The findings indicate that visual acuity assessment in Chinese readers is complicated by the spatial complexity of Chinese characters, but the fact that the Snellen E, which is the current national standard of acuity measurement in China, and Chinese characters showed similar dependence on optical defocus may indicate a potentially valid way to infer functional vision in Chinese readers with Snellen E acuity.

Written Chinese is distinct from alphabetic languages because of its enormous number of characters with a great range of spatial complexities (stroke numbers). In this study we investigated the impact of spatial complexity on legibility of Chinese characters as well as associated crowding in peripheral vision. Our results showed that for isolated characters, threshold sizes of complex characters increased faster with retinal eccentricity than did those of simple characters, suggesting possible "within-character" crowding among parts of complex Chinese characters. However, such "within-character" crowding was rendered negligible by strong "between-character" crowding introduced by flankers. When the target and flankers belonged to different complexity groups, the intensity and extent of crowding were greatly reduced, which could be explained by top-down influences as well as lower-level mechanisms. We suggest that crowding can be attributed to multiple mechanisms at different levels of visual processing.

No abstract

Patients with a central scotoma usually use a preferred retinal locus (PRL) consistently in daily activities. The selection process and time course of the PRL development are not well understood. We used a gaze-contingent display to simulate an isotropic central scotoma in normal subjects while they were practicing a difficult visual search task. As compared to foveal search, initial exposure to the simulated scotoma resulted in prolonged search reaction time, many more fixations and unorganized eye movements during search. By the end of a 1782-trial training with the simulated scotoma, the search performance improved to within 25% of normal foveal search. Accompanying the performance improvement, there were also fewer fixations, fewer repeated fixations in the same area of the search stimulus and a clear tendency of using one area near the border of the scotoma to identify the search target. The results were discussed in relation to natural development of PRL in central scotoma patients and potential visual training protocols to facilitate PRL development.