Einstina Wang¹ (), Dongcheng He², Susana T. L Chung¹; ¹University of California, Berkeley, ²Hefei Comprehensive National Science Center

The physiological blind spot, a photoreceptor-free retinal region, does not result in a lack of perception, due to the brain's filling-in process. Prior research highlights mostly V1-related features in filling-in. This study aimed to examine whether motion speed information can also "fill-in". After mapping out the blind spot of their right eye, seven participants with normal vision (age: 19-23 years) performed a speed judgment task monocularly, while fixating at a fixation target with eye movements monitored. Testing alternated between the two eyes. The stimulus comprised a vertical bar (width=1°) right of fixation, centered at the center of the blind spot. Two vertical patches (1°×6°) containing a horizontally-oriented grating were presented above and below the bar such that when viewed with the right eye, the two patches abutted the top and bottom edges of the blind spot, respectively. On any given trial (duration=1s), the spatial frequency (0.5, 1 or 1.5 cpd) and the motion direction (upward or downward) of the two grating-patches were identical; with one patch (randomly chosen) moving at 0.67 deg/s and the other moving at one of four speeds: 0.78, 0.97, 1.15 or 1.34 deg/s. Participants indicated which patch (top/bottom) moved faster. The point-of-subjective-equality (PSE) was determined from the psychometric function relating the proportion of upward responses with the speed difference between the two grating-patches. Our null hypothesis was that if motion speed did not induce filling-in within the blind spot, then the PSE for the right and left eyes should be the same. Across participants, we found a small effect of spatial frequency (p=0.044). Specifically, the PSE for the right and left eyes differed at 1 cpd, but not at the other two spatial frequencies. Our findings imply the possibility of a motion speed-induced filling-in of information within the blind spot, but the effect is apparently small.

Acknowledgements: UC Berkeley Rose Hills Summer Scholarship