Abstract
Purpose: Crowding is known to be a limiting factor for spatial vision both in normal periphery, and in the central visual field of amblyopes. However, the spatio-temporal dynamics of crowding have received little attention. The current study investigates the spatio-temporal perceptive field for crowding for both normal and amblyopic observers. Method: We measured orientation discrimination of the target (Gabor patch) embedded in similar flankers randomly presented at a combination of positions (five possible separations) and times (nine frames with 30ms for each frame), at the fovea and 5 degrees in the lower visual field of two normal and three amblyopic observers. Correlations between the flanker spatio-temporal positions and the observers' performance were calculated to obtain spatio-temporal classification images for crowding. Results: For normal central vision, the spatio-temporal map of crowding is almost flat with a small elevation only at time zero and the smallest separation. In normal periphery, the space-time inseparable crowding map shows a much higher peak. Along the time axis, at the smallest separation, the curve is fit by a Gaussian with mean 0ms and a width (two standard deviations) of 60ms; along the space axis, at time zero, the curve is fit by a half Gaussian with mean 0ms and a width of 1.5 deg in the periphery. For amblyopic observers, the crowding map obtained from the central visual field has a shape similar to that of normal periphery, the width of which along space axis depends upon the amblyopic observer's crowded acuity but the width along the time axis may be broader in general. Conclusion: Our study provides new results revealing the dynamics of crowding in space and time. Crowding in amblyopic central vision has various spatial extents but a broader time course than normal peripheral vision.