Topographic mapping of visual sensations in a completely blind individual

Non-optic sight (NOS) is a phenomenon in which blind individuals have visual sensations of things they touch, hear, or otherwise sense in their surroundings. The current study is exploring the neural correlates of NOS in a woman (subject NS) who lost her sight to retinal degeneration. The images that NS sees are primarily triggered through touch and proprioception (e.g., if she picks up a mug, she sees a mug). Unlike imagery, these images are determinate, involuntary, and persist as long as she infers the object remains in her line-of-sight. In a previous fMRI experiment, NS placed simple 3D shapes in her field-of-view. The resulting BOLD signals hinted at visual cortical topographic mapping of the "seen" objects (smaller shapes evoked more foveal activation). To test whether this activity really follows "retinotopic" organization, we designed and 3D-printed tactile versions of retinotopic mapping stimuli (3-dimensional wedge and bar) which could be used within a 7T scanner. Every 8s, NS was cued to either rotate the wedge around a fixed point (16 positions) or shift the bar up/down or left/right (9 positions each). We then performed population receptive field mapping using the brain data and the stimuli translated into 2D apertures. Receptive field parameters across NS’s visual cortex showed a striking topographic organization resembling typical sighted retinotopy: increasing eccentricity moving anteriorly from the occipital pole and voxels tuned to portions of the visual field that are contralateral and flipped relative to their respective cortical locations. Fascinatingly, some phase reversals can even be observed occurring roughly at the anatomical locations where transitions between V1/2/3 are typically seen. These results represent the first topographic mapping of stimuli experienced as visual perceptions in a completely blind individual and demonstrates that the visual cortex can support concrete visual experiences that accurately interpret non-retinal sensory input, even in blindness.