Motion thresholds can be predicted from contrast discrimination

The detection thresholds for oscillatory motion and flicker were compared across a wide range of pedestal contrasts, spatial frequencies, and temporal frequencies in both foveal and peripheral vision. Motion and flicker stimuli were both generated by summation of a counterphase test grating with a static pedestal grating. For the oscillatory motion task the test and the pedestal were presented 90 deg out of phase to each other, whereas for flicker the two gratings were presented in phase. Since detection of both stimuli would depend on the same test stimulus, detection thresholds could be similar even though the tasks differ. Although there was a slight elevation in flicker detection thresholds compared with motion thresholds, our main finding is that oscillatory motion and flicker thresholds for suprathreshold sinusoidal gratings are similar. This finding supports the idea that motion and flicker have a common underlying detection mechanism. Our finding that flicker thresholds are slightly higher than jitter thresholds indicates that the contrast gain control (or saturating energy transducer) has a weak phase dependence. The ability to discriminate motion from flicker was elevated relative to their detection thresholds, particularly at high temporal frequencies. We offer two models to account for this behavior. The discrimination of motion from flicker may require a temporal comparison of the outputs of directionally selective filters tuned to opposite directions or to the population statistics of a bank of separable mechanisms.