Language, literacy, and behaviour in children with a high-functioning autism spectrum disorder compared to children with specific language impairment, specific reading disorder, and typically developing peers

High-functioning Autism Spectrum Disorder (HFASD), Specific Language Impairment (SLI), and Specific Reading Disorder (SRD) are developmental disorders of genetic origin showing increased prevalence in first degree biological relatives. Communication deficits are requisite in HFASD while language or literacy or both are impaired within the SLI and SRD populations. All disorders typically impact adaptive functioning with psychopathology also reportedly elevated. Despite this, no research has simultaneously compared the development of young children with HFASD, SLI, or SRD to typically developing (TD) peers on language, literacy, and behaviour within the first few years of school. Based on a consideration of previous research two studies were conducted. A cross-sectional study investigated language, literacy, and behaviour across the HFASD, SLI, SRD, and TD populations. This revealed that HFASD children had average cognition, attention, visual memory, visual-perception, phonological awareness, phonological memory, rapid naming, semantics, syntax, and literacy with pragmatic skills severely delayed. Parent-reported internalising, externalising, and total psychopathology was in the borderline clinical range while adaptive behaviour was moderately delayed. Next, the predictors of literacy were investigated across the groups. FSIQ best predicted concurrent literacy for HFASD children followed by phonological processing and formal language. These predictors were most like those obtained for TD peers. Predictors were then utilised to ascertain the best model for each literacy measure for each participant group. Phonological processing explained the greatest amount of variance in concurrent literacy ability for all groups followed equally by visual-perception, semantics, and FSIQ. Last, within group heterogeneity was examined. Seventeen HFASD children presented with average language and literacy skills, 4 had above average abilities, while 9 had a SLI profile, 5 a SRD profile, and 4 a combined SLI-SRD profile. A second study examined the early developmental progression of language, literacy, and behaviour in HFASD children compared with SLI and TD peers. HFASD children had a developmental trajectory for non-verbal skills from Year Prep to Year 1 and for formal language and psychopathology from Year Prep until Year 3-4 often approximating that of TD peers. The developmental trajectory for pragmatics, reading, spelling, and adaptive behaviour from Year Prep until Year 3-4 however was more often different to that of TD peers. Compared with the SLI group HFASD children had a similar developmental trajectory for non-verbal, vocabulary, pragmatics, and reading skills but a different developmental trajectory for syntax, CELF-semantics, spelling, adaptive behaviour, and psychopathology. Next longitudinal literacy predictors were identified and literacy models developed. FSIQ was the best predictor of long-term literacy outcomes for HFASD children followed by phonological processing and formal language. FSIQ and phonological awareness were most frequently incorporated into final literacy models for the HFASD group. These results paralleled those found for TD but not SLI peers. Overall, this dissertation provided additional insight into the language, literacy, and behavioural presentation of young HFASD children compared with other groups with well-documented language or literacy deficits or both and TD peers. Some findings aligned with previous research whilst others contribute unique information to assist with the differentiation of HFASD, SLI, and SRD childre