The effect of flicker on foveal and peripheral thresholds for oscillatory motion

This study evaluated the influence of superimposed luminance flicker on the detection of oscillatory motion. Thresholds for oscillatory motion were determined in the fovea and at 2, 6 and 25 deg in the right field for a small luminous target with and without sinusoidal luminance flicker. At the fovea, flicker modulation up to 80% at frequencies from 1.5 to 9 Hz had no effect on motion detection, except for oscillatory motion at a frequency of 8 Hz, for which thresholds were elevated by about 0.2 log units. In the periphery, flicker elevated motion thresholds up to 0.3-0.4 log units at low and moderate frequencies of oscillation at all locations tested. However, both foveal and peripheral motion thresholds were unaffected by flicker when the luminance of the target was reduced. The absence of a robust effect of target flicker on motion thresholds may be accounted for in part by the comparison of activity across a large population of motion-detecting neurons with different direction preferences. Another contributing factor may be the existence of foveal velocity- and position-detecting mechanisms with similar sensitivities.