The influence of luminance on displacement thresholds for continuous oscillatory movement

Displacement thresholds were determined for a sinusoidally-modulated contrast grating, having a spatial frequency of 2 c/deg, whose mean luminance could be varied. The grating underwent continuous oscillatory simple harmonic motion. Displacement thresholds were determined for frequencies of 1, 3, 5, 7 and 10 Hz using the method of limits for each mean grating luminance of 3.8, 8.9, 26, 62 and 134 cd/m2. With low oscillation frequencies a marked reduction in sensitivity is produced by reducing the mean luminance of the grating. This is not the case with higher oscillation frequencies when mean luminance has little effect upon sensitivity.