological diagnoses. This analysis suggested that toddlers diagnosed with an inconsistent phonological disorder had poorer syntactic skills than toddlers diagnosed with a consistent phonological disorder, although further research is needed to address this issue. The results of the current study were used to compare four different theories on DLD, including the Bucket theory (Crystal, 1987), a grammatical theory (Rice, Wexler and Cleave, 1996), cascading theories (Chiat, 2001; Joanisse and Seidenberg, 1998), and implicit learning theories (Romberg & Saffran, 2019; Ullman & Pierpont, 2005). The results are mostly in agreement with the predictions made by the cascading and implicit learning theories. This study contributes to our understanding of how different components of language interact during the language development of children with DLD. More specifically, it provides insight into how receptive and expressive phonological skills are associated with syntactic comprehension and production skills in toddlers with DLD. This study could have implications for clinicians and speech and language pathologists, as the interactions across phonology and syntax could be used in future interventions for toddlers with DLD.