Figure 5.

Speed discrimination in pursuit and perception in three subjects. A, Threshold time course for discrimination of small differences in target speed expressed as a fraction of base speed (15°/s). For pursuit traces (black), time is relative to pursuit onset; for perception (red), time represents viewing duration. Error bars in pursuit (gray regions) and perception (not visible) indicate SDs. B, Fractional speed discrimination thresholds (base speed, 10°/s) for noisy-dots speed targets plotted as a function of log2 of the SD of dot speeds, a measure of noise level. Perceptual thresholds (red circles) were measured at a 240 ms viewing duration; pursuit thresholds (black squares) at 240 ms after pursuit onset.