Abstract

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

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References

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  1. G. Verriest, “Further studies on acquired deficiency of color discrimination,” J. Opt. Soc. Am. 53, 185–195 (1963).
    [CrossRef] [PubMed]
  2. V. C. Smith, J. Pokorny, A. S. Pass, “Color-axis determination on the Farnsworth–Munsell 100-hue test,” Am. J. Ophthalmol. 100, 176–182 (1985).
    [PubMed]
  3. K. Knoblauch, F. Saunders, M. Kusuda, R. Hynes, M. Podgor, K. E. Higgens, M. deMosasterio, “Age and illuminance effects in the Farnsworth–Munsell 100-hue test,” Appl. Opt. 26, 1441–1448 (1987).
    [CrossRef] [PubMed]
  4. A. Pinckers, “Color vision and age,” Ophthalmologica 181, 23–30 (1980).
    [CrossRef] [PubMed]
  5. K. J. Bowman, M. J. Collins, C. J. Henry, “The effect of age on performance on the panel D-15 and the desaturated D-15: a quantitative evaluation,” in Colour Vision Deficiencies, G. Verriest, ed. (Junk, The Hague, The Netherlands, 1984).
  6. K. H. Ruddock, “The effect of age upon colour vision. I. Response in the receptoral system of the human eye,” Vision Res. 5, 37–45 (1965).
    [CrossRef] [PubMed]
  7. K. Shinomori, J. S. Werner, “Individual variation in wavelength discrimination: task and model analysis,” in Proceedings of the 8th Congress of the International Colour Association (Color Science Association of Japan, Tokyo, 1997), Vol. I, pp. 195–198.
  8. J. S. Werner, “Development of scotopic sensitivity and the absorption spectrum of the human ocular media,” J. Opt. Soc. Am. 72, 247–258 (1982).
    [CrossRef] [PubMed]
  9. R. A. Weale, “Age and the transmittance of the human crystalline lens,” J. Physiol. (London) 395, 577–638 (1988).
  10. B. E. Schefrin, K. Shinomori, J. S. Werner, “Contributions of neural pathways to age-related losses in chromatic discrimination,” J. Opt. Soc. Am. A 12, 1233–1241 (1995).
    [CrossRef]
  11. D. M. Purdy, “On the saturations and chromatic thresholds of the spectral colours,” Br. J. Psychol. 21, 283–313 (1931).
  12. L. C. Martin, F. L. Warburton, W. J. Morgan, “The determination of the sensitiveness of the eye to differences in the saturation of colours,” G. B. Med. Res. Counc. 188, 5–42 (1933).
  13. W. D. Wright, F. H. G. Pitt, “The saturation-discrimination of two trichromats,” Proc. Phys. Soc. London 49, 329–331 (1937).
    [CrossRef]
  14. J. H. Nelson, “The colour-vision characteristics of a trichromat, part 2,” Proc. Phys. Soc. London 49, 332–337 (1937).
    [CrossRef]
  15. I. G. Priest, F. G. Brickwedde, “Minimum perceptible colorimetric purity as a function of dominant wavelength,” J. Opt. Soc. Am. 28, 133–139 (1938).
    [CrossRef]
  16. D. L. MacAdam, “Visual sensitivities to color differences in daylight,” J. Opt. Soc. Am. 32, 247–274 (1942).
    [CrossRef]
  17. G. Wyszecki, G. H. Fielder, “New color-matching ellipses,” J. Opt. Soc. Am. 61, 1135–1152 (1971).
    [CrossRef] [PubMed]
  18. P. K. Kaiser, J. P. Comerford, D. M. Bodinger, “Saturation of spectral lights,” J. Opt. Soc. Am. 66, 818–826 (1976).
    [CrossRef]
  19. E. Kimura, “Effects of luminance level on the saturation function—sensitivities based on saturation discrimination,” Color Res. Appl. 16, 289–296 (1991).
    [CrossRef]
  20. J. M. Kraft, J. S. Werner, “Aging and the saturation of colors. 2. Scaling of color appearance,” J. Opt. Soc. Am. A 16, 231–235 (1999).
    [CrossRef]
  21. J. S. Werner, B. E. Schefrin, “Loci of achromatic points throughout the life span,” J. Opt. Soc. Am. A 10, 1509–1516 (1993).
    [CrossRef] [PubMed]
  22. J. M. Kraft, J. S. Werner, “Spectral efficiency across the life span: flicker photometry and brightness matching,” J. Opt. Soc. Am. A 11, 1213–1221 (1994).
    [CrossRef]
  23. P. K. Kaiser, “Sensation luminance: a new name to distinguish CIE luminance from luminance dependent on an individual’s spectral sensitivity,” Vision Res. 28, 455–456 (1988).
    [CrossRef]
  24. I. Powell, “Lenses for correcting chromatic aberration of the eye,” Appl. Opt. 20, 4152–4155 (1981).
    [CrossRef] [PubMed]
  25. G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
    [CrossRef] [PubMed]
  26. L. O. J. Harvey, “Efficient estimation of sensory thresholds,” Behav. Res. Methods Instrum. 18, 623–632 (1986).
    [CrossRef]
  27. J. J. Vos, “Colorimetric and photometric properties of a 2° fundamental observer,” Color Res. Appl. 3, 125–128 (1978).
    [CrossRef]
  28. W. R. J. Brown, D. L. MacAdam, “Visual sensitivities to combined chromaticity and luminance differences,” J. Opt. Soc. Am. 39, 808–834 (1949).
    [CrossRef] [PubMed]
  29. W. R. J. Brown, “The influence of luminance level on visual sensitivity to color differences,” J. Opt. Soc. Am. 41, 684–688 (1951).
    [CrossRef] [PubMed]
  30. V. Smith, J. Pokorny, “Spectral sensitivity of the foveal cone photopigments between 400 and 500 nm,” Vision Res. 15, 161–171 (1975).
    [CrossRef] [PubMed]
  31. The effect of age-related changes in the ocular media depends primarily on the short-wavelength quantal spectrum of the broadband light, emitted by a 1-kW xenon lamp in the current experiment. The tristimulus values (XYZ) of the broadband light were known, but its quantal spectrum after passing through the optical system was not, so a model of xenon lamp spectra was used to estimate the spectrum of the light from its tristimulus coordinates. In the model three basis functions were determined by a principal-components analysis of five measured xenon spectra obtained from a 300-W xenon lamp whose beam passed through optics comparable with those used in the current experiment and that differ primarily because of passing through different neutral-density filters. The measured and the modeled spectra have almost exactly the same shape between 400 and 450 nm, suggesting that the effects of differential ocular media density on this light can be estimated well.
  32. M. L. Bieber, J. M. Kraft, J. S. Werner, “Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions,” Vision Res. 38, 1961–1966 (1998).
    [CrossRef] [PubMed]
  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.
  35. T. Yeh, V. C. Smith, J. Pokorny, “Colorimetric purity discrimination: data and theory,” Vision Res. 33, 1847–1857 (1993).
    [CrossRef] [PubMed]
  36. R. A. Weale, The Aging Eye (Lewis, London, 1963).
  37. Although we did not individually equate the luminance of the broadband standard in our experiment, the relatively small contribution of short-wavelength light to its total luminance minimizes the change in its sensation luminance (0.2 log unit) over the age range tested.
  38. B. E. Schefrin, J. S. Werner, M. Plach, N. Utlaut, E. Switkes, “Sites of age-related sensitivity loss in a short-wave cone pathway,” J. Opt. Soc. Am. A 9, 355–363 (1992).
    [CrossRef] [PubMed]
  39. J. S. Werner, V. G. Steele, “Sensitivity of human foveal color mechanisms throughout the life span,” J. Opt. Soc. Am. A 5, 2122–2130 (1988).
    [CrossRef] [PubMed]
  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).

