An investigation of language abilities in individuals with high-functioning autism and asperger’s disorder

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Autism and Asperger’s disorder are complex neurodevelopmental disorders that share many clinical deficits in social, language, motor and behvioural symptoms (American Psychiatric Association, 2000; World Health Organization, 1992). Current diagnostic criteria differentiate the disorders on the basis of the presence (autism) or absence (Asperger’s disorder) of significant language delays prior to 3 years of age. There has been an ongoing debate regarding whether autism and Aspergers disorder (AD) are variants of a single condition, or should be considered as two distinct conditions with own set of symptoms (e.g. Allred, 2009; Bennett et al., 2008; Dickerson Mayes & Calhoun, 2001; Dickerson Mayes, Calhoun, & Crites, 2001; Howlin, 2003; Kamp-Becker et al., 2010; Macintosh & Dissanayake, 2004; Sanders, 2009; Volkmar, State, & Klin, 2009; Witwer & Lecavalier, 2008). In the absence of objective clinical markers to distinguish between the disorders, the next revision of the DSM (DSM 5) to be officially released in May 2013 will merge autism and AD into a single autism spectrum disorder (ASD) category. What is not in dispute is there are a sub-group of children with a diagnosis of ASD with significant language delays and another sub-group who do not have early language delays. The impact of these early language delays on the trajectory of language development is not yet properly understood, particularly whether these children do in fact recover and ‘catch up’ on language functions. Therefore, ongoing research is needed to further understand the language trajectories of children with ASD with and without early language delays. This body of work addressed whether the impact these early language delays manifest in language function later in development. In so doing, it also addresses whether the manifestation of early delays on later language function differentiates between individuals with HFA and AD. Further, this body of work also addressed whether any delays or deficits found in language function were specific to the language domain, or is a consequence of a more general cognitive delay or dysfunction. On-line paradigms from the domains of psycholinguistics and cognitive psychology were utilized to directly examine the lexical, conceptual and general information processing capacities of individuals with HFA and AD, the first study to introduce psycholinguistics to the ASD population. Chapter 3 examined the automatic lexical processing system. The results indicated that individuals with AD exhibited an intact and automatic lexical processing system that relied on finely-tuned orthographic processes in word recognition. However, findings regarding the lexical processing system in individuals with HFA were ambiguous; there was less reliance on orthographic representation to recognize written words, which suggests the lexical processing system is either delayed or structurally different in HFA. Chapter 4 investigated the nature of the lexical processing impairments specific to HFA observed in Chapter 3 by examining the organization and specificity of the lexical processing system. This experiment confirmed that while the lexical processing system was appropriately developed (specific) in individuals with AD, lexical processes were less developed (less specific) in individuals with HFA, with the lexical processes either not yet developed or atypically tuned in some autistic individuals. Taken together, the findings from Chapters 3 and 4 indicated the differences in one of the fundamental language functions, the lexical processing system, existed between individuals with HFA and AD and was evident later in development. Chapter 5 investigated whether distinctions between HFA and AD also extend to the conceptual memory system. The findings indicated that the conceptual memory processes for both disorders was consistent with conceptual memory processes observed in typically developing populations, and there were no differences between individuals with HFA and AD. Chapter 6 employed a novel visual information processing task, the Subtle Cognitive Impairment Test (SCIT), to examine the speed and effectiveness (efficiency) of information processes in HFA and AD. The findings indicated there were no differences between the HFA and AD groups concerning the efficiency of general information processing. However, a sub-group of individuals with ASD, unrelated to the autism/ Asperger’s disorder distinction, exhibited significant processing impairments, whilst another sub-group demonstrated information processing efficiency that was indistinguishable from that observed in typically developing individuals. A summary of overall findings across lexical, conceptual and general information processing systems revealed HFA and AD can be differentiated by fundamental differences in the lexical processing system, with no diagnostic differences regarding the conceptual processing system or information processing efficiency. Thus, language delays do distinguish HFA from AD, even later in development. Moreover, this is consistent with current diagnostic criteria differentiating HFA and AD on the basis of early language delays. These findings may have important outcomes on developing specific and comprehensive treatments for individuals with ASD.