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| Study | Participants | Materials | Results |
| 1. | | 12 GreekDS (CA: 6 - 7.11 years)/12 Greek DS adolescents (CA: 14 - 15.11 years)/12 Greek TDC (CA: 6 - 7.11 years) | Psychometric Criterion of Language Adequacy: a) test of Morphosyntactic Comprehension; b) test of Morphosyntactic Production | Children with DS: significant lower scores than adolescents with DS and TDC in receptive syntax tasks, but no differences from adolescents with DS in expressive syntax tasks. Most errors made of DS individuals concerned the verb morpheme production. Syntactic development in DS continues to grow in adolescence, especially in the expressive domain. |
| 2. | | 14 Italian DS (mean CA: 54 months, mean DA: 34 months)/14 Italian TDC (mean CA: 29 months, mean DA 38 months) | PiNG Italian MB-CDI | DS: general weakness in lexical comprehension and production. Significantly higher percentage of errors than TD, as well as no-responses. Also, more representational gestures + more unimodal gestural answers. Nouns are understood and produced in higher percentages than predicates. |
| 3. | | 24 English DS (mean CA: 11.1 years, VCA 2.5 - 5.2)/24 TD (mean CA: 3.0 years, VCA 2.5 - 5.2) matched on verbal comprehension | Comprehension task of active/passive/neutral sentences | Better performance on active sentences than on passive for both groups. Also, similarities in terms of percentage correct responses and patterns of errors. DS: a slight delay (6 - 12 months) in the appearance of syntactic strategies of comprehension compared with those non-retarded children. |
| 4. | | 16 Italian DS (CA: 6.7 - 14.2 years)/16 with SLI (CA: 3.5 - 5.7 years)/32 TDC (CA: 3.8 - 5.7 years) | Stanford-Binet Scale Leiter PPVT Boston Naming Test (BNT) Linguistic Comprehension Test (LCT) Phrase Repetition Test (PRT) | DS + SLI: worse performance than TD. Although no significant differences in lexical and morphosyntactic comprehension abilities, significant differences did emerge in morphosyntactic production capacities. DS: more errors than SLI children, who, in turn, made more errors than TDC. DS: more omissions, a significantly higher number of articles, verbs, and prepositions than SLI children, whereas no difference was found for nouns and for modifiers. DS + SLI (but not with TD) omitted more articles in sentences than in syntagms. Qualitative analysis of the morphosyntactic errors revealed strong similarities between the DS + TD groups. |
| 5. | | 20 American DS (CA: 12 - 21 years)/16 with cognitive impairment of unknown origin (CA: 12 - 21 years) | 3-hour protocol: hearing screening, the Bead Memory and Pattern Analysis subtests of the Stanford Binet, PPVT-3, the vocabulary subtest of the Test of Auditory Comprehension of Language-3, interview language samples, narrative language samples, Kaufman-ABC number recall task (digit span) and the Nonword Repetition Test | DS: The auditory-verbal working memory deficit appears to be part of its specific phenotype, as well as the loss of comprehension skills in adolescence, and is poorer for both syntax comprehension and vocabulary comprehension than the group with cognitive impairment of unknown origin. The significantly better performance of the DS and cognitively impaired groups on the PPVT-3, relative to syntax comprehension, appeared attributable to CA and the additional life experience. Deficits in auditory-verbal working memory, syntax and vocabulary comprehension, and narration of picture-books without an opportunity to preview them are all specific to the adolescent group with DS. |