Links between the mastery of complex syntax and more general cognitive abilities (e.g., working memory [WM] and attention) are widely reported for both typically developing children and children with atypical language development, such as developmental language disorder (DLD). These observations have resulted in debates about whether the locus of breakdown in populations with known syntactic impairment is situated in a specific language system or a more general cognitive system. Recently, a hybrid model of language acquisition, the Parallel Combination Approach (PCA), in which both domain-specific and domain-general processes contribute to language development, was put forward.
Our review, which is the first to examine the validity of the PCA, compares a body of our own work investigating the language-cognition interface in various populations: children with specific learning difficulties (SLD), attention deficit hyperactivity disorder (ADHD) and DLD. We report findings from two cross-sectional studies (Studies 1 and 2), one priming study (Study 3) and two training studies (Studies 4 and 5). The results confirm a close link between WM, attention, and syntax, in line with domain-general approaches to language impairment. However, certain findings within this review also reveal that impaired general skills can be found alongside intact syntax, providing support for domain-specific approaches. While these results may initially appear contradictory, we argue that they are perfectly in line with the predictions made by the PCA.
Study 1confirms that clinicians should assess syntax in children with SLD to avoid the missed diagnosis of comorbid DLD. Studies 2-3 offer perspectives on the differential diagnosis of ADHD and DLD and highlight the advantages of using probe tests and dynamic assessment when evaluating children with suspected syntactic impairment. Studies 4-5 describe a novel, empirically validated WM training program that has been shown to lead to syntactic improvements on clinical markers of DLD. Finally, the PCA is also clinically relevant as it underscores that children with the same diagnostic label can present dissimilar cognitive profiles with different sources of breakdown. Collectively, The various studies highlight the intricacy of the relationship between syntax and cognition, which cannot be easily described by traditional single-disciplinary frameworks.

S. Karger AG, Basel.