Chromatic signal-to-noise ratio affects chromatic gamut effect

Introduction. If a chromatic contrast of a display were increased, a color patch of low chromatic saturation would appear nearly achromatic, and vice versa*. The current study will report a strong asymmetry in this chromatic gamut effect according to temporal modulation, which may provide a clue to clarify the mechanism of this phenomenon. Methods. An array of 44 × 33 multi-colored squares (36deg × 27deg) was presented as center- and surround-stimuli. The change in detection ratio for the center stimulus (probe; 2deg × 2deg) was measured during a slow change in chromatic contrast in the surround. The color of each square was randomly selected from 9 hues that equally distributed in hue around equal-energy white (W_eq). The chromaticity for the surround was varied in saturation, from zero to 0.050 in CIE u'v' distance from the W_eq, under isoluminance. A cycle of temporal modulation for the surround consisted of four 20s phases: 1) gray (W_eq , 2) increment, 3) maximum saturation and 4) decrement. In the phases 1 and 3, saturation was kept constant for 20s, at zero and 0.050, respectively. In the phases 2 and 4, saturation was modulated continuously between zero and 0.050 with an incremental- and a decremental-half of a raised-cosine envelope (0.025Hz), respectively. The chromatic modulation of the probe was independent from the surround, as a 1s raised-cosine envelope (1Hz) with the maximum saturation of 0.005 in u'v' distance. The probe was presented every 5s, except catch trials. 20 cycles were repeated in a session. Result. Results were analyzed according to signal detection theory. Hit rates were significantly different between the phases 2 and 4, as well as between the phases 1 and 3. The false-alarm rate was higher in the decrement phase than in the increment phase. Conclusion. The current result implies that the signal-to-noise ratio in the chromatic mechanism coulds be a cause of the gamut effect.