Jessica M. Smith¹, Bradford Z. Mahon; ¹Carnegie Mellon University

Category-specific responses in the ventral stream have traditionally been understood as due to processing of visual inputs through the geniculostriate pathway. Recent findings, however, suggest that visual inputs processed by nongeniculostriate pathways modulate patterns of category-specific neural responses in the ventral stream (Garcea et al., 2018; Vuilleumier et al. 2004; Bar et al., 2006). To isolate nongeniculostriate contributions to category-specific processing in the ventral stream, we studied cortically blind participants (n=3) with phenomenological blindness in part of their visual field due to a geniculostriate lesion. Despite that disruption to ‘seeing’, intact nongeniculostriate pathways can still process visual information in the cortically blind field, a phenomenon called blindsight. While previous research with this population has demonstrated neural responses to unseen stimuli in cortical and subcortical regions, it is unknown if the ventral stream receives input from nongeniculostriate pathways in the absence of seeing. We present here fMRI and connectivity analyses to investigate a) the presence of ventral stream responses to objects presented in the blind field and b) the patterns of structural and functional connectivity that underlie those effects. Each participant completed a task in which neutral faces, fearful faces, tools, or gabor patches were presented to the seen or blind field. Functional ROIs were defined with an independent category localizer in which stimuli were presented at central fixation. We found continued category-specific responses in the ventral stream for ‘unseen’ stimuli, including right lateral fusiform gyrus activity for unseen faces, and bilateral inferior temporal gyrus activity for unseen tools. Nongeniculostriate pathways generate fast orienting responses to salient stimuli, which may shape detailed perceptual analysis supported through the geniculostriate pathway. These results demonstrate that nongeniculostriate pathways contribute to category-specific neural responses in the ventral stream, challenging models of ventral stream organization that focus entirely on inputs contributed through the geniculostriate pathway.