Moving vernier in amblyopic and peripheral vision: greater tolerance to motion blur

The purpose of this study was to examine the hypothesis that higher stimulus velocities could be tolerated in amblyopic and normal peripheral vision. The basis for this hypothesis is that a shift in the spatial scale of processing appears to account for the degradation in vernier acuity for moving stimuli in normal vision, and, to a large degree for the degradation in vernier acuity for stationary stimuli in amblyopic and peripheral vision. Vernier thresholds were determined using a pair of long abutting lines, for velocities ranging between 0 and 8 deg/sec. Comparisons were made between non-amblyopic and amblyopic eyes in two amblyopic observers, and between central and peripheral (5 and 10 deg) vision in two normal observers. We analyzed our threshold vs velocity data using an equivalent noise analysis, and defined the knee of the function, the point at which vernier threshold is elevated by a factor of square root of 2, as the "critical velocity" beyond which image motion degrades vernier acuity. Critical velocities were found to be higher in amblyopic than in nonamblyopic eyes; and higher in peripheral than central vision. Our results are consistent with the predictions from the shift in spatial scale notion--that higher velocity of image motion can be tolerated because of the shift in sensitivity toward lower spatial-frequency filter mechanisms in amblyopic and normal peripheral vision.