Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2014.Cataloged from PDF version of thesis.Includes bibliographical references (pages 124-143).The middle face patch is a region of cortex in the ventral visual pathway of the Inferior Temporal lobe in the macaque brain. This region has been identified by functional MRI to respond preferentially to images of faces over non-face images, similar to functionally defined face selective regions in the human brain. In this thesis we spatially map the category selective preference of 100's of multiunit sites in the cortical region localized to the fMRI face selective region with a novel X-ray imaging system. We observed evidence for an ~6mm region of cortex that was enriched with sites that demonstrate a category selective preference for images of faces. The number of face selective sites varied across the cortical region, and could peak as high as 96% near the center of the enriched zone to a baseline rate as low as 3% outside the face patch. Sites in the middle face patch displayed significant category selectivity for the conventional images of faces used in the experiment. Approximately 25% of the sites in the patch displayed high selectivity (d' > 2) for faces as compared to less than 1% of the sites sampled outside the patch. Given the limited image variability present in conventional image sets, we examined face detection performance in the middle face patch with a computationally non-trivial image set, that was nonetheless simple for human subjects. We found that under these conditions, sites in the middle face patch demonstrated a weak correlation to human face detection behavior. We conclude that the middle face patch is a region of cortex enriched with sites that participate in an intermediate level representation of faces.by Paul Aparicio.Ph. D.