Figure 2.

(a) Temporal tuning functions: relative sensitivity (minimum 75% threshold amplitude divided by 75% threshold amplitude) as a function of temporal frequency for each of four observers. All of the functions are of lowpass character, with relative sensitivity falling to 1/2 of maximum sensitivity at 3–6 Hz. These data perfectly match previous measured temporal tuning functions of the third-order system. (b) Results of isoluminant pedestal tests for the same four observers: pedestaled vs. motion stimuli alone. Although observers could make reliable, correct motion–direction judgments in the absence of pedestal (69–94% correct depending on the actual amplitude of the chromatic modulation), adding a 2× pedestal reduced to chance the observers’ ability to perceive consistent motion from isoluminant displays.