Attentional deficits have been reported in individuals with autism spectrum disorders (ASD), purportedly linked to an inability to adequately control the attention field (the location and spread of visual spatial attention). Over the past 30 years, the field of visual psychophysics has developed rigorous methods for measuring and characterizing attention. The primary aim of this research project is to apply the full force of the attention researcher’s methodological toolkit to the question of attention field control in ASD, interpreting the results within the context of a quantitative computational model of how attention modulates neural activity and behavior. This study will test the hypothesis that exogenous attention operates reflexively and automatically in individuals with ASD and that the attentional modulation of performance accuracy is comparable to that seen in typically developing individuals. Data in support of this hypothesis would rule out exogenous attention dysfunction in ASD and would validate the use of exogenous cues in subsequent experiments. Alternatively, uncovering deficits in exogenous attention in ASD would be an important contribution given the reflexive nature of the exogenous attentional system. Such a result would call for further research not only in the cortical and subcortical structures that are believed to support exogenous attentional function, but also in the kinds of developmental deficits that might be related to a malfunctioning exogenous attentional system. This research will also use spatial uncertainty to manipulate attention field size and characterize (first behaviorally and then with fMRI) any differences between ASD and matched control individuals in their ability to widen the attention field. Previous behavioral and neuroimaging research by this research team that focused on typically developing individuals demonstrated that attention fields are wider with spatial uncertainty than without it. This result was predicted by a computational theory of attention. The current study aims to replicate this finding in matched control participants, but failing to find wider attention fields for individuals with ASD would provide strong neurobiological support for a deficit in attention field size control in ASD. The study will also examine individual differences within the ASD group to further probe the relationship between brain function, behavioral performance, and severity of diagnosis.