Memory for the color of non‐monochromatic lights

Abstract

AbstractThe aim of this work was to explore the limits of memory for the hue of coloured illumination using nonspectral colours. Eighty‐four undergraduate optometry students with normal colour vision as assessed by the Ishihara 38 plate test, were given 10 s to memorize the hue of a luminous surface (luminance 120 cd m−2), subtending 22 by 18 degrees in an otherwise unlit room. The sample hue was one of 12 samples with chromaticity spaced evenly every 30 degrees around a hue circle in the CIE UCS diagram. The circle, radius 0.06, was centered at the chromaticity of D65 (u′ = 0.198, v′ = 0.468). The hue was displaced randomly by between 40 and 100 degrees, and the participants were required to use one of two keys to return the hue to its original appearance. The keys changed CIE 1976 hue angle (huv) by 1 degree, one in a clockwise and the other in a counterclockwise direction, but left the CIE 1976 saturation (suv) and the luminance unchanged. Each participant saw the to‐be‐memorized hue once only and made subsequent adjustments without seeing it again. Four adjustments were made immediately, four after 1 h, and a further four after 1 week. The second and the fourth in each set of four were preceded by a clockwise displacement of hue angle and the remaining two by an anticlockwise displacement. The CIE 1976 UCS chromaticity of the standard and the chromaticity of the very first adjustment performed immediately after the presentation of the standard were separated by 0.0210 (s.d. 0.0178) averaged across hues. One hue (purple) was more readily nameable than the others and was more accurately reproduced. There was no evidence of stable individual differences in observers' memory: observers' accuracy in reproducing one colour was not significantly correlated with their accuracy in reproducing another. Adjustments made after an interval of 1 h were worse than those undertaken immediately, but no better than those performed after 1 week. The variability of hue memory under these conditions was similar to the variability of coloured surfaces under common sources of illumination. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 11–15, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20281