Abstract:

PURPOSE: The human fovea serves both as the locus for ?xations and the ocul?omotor reference for saccades. Training normally sighted adults with occluded central vision can reliably induce a preferred retinal locus (PRL) in peripheral vision for ?xation with re-referenced saccades. Does the development of a PRL in peripheral vision alter the neural processing of the visual inputs? Crowding, the impediment of object recognition by clutter, is a hallmark of form-vision de?cits in peripheral vision. Here we asked if the spatial extent of crowding can be altered as a consequence of the training-induced PRL.
METHODS: We trained nine human subjects using the object-following-and-visual-search task with a simulated central-?eld scotoma and a prescribed PRL. Before and after training, we measured the spatial extent of crowding at two locations: the prescribed PRL location in the upper-left visual ?eld and a symmetric “sideways” location in the upper-right ?eld.
RESULTS: After training, subjects’ saccades were re-referenced to the prescribed PRL location in the presence of the simulated central scotoma. Training led to a shrinkage of the crowding zone along the radial axis at the PRL location, causing the crowding zone to become roundish. The crowding zone along the radial axis at the sideways location was also reduced. With fMRI measurements before and after training, we found a radial-specific reduction of crowding-related suppression across visual areas V1-V4, which was only observed at the PRL location.
CONCLUSIONS: These ?ndings suggest that human crowding zones dynamically reorganize relative to the reference point of saccade, which is consistent with the saccade-confounded image-encoding theory (Nandy & Tjan, 2012). By demonstrating that training with a simulated central-field scotoma facilitates peripheral vision via reshaping the crowding zones, this study reveals the residual plasticity in adult peripheral vision and sheds light on new mechanisms of rehabilitations for patients with central ?eld loss.