Purity discrimination: successive vs simultaneous comparison method.

Purity discrimination thresholds (delta p) were measured with successive (SOA = 3 sec) and simultaneous (SOA = 0 sec) comparison methods for seven dominant wavelengths; 410, 480, 500, 530, 570, 600 and 650 nm. The stimulus duration was 1 sec. The delta p values with the successive comparison method were found to be about 1.5-2.0 times larger than those obtained in the simultaneous case. The degree of purity discrimination deterioration shown in this study is similar to that of wavelength discrimination deterioration previously reported (Uchikawa and Ikeda, 1981, Vision Res. 21, 591-595). Saturation shifts of stimuli with the successive comparison method were also observed; these were toward increased saturation direction for most dominant wavelengths.