Measurement of Central and Peripheral Dynamic Visual Acuity Thresholds during Ocular Pursuit of a Moving Target

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Abstract
Previously, visual acuity thresholds for eccentric retinal points have been documented for targets that oscillate while the observer fixates a central point. This research describes the situation where the observer tracks a moving target in constant linear motion, thereby involving the pursuit and saccadic eye movements. The increase of visual acuity thresholds with target motion (0 to 70°/s) was evaluated as a function of retinal eccentricity. Nine retinal points were evaluated, (central, 5° and 10° nasal, 5° and 10° temporal, 5° and 10° superior, and 5° and 10° inferior to the fovea). Eight normal subjects viewed computer-generated randomly oriented E's monocularly through a horizontally rotating mirror. A computer automatically calculated the minimal angle of resolution (MAR) threshold values. Result indicated that the change in visual acuity thresholds was dependent upon retinal location. The thresholds for central and peripheral eccentricities plotted as a function of angular velocity were linear but the slope of the linear function was much reduced for peripherally viewed targets compared to centrally viewed targets. Although both peripheral and central visual acuity thresholds may increase with increasing target velocity due to velocity mismatch errors and saccadic suppression and/or omission, the reduction in slope for peripherally viewed targets may be due to differential temporal summation, retinal smear, and/or separate retinogeniculate pathway processing.

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