Differential motion thresholds to sinusoidal gratings at two eccentricities.

Differential motion thresholds were measured at eccentricities of 9 degrees and 16.6 degrees using computer-generated sinusoidal gratings. Three spatial frequencies (0.51, 0.25, and 0.13 cycles/deg) were examined at reference velocities of 2, 4, 8, 16, 32, and 48 deg/sec. Minimum differential velocity thresholds were between 20 and 30% of the reference velocities for the three spatial frequencies at both eccentricities. Increasing eccentricity produced an increase in the velocity at which minimum velocity discrimination occurred. Temporal frequency tuning was between 4 and 8 Hz, regardless of eccentricity.