1999

1998

M. L. Bieber, J. M. Kraft, J. S. Werner, “Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions,” Vision Res. 38, 1961–1966 (1998).
[CrossRef] [PubMed]

1995

1994

1993

J. S. Werner, B. E. Schefrin, “Loci of achromatic points throughout the life span,” J. Opt. Soc. Am. A 10, 1509–1516 (1993).
[CrossRef] [PubMed]

T. Yeh, V. C. Smith, J. Pokorny, “Colorimetric purity discrimination: data and theory,” Vision Res. 33, 1847–1857 (1993).
[CrossRef] [PubMed]

1992

1991

E. Kimura, “Effects of luminance level on the saturation function—sensitivities based on saturation discrimination,” Color Res. Appl. 16, 289–296 (1991).
[CrossRef]

1988

R. A. Weale, “Age and the transmittance of the human crystalline lens,” J. Physiol. (London) 395, 577–638 (1988).

J. S. Werner, V. G. Steele, “Sensitivity of human foveal color mechanisms throughout the life span,” J. Opt. Soc. Am. A 5, 2122–2130 (1988).
[CrossRef] [PubMed]

P. K. Kaiser, “Sensation luminance: a new name to distinguish CIE luminance from luminance dependent on an individual’s spectral sensitivity,” Vision Res. 28, 455–456 (1988).
[CrossRef]

1987

1986

L. O. J. Harvey, “Efficient estimation of sensory thresholds,” Behav. Res. Methods Instrum. 18, 623–632 (1986).
[CrossRef]

1985

V. C. Smith, J. Pokorny, A. S. Pass, “Color-axis determination on the Farnsworth–Munsell 100-hue test,” Am. J. Ophthalmol. 100, 176–182 (1985).
[PubMed]

