3. Results
Subjects’ judgments mark two zones in the red–green continua: a zone where a green hue is perceived and a zone where a red hue is perceived. Overlapping red and green zones mark the forbidden region wherein red and green hues coexist perceptually. Disjoint red and green zones correspond to yellow colors wherein red and green hues are mutually exclusive.
Figure 4(a) and 4(b) shows the results of two subjects who are typical of the majority of our subjects. The diamonds at the end of the red and green bars represent boundaries determined in tasks GR1–GR4 (bars labeled 1 to 4). The top two panels refer to neon stimuli (Experiment 1), the bottom two to solid stimuli (Experiment 2). For both stimulus types, the red and green zones overlap for the RGC∗ stimulus set, representing colors seen as both red and green, but are disjoint in the RGC stimulus
set, consistent with yellow colors that are neither red nor green. Hysteresis (e.g., the difference between 1 and 4 in Fig. 4(a), top) is found for both RGC and RGC∗ in both neon and solid stimulus configurations.
The histograms in Fig. 5 show the extent of the overlap/gap between red and green zones measured in experiments with neon (panel a) and solid stimuli (panel b). A gap, predicted by opponent color theory, is shown as a negative overlap. The RGC∗ data reveal that perception of reddish-green colors is common for both neon and solid stimuli. Overlap is observed in about 70% of subjects. In contrast, a clear gap between red and green zones exists for almost all subjects in the RGC data sets for both neon and solid stimuli.
Using median values for GR1–GR4 yields essentially the same results with respect to an overlap between red and green perceptual zone. The overlap was observed for the RGC∗ stimulus set in about 77% of the subjects.