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Journal of the Optical Society of America A

Journal of the Optical Society of America A


  • Vol. 16, Iss. 2 — Feb. 1, 1999
  • pp: 223–230

Aging and the saturation of colors. 1. Colorimetric purity discrimination

James M. Kraft and John S. Werner  »View Author Affiliations

JOSA A, Vol. 16, Issue 2, pp. 223-230 (1999)

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Colorimetric purity (Pc) discrimination functions were measured for 21 color-normal observers (11 younger and 10 older observers with mean ages of 30 and 74 years, respectively). On each two-alternative-forced-choice trial, observers saw two flashes of light, a broadband white light [CIE(x, y)=(0.33, 0.35)] and a mixture of broadband and monochromatic light (420–680 nm). The observer’s task was to choose the flash that had a chromatic component. Foveally viewed, circular, 1.2°-diameter stimuli were presented as 1.5-s flashes with 3-s interstimulus intervals in Maxwellian view. Stimuli [250 trolands (td) and 10 td] were equated on the basis of individual heterochromatic flicker photometry functions. Measured Pc discrimination sensitivity was lower in the older group than in the younger group at both light levels, and the performance difference between the age groups was approximately constant across the spectrum. The difference between discrimination at 10 and 250 td was relatively small for the younger group but larger for the older group, indicating a selective performance decrement for older observers at low light levels. The data were modeled as a sum of differential responses from S-cone and L/M-cone chromatic channels. The model and the data indicate similar age-related losses of sensitivity in the two channels, perhaps secondary to receptoral sensitivity losses.

© 1999 Optical Society of America

OCIS Codes
(330.1720) Vision, color, and visual optics : Color vision
(330.4060) Vision, color, and visual optics : Vision modeling
(330.4300) Vision, color, and visual optics : Vision system - noninvasive assessment
(330.5510) Vision, color, and visual optics : Psychophysics
(330.6180) Vision, color, and visual optics : Spectral discrimination

Original Manuscript: June 5, 1998
Revised Manuscript: September 28, 1998
Manuscript Accepted: October 9, 1998
Published: February 1, 1999

James M. Kraft and John S. Werner, "Aging and the saturation of colors. 1. Colorimetric purity discrimination," J. Opt. Soc. Am. A 16, 223-230 (1999)

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  33. The model does seem to inappropriately smooth the shoulder (local reduction in slope near 500 nm), which is sometimes present in the data. See Figs. 1–3.
  34. The data point at 570 nm was omitted from the model fitting at 10 td to make the younger model fit comparable with the older model fit, for which no point at 570 nm was available. As Fig. 3 demonstrates, the fit to this point is good anyway. The mean parameter estimates for the L/M-cone and S-cone mechanisms change by only 0.01 and 0.03 log unit, respectively, when 570 nm is included in the fitting. The data point at 570 nm was included in all fits at 250 td. Note that all plotted mechanism sensitivities were shifted upward by 3 log units for convenience.
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  40. Some fraction of the observed age-related sensitivity loss could have been due to increases in ocular media density if the discriminations occurred at a point along the threshold-versus-radiance function where Weber’s law was violated. If this were the case, the slightly lower sensation luminance of the broadband standard for the older observers would cause them to require higher-purity stimuli for discrimination. If conservative assumptions are used, the proportions of the sensitivity loss attributable to increases in ocular media density are less than or equal to 0.03 (L/M mechanism, 250 td), 0.25 (S mechanism, 250 td), 0.36 (L/M mechanism, 10 td), and 0.38 (S mechanism, 10 td).

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Fig. 1 Fig. 2 Fig. 3
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