1982

1981

1980

A. Pinckers, “Color vision and age,” Ophthalmologica 181, 23–30 (1980).
[CrossRef] [PubMed]

1978

J. J. Vos, “Colorimetric and photometric properties of a 2° fundamental observer,” Color Res. Appl. 3, 125–128 (1978).
[CrossRef]

1976

1975

V. Smith, J. Pokorny, “Spectral sensitivity of the foveal cone photopigments between 400 and 500 nm,” Vision Res. 15, 161–171 (1975).
[CrossRef] [PubMed]

1971

1966

G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
[CrossRef] [PubMed]

1965

K. H. Ruddock, “The effect of age upon colour vision. I. Response in the receptoral system of the human eye,” Vision Res. 5, 37–45 (1965).
[CrossRef] [PubMed]

1963

1951

1949

1942

1938

1937

W. D. Wright, F. H. G. Pitt, “The saturation-discrimination of two trichromats,” Proc. Phys. Soc. London 49, 329–331 (1937).
[CrossRef]

J. H. Nelson, “The colour-vision characteristics of a trichromat, part 2,” Proc. Phys. Soc. London 49, 332–337 (1937).
[CrossRef]

1933

L. C. Martin, F. L. Warburton, W. J. Morgan, “The determination of the sensitiveness of the eye to differences in the saturation of colours,” G. B. Med. Res. Counc. 188, 5–42 (1933).

1931

D. M. Purdy, “On the saturations and chromatic thresholds of the spectral colours,” Br. J. Psychol. 21, 283–313 (1931).

Bieber, M. L.

M. L. Bieber, J. M. Kraft, J. S. Werner, “Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions,” Vision Res. 38, 1961–1966 (1998).
[CrossRef] [PubMed]

Bodinger, D. M.

Bowman, K. J.

K. J. Bowman, M. J. Collins, C. J. Henry, “The effect of age on performance on the panel D-15 and the desaturated D-15: a quantitative evaluation,” in Colour Vision Deficiencies, G. Verriest, ed. (Junk, The Hague, The Netherlands, 1984).

Brickwedde, F. G.

Brown, W. R. J.

Collins, M. J.

K. J. Bowman, M. J. Collins, C. J. Henry, “The effect of age on performance on the panel D-15 and the desaturated D-15: a quantitative evaluation,” in Colour Vision Deficiencies, G. Verriest, ed. (Junk, The Hague, The Netherlands, 1984).

Comerford, J. P.

deMosasterio, M.

Fielder, G. H.

Harvey, L. O. J.

L. O. J. Harvey, “Efficient estimation of sensory thresholds,” Behav. Res. Methods Instrum. 18, 623–632 (1986).
[CrossRef]

Henry, C. J.

K. J. Bowman, M. J. Collins, C. J. Henry, “The effect of age on performance on the panel D-15 and the desaturated D-15: a quantitative evaluation,” in Colour Vision Deficiencies, G. Verriest, ed. (Junk, The Hague, The Netherlands, 1984).

Higgens, K. E.

Hynes, R.

Kaiser, P. K.

P. K. Kaiser, “Sensation luminance: a new name to distinguish CIE luminance from luminance dependent on an individual’s spectral sensitivity,” Vision Res. 28, 455–456 (1988).
[CrossRef]

P. K. Kaiser, J. P. Comerford, D. M. Bodinger, “Saturation of spectral lights,” J. Opt. Soc. Am. 66, 818–826 (1976).
[CrossRef]

Kimura, E.

E. Kimura, “Effects of luminance level on the saturation function—sensitivities based on saturation discrimination,” Color Res. Appl. 16, 289–296 (1991).
[CrossRef]

Knoblauch, K.

Kraft, J. M.

Kusuda, M.

MacAdam, D. L.

Martin, L. C.

L. C. Martin, F. L. Warburton, W. J. Morgan, “The determination of the sensitiveness of the eye to differences in the saturation of colours,” G. B. Med. Res. Counc. 188, 5–42 (1933).

Morgan, W. J.

L. C. Martin, F. L. Warburton, W. J. Morgan, “The determination of the sensitiveness of the eye to differences in the saturation of colours,” G. B. Med. Res. Counc. 188, 5–42 (1933).

Nelson, J. H.

J. H. Nelson, “The colour-vision characteristics of a trichromat, part 2,” Proc. Phys. Soc. London 49, 332–337 (1937).
[CrossRef]

Pass, A. S.

V. C. Smith, J. Pokorny, A. S. Pass, “Color-axis determination on the Farnsworth–Munsell 100-hue test,” Am. J. Ophthalmol. 100, 176–182 (1985).
[PubMed]

Pinckers, A.

A. Pinckers, “Color vision and age,” Ophthalmologica 181, 23–30 (1980).
[CrossRef] [PubMed]

Pitt, F. H. G.

