Abstract
Fixational eye movements introduce a temporal component to the encoding of spatial information. Psychophysical and computational work has shown that removing these temporal signals is detrimental to visual acuity for stimulus durations longer than 750 ms, suggesting the presence of mechanisms that leverage retinal motion over longer timescales to improve resolution. By contrast, early retinal neurons sum information over shorter intervals to minimize noise. Thus, when presentation durations are restricted, retinal motion may degrade the encoding of fine patterns, leading to impaired acuity. To characterize the impact of motion blur on visual acuity, we used an adaptive optics scanning laser ophthalmoscope with a 30-Hz frame rate to control the retinal trajectory of a tumbling-E stimulus delivered to the parafovea. For all measurements, stimulus duration was 3 frames (~66 ms). First, observers (n = 4) completed a tumbling-E task to determine the letter size that yielded 80% performance. Next, performance (% correct) for this fixed letter size (MAR range: 1.82-2.12 arcmin) was determined for three retinal motion conditions: natural retinal motion, retinally-stabilized, and imposed motion. For imposed motion, stimuli were moved on the retina in randomly-selected cardinal directions by increments of the optotype bar width; these motion increments included .5, 1 and 2 bar widths per frame. When the optotype’s retinal motion was parallel to its orientation, performance was invariant to motion magnitude and unchanged from the natural motion or retinally-stabilized conditions (p > .05, multiple comparison ANOVA). However, if the optotype’s retinal motion was orthogonal to its orientation, the maximal decrease in performance (relative to the equivalent parallel motion) occurred when the optotype moved by one bar width per frame (16% reduction). These results suggest the mechanisms responsible for high-acuity vision are susceptible to motion blur when retinal motion matches the spatial frequency of the stimulus being judged.