Running Head: SEQUENCE EFFECTS IN autism

PSL*. We would like to thank Neil Stewart for supplying the 42 stimulus presentation orders and the children and staff who assisted with the study. Sequence Effects in Autism 2 Categorization decisions that reflect constantly changing memory representations may be an important adaptive response to dynamic environments. We assessed one such influence from memory, sequence effects, on categorization decisions made by individuals with autism. A model of categorization (i.e. Memory and Contrast model, Stewart, Brown, & Chater, 2002) assumes that contextual influences in the form of sequence effects drive categorization performance in individuals with typical development. Difficulties with contextual processing in autism, described by the weak central coherence account (Frith, 1989; Frith & Happé, 1994) imply reduced sequence effects for this participant group. The experiment reported here tested this implication. High functioning children and adolescents with autism (aged 10 to 15 years), matched on age and IQ with typically developing children, completed a test that measures sequence effects (i.e. category contrast effect task, Stewart et al., 2002) using auditory tones. Participants also completed a pitch discrimination task to measure any potential confound arising from possible enhanced discrimination sensitivity within the ASD group. The typically developing group alone demonstrated a category contrast effect. The data suggest that this finding cannot be attributed readily to participant group differences in discrimination sensitivity, perseveration, difficulties on the associated binary categorization task, or greater reliance upon long-term memory. We discuss the broad methodological implication that comparison between autism and control group responses to sequential perceptual stimuli may be confounded by the influence of preceding trials. We also discuss implications for the weak central coherence account and models of typical cognition. Sequence Effects in Autism 3 Autism spectrum disorders (ASDs) are neurodevelopmental conditions diagnosed on the basis of behaviors such as impairments in communication and reciprocal social interaction. Early researchers into autism suggested that difficulties with conceptual representation and categorization were also central to the condition 1945). Some researchers have suggested that such difficulties may underpin or exacerbate difficulties processing social information (Gastgeb, Strauss, & Minshew, 2006; Klinger & Dawson, 1995). For example, a father struggled to teach his son with autism to stay away from strangers (Klinger & Dawson, 1995). The son could not readily grasp the meaning of the concept and kept asking for a set of if then rules to define the category. Despite these theoretical and anecdotal suggestions of a categorization impairment, …