Effects of Light Wavelengths on the Performance of Color Absolute Judgments

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Optically, humans can discriminate between colors as close as 2nm in wavelength in relative judgment task. However, there is little research to discuss color differences for absolute color judgments in which the comparison is held in memory. Therefore, the intent of this study was to explore effects of wavelengths on the Just Noticeable Difference (JND) of absolute judgments in our perceptual world. A color identification task was utilized to investigate the JND of wavelengths. In the experiment, the Standard Stimulus Color (SSC) and the Comparison Stimulus Color (CSC) were successively presented. The SSC which was presented first must be stored in working memory and recalled when the second color, CSC, is presented. Subjects had to decide if the CSC matched the SSC. Each CSC was presented four times for each subject in the experiment. The CSC wavelength that was recognized as different from the SSC twice was designed as a JND wavelength. Five SSC wavelengths with 100% saturation and 100% lightness were chosen from the hue circle of HLS color space which included 360 hues. Because the hue circle is a circle, the CSC may be on both sides of a SSC in the hue circle. The CSC hue which may be located on the clockwise direction or counter clockwise direction of the SSC was called clockwise direction color (CD) or counter clockwise direction color (CCD), respectively. The wavelengths expressed with HLS color space were translated into coordination of CIE1931 (x, y)-chromaticity diagram. The results indicated that threshold sensitivities varied for different wavelengths on absolute judgment tasks. The lights with longest or shortest wavelength had greater JNDs than ones with middle wavelengths for absolute judgment tasks. The comparison of the results of the experiment on absolute color judgment tasks and MacAdam’s (1942) findings for relative color judgment tasks were also discussed.