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, perseverance, 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. Teaching programmes represent an important means of assisting individuals with the developmental condition, autism. Such individuals tend to have distinctive patterns of learning and thought processes. A greater understanding of how these patterns differ from those of the general population will assist the development of such programmes. This project aims to increase this understanding by examining the influence of context on categorization abilities. Participants will encounter a series of auditory tones and will be asked to categorise each tone according to pitch; high versus low. If individuals with autism are susceptible to category contrast effects, context, in the form of the preceding tone, will influence categorisation accuracy. For example, categorisation of a borderline high tone will be more accurate if the context is a very low tone (ie a distant member of the contrast category), than if the context is a very high tone (ie a distant member of the same category). A comparison of contrast effects shown by two groups of individuals, those with autism diagnoses and those without, will test competing predictions derived from several theoretical accounts. In this way, the work will contribute towards a greater understanding of learning processes in autism.

Methodologies comprised psychometric testing, and computer-run quantitative experiments. Opportunity and stratified sampling procedures were used. The populations comprised a group of 9 - 15 year old children with autism spectrum disorders, matched on age and IQ with a group of typically developing children.