Effects of luminance and isoluminant masking noise on second-order chromatic smooth motion

Purpose: It has been reported that second-order chromatic apparent motion is influenced by first-order isoluminant chromatic noise but not by first-order luminance noise. The aim of this study is to investigate whether these effects emerge for apparent motion alone or whether these effects are generally observed for second-order chromatic smooth motion. Methods: We measured simple detection and direction discrimination thresholds for luminance and chromatic drifting gratings in the presence of luminance or isoluminant chromatic noise. A 0.25 cycle/deg envelope motion was produced by contrast modulation of a 1 cycle/deg carrier component composed by anti-phase modulation of red and green sinusoidal gratings. The contrast of 1D-spatial luminance or isoluminant noise, superimposed on the stimuli, was varied. The speed of the envelope motion was 1 deg/sec. All stimuli were presented on RGB monitor at 150 Hz. Results: 1. Detection and direction discrimination thresholds for isoluminant stimuli were not affected by the luminance noise, whereas both detection and direction discrimination thresholds for luminance stimuli increased as contrast of the luminance noise was increased. 2. The isoluminant chromatic noise influences motion discrimination of the isoluminant stimuli but not the luminance stimuli. Conclusions: There is a strong influence of isoluminant masking on second-order chromatic smooth motion identification but less or little effect of luminance masking. This is consistent with the previous study for second-order chromatic apparent motion. These results indicate that second-order chromatic motion is mediated by a genuine chromatic mechanism.