Objective: To estimate the prevalence of autism in an epidemiologically-derived population of adolescents with intellectual disabilities (ID). Method:The prevalence of autism was examined using the Autism Diagnostic Interview-Revised, with appropriate care taken in assessing lower functioning individuals and those with additional physical and sensory impairments. Individual assessment during psychological evaluation, and consensus classification of complex cases, involving clinicians experienced in the assessment of autism, contributed to the identification of autism.Results: Overall, 28% of individuals, or 2.0 of the 7.1/1000 with ID in the target population (as we have previously identified in another study), were identified with autism. Autism rates did not differ significantly across severe ID (32.0%) and mild ID (24.1%); males predominated (2.3 males to 1 female), but less so for severe ID (2 males to 1 female, compared with 2.8 males to 1 female for mild ID). Socioeconomic status did not distinguish the groups with and without autism. Less than one-half of the adolescents who met diagnostic criteria for autism were previously diagnosed as such. Conclusions:Our overall prevalence estimate for autism is in the higher range of estimates reported in previous studies of ID (more so for mild ID). This likely reflects the changes in diagnostic criteria for autism that have subsequently occurred. Discussion focuses on the identification of autism in the population with ID, and on the implications for service delivery and clinical training. Can J Psychiatry 2008;53(7):449-459Clinical Implications · Autism is a common coexisting condition in the population with ID. · The condition may remain unrecognized and (or) the symptoms of autism misattributed to other circumstances such as psychiatric disorder. · Services for individuals with ID need to recognize, and adequately support, those with coexisting autism. Limitations· An observational measure standardized specifically for the assessment of autism (for example, the Autism Diagnostic Observation Schedule) was not included. · Identifying the severity of the social-communicative impairment in individuals with ID, rather than identifying those who meet criteria for autism, is likely to have more practical relevance for identification of needs and service planning. · The relatively low prevalence rate for mild ID might have contributed to the higher prevalence rate for autism in this study, although our autism rates for mild, relative to severe, ID are consistent with those derived from recent general population surveys.

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This study examined the development of endogenous orienting in children ages 6, 10, and 14 years and in adults. Participants were asked to respond with a button press to targets appearing in the left or right visual field. Cues that correctly or incorrectly indicated the target's location preceded the appearance of targets at stimulus onset asynchronies (SOAs) of 100 and 800 msec. Cues that signaled a target's appearance, but not its location, were also included. In addition to raw reaction times, orienting effects, benefits, and costs were examined. Two main findings emerged: First, for all participants except the youngest children effect sizes increased with increasing SOA. The absence of an SOA effect in the youngest group is interpreted as evidence of their difficulty in voluntarily adjusting the scope of their attentional focus. In addition, field asymmetries changed with the age of the respondent: 6-year-olds showed a right-field advantage, 10-year-olds failed to show any laterality differences, and 14-year-olds and adults responded more quickly to targets in the left than in the right field. This finding is consistent with developmental data on a number of cognitive processes, and is interpreted within a developmental framework of right-hemisphere dominance for spatial orienting (cf. Mesulam, 1998).