Background: Autism spectrum disorder (ASD) and social pragmatic communication disorder (SPCD) are two neurodevelopmental disorders with many similarities in affected individuals' impairments in social-communicative and pragmatic development. A central question pertaining to their differentiation concerns whether the distinction is truly qualitative or, instead, quantitative in nature, and indeed, defining the boundary between SPCD and ASD with IQ in the normal range often presents differential-diagnostic difficulties. While deficits in the comprehension of certain linguistically systematic implicit verbal meanings have been targeted by experimental research in ASD, to date they have not been investigated in controlled experiments in SPCD.
Aims:The empirical objectives of our study are twofold. First, it is explored whether the comprehension of a set of highly systematic, grammaticalized implicit meanings is impaired in ASD and SPCD children compared to their typically developing (TD) peers, and whether ASD and SPCD children differ from each other in accessing these verbal meanings. Second, it is investigated whether receptive grammatical competence and first-order ToM abilities are associated with children's performance in any way and whether there is a difference in this regard between the ASD and the SPCD group. Methods & Procedures: Our main experiment, using a sentence-picture verification task, tested the comprehension of highly systematic implicit verbal meanings, including grammaticalized implicatures, presuppositions, and entailments.The experiment was complemented with a false-belief (ToM) task and a test of receptive grammar, among other measures. Seventy-one 4-to-9-year-old children participated in the study (ASD: n=19, SPCD: n=13, TD controls: n=39).Outcomes & Results: While both children with SPCD and children with ASD performed significantly more poorly than the TD group, only the comprehension profile of the SPCD group differed significantly from that of the TD group. Importantly, while ASDs' performance exhibited an association with their ToM results,This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.