Sensory abnormalities in individuals with autism

Sensory abnormalities are not a diagnostic criteria for autism but are often observed and described in first person accounts. Several hypotheses have been offered to explain these abnormalities. One model implicates the brainstem vestibular system. Other researchers have hypothesized that children with autism have a faulty arousal system and are either in a chronic state of overarousal or fluctuate between overarousal and underarousal. A recent theoretical model hypothesizes that sensory disturbances are due to an extended attention loop in which individuals with autism overfocus on features of objects. The ability to speculate about which theoretical model is best is limited by a lack of validated measures of sensory disturbances in autism. The Sensory Survey is based on the Sensory Profile by Dunn but was specifically modified for autism. It is a 103-item survey measuring overreactivity, underreactivity and sensory seeking behavior in each sensory domain plus movement. This survey was given to parents of 252 children with a diagnosis on the PDD spectrum in addition to a measure of overselective attention, a diagnostic checklist assessing severity of symptomotology, and a question assessing whether their children had an exceptional memory. Furthermore, 191 of the parents were administered the Vineland Adaptive Behavior Scales (VABS). Several theoretical predictions were tested. Over and under reactivity were positively correlated, lending support to the notion of fluctuating arousal. Sensory seeking was highly correlated with both over and under reactivity, indicating that seeking behaviors may serve different purposes for different individuals in different contexts. Stepwise regressions indicated that sensory abnormalities (especially underreactivity) were related to lower adaptive functioning even after the variance due to symptom severity and overfocusing was removed. A cluster analysis was performed, the results of which lend support to the overfocusing hypothesis. Approximately 10% of the sample had a strongly overfocused pattern of symptoms including overreactivity, perseverative behavior, overfocusing and having an exceptional memory. An additional 33% of the sample had a mildly overfocused pattern. Hypotheses about the origins of overfocusing behavior are discussed. The Sensory Survey has the potential to systematize our understanding of sensory disturbances for both research and clinical purposes.