Project Summary Autism is a pervasive developmental disorder that is characterized by impaired social cognition. Social cognition depends critically on basic perceptual processes, such as the visual perception of faces, mediated by the fusiform face area (FFA). In prior work, we have developed the ability to measure the structure of this region with unprecedented resolution, allowing us to partially elucidate the laminar structure of FFA. Our approach is focused on brain structure rather than function, which avoids potential confounds related to ability, attention, or motivation. We also focus on a small region, functionally defined in individual brains and retained in native space, which affords improved power to conduct hypothesis-driven research relative to methods that rely on atlas-based regions and group averaging. Our prior research suggests an inverse relation between FFA cortical thickness (CT) and perceptual performance, which is specific to face stimuli and does not extend to objects. When probed with ultra high-resolution (UHR) imaging, this effect is most consistent in the deepest layers of the FFA. Our preliminary data in autism guides the following hypotheses: 1) relative to adults without autism, autistic adults will show a higher FFA CT and a more generalized relation between FFA CT and performance of both faces and objects, and 2) the effect will be more distributed along the radial depth of the cortex than in non-autistic adults, reflecting different neuroplastic mechanisms. We will explore the implications of these differences beyond the visual system by measuring functionally-defined white matter passing through the FFA to the anterior temporal lobe. For this we will use a novel diffusion-weighted imaging pipeline that captures both microstructural and macrostructural features of fiber bundles to increase sensitivity to developmental and clinical changes. This project combines state-of-the-art imaging that affords ultra-high- resolution quantification of cortical gray and white matter structure with a comprehensive battery of perceptual tasks assessing face and object perception and memory. The outcome of this study will improve precision in measuring anomalous development of the FFA in autism, enabling localization to distinct cortical laminae and thus providing insight into the developmental timeline and neural mechanisms of altered experience-based perceptual learning of faces in autism.