The comprehension of grammaticalized implicit meanings in SPCD and ASD children: A comparative study

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.

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.

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).

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, the performance of SPCDs showed a correlation with their receptive grammar skills. By contrast, the performance of TDs correlated with neither.

These findings reveal potential divergences in the cognitive developmental mechanisms that underlie the semantic-pragmatic difficulties in the two clinical groups, suggesting that the communicative impairments in ASD and in SPCD differ qualitatively, rather than quantitatively. Specific implications for theories of pragmatic impairments in ASD and in SPCD are discussed.

What is already known on the subject Linguistically systematic implicit meanings are understudied both in ASD and in SPCD. Within this domain of verbal meaning, the majority of relevant experimental work on ASD, concentrated on generalized (mostly: scalar) implicatures, has yielded somewhat divergent results, while the comprehension difficulties in SPCD have remained barely charted territory. Linguistically more highly conventionalized implicit verbal meanings have not been experimentally investigated in either neurodevelopmental disorder. What this study adds A primary finding of our study is that although both the SPCD and the ASD group show significant deficit in the comprehension of highly conventional, grammaticalized implicit meanings, SPCD children may diverge more in their comprehension profile from their TD peers than ASD children. Another key result is that the comprehension of grammaticalized implicit meanings is linked with different cognitive functions in ASD and in SPCD. While comprehension performance is associated with ToM in ASD but not in SPCD or in TD, it is correlated with receptive grammar skills in SPCD but not in ASD or in TD. Clinical implications of this study These findings provide potential support for the hypothesis that the difference between ASD and SPCD is qualitative rather than quantitative in nature, thereby casting doubt on the conception that pragmatic limitations in SPCD are to be approached as a less severe form of similar deficits in ASD. Uncovering differences in the underlying cognitive sources and in the comprehension deficits of children with ASD and SPCD are critical for the improvement of the accuracy of SPCD children's early diagnosis and timely therapeutic intervention.