The influence of stimulus luminance and contrast on hyperacuity thresholds for oscillatory movement

Hyperacuity thresholds for oscillatory movement were determined under conditions of decreased contrast and decreased luminance. Responses were found to be resistant to contrast reduction down to 15%; below this level thresholds increased. The contrast response function is thus similar to that of the magnocellular channel of the visual system. Systematic reduction in luminance caused a corresponding rise in thresholds. It is suggested that this effect is due to undersampling of the retinal image as a result of a lowered quantal absorption and an increase in critical duration of temporal integration at lower levels of luminance.