W. D. Wright, F. H. G. Pitt, “The saturation-discrimination of two trichromats,” Proc. Phys. Soc. London 49, 329–331 (1937).
[CrossRef]

Plach, M.

Podgor, M.

Pokorny, J.

T. Yeh, V. C. Smith, J. Pokorny, “Colorimetric purity discrimination: data and theory,” Vision Res. 33, 1847–1857 (1993).
[CrossRef] [PubMed]

V. C. Smith, J. Pokorny, A. S. Pass, “Color-axis determination on the Farnsworth–Munsell 100-hue test,” Am. J. Ophthalmol. 100, 176–182 (1985).
[PubMed]

V. Smith, J. Pokorny, “Spectral sensitivity of the foveal cone photopigments between 400 and 500 nm,” Vision Res. 15, 161–171 (1975).
[CrossRef] [PubMed]

Powell, I.

Priest, I. G.

Purdy, D. M.

D. M. Purdy, “On the saturations and chromatic thresholds of the spectral colours,” Br. J. Psychol. 21, 283–313 (1931).

Ruddock, K. H.

K. H. Ruddock, “The effect of age upon colour vision. I. Response in the receptoral system of the human eye,” Vision Res. 5, 37–45 (1965).
[CrossRef] [PubMed]

Saunders, F.

Schefrin, B. E.

Shinomori, K.

B. E. Schefrin, K. Shinomori, J. S. Werner, “Contributions of neural pathways to age-related losses in chromatic discrimination,” J. Opt. Soc. Am. A 12, 1233–1241 (1995).
[CrossRef]

K. Shinomori, J. S. Werner, “Individual variation in wavelength discrimination: task and model analysis,” in Proceedings of the 8th Congress of the International Colour Association (Color Science Association of Japan, Tokyo, 1997), Vol. I, pp. 195–198.

Smith, V.

V. Smith, J. Pokorny, “Spectral sensitivity of the foveal cone photopigments between 400 and 500 nm,” Vision Res. 15, 161–171 (1975).
[CrossRef] [PubMed]

Smith, V. C.

T. Yeh, V. C. Smith, J. Pokorny, “Colorimetric purity discrimination: data and theory,” Vision Res. 33, 1847–1857 (1993).
[CrossRef] [PubMed]

V. C. Smith, J. Pokorny, A. S. Pass, “Color-axis determination on the Farnsworth–Munsell 100-hue test,” Am. J. Ophthalmol. 100, 176–182 (1985).
[PubMed]

Steele, V. G.

Switkes, E.

Utlaut, N.

Verriest, G.

Vos, J. J.

J. J. Vos, “Colorimetric and photometric properties of a 2° fundamental observer,” Color Res. Appl. 3, 125–128 (1978).
[CrossRef]

Warburton, F. L.

L. C. Martin, F. L. Warburton, W. J. Morgan, “The determination of the sensitiveness of the eye to differences in the saturation of colours,” G. B. Med. Res. Counc. 188, 5–42 (1933).

Weale, R. A.

R. A. Weale, “Age and the transmittance of the human crystalline lens,” J. Physiol. (London) 395, 577–638 (1988).

R. A. Weale, The Aging Eye (Lewis, London, 1963).

Werner, J. S.

J. M. Kraft, J. S. Werner, “Aging and the saturation of colors. 2. Scaling of color appearance,” J. Opt. Soc. Am. A 16, 231–235 (1999).
[CrossRef]

M. L. Bieber, J. M. Kraft, J. S. Werner, “Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions,” Vision Res. 38, 1961–1966 (1998).
[CrossRef] [PubMed]

B. E. Schefrin, K. Shinomori, J. S. Werner, “Contributions of neural pathways to age-related losses in chromatic discrimination,” J. Opt. Soc. Am. A 12, 1233–1241 (1995).
[CrossRef]

J. M. Kraft, J. S. Werner, “Spectral efficiency across the life span: flicker photometry and brightness matching,” J. Opt. Soc. Am. A 11, 1213–1221 (1994).
[CrossRef]

J. S. Werner, B. E. Schefrin, “Loci of achromatic points throughout the life span,” J. Opt. Soc. Am. A 10, 1509–1516 (1993).
[CrossRef] [PubMed]

B. E. Schefrin, J. S. Werner, M. Plach, N. Utlaut, E. Switkes, “Sites of age-related sensitivity loss in a short-wave cone pathway,” J. Opt. Soc. Am. A 9, 355–363 (1992).
[CrossRef] [PubMed]

J. S. Werner, V. G. Steele, “Sensitivity of human foveal color mechanisms throughout the life span,” J. Opt. Soc. Am. A 5, 2122–2130 (1988).
[CrossRef] [PubMed]

J. S. Werner, “Development of scotopic sensitivity and the absorption spectrum of the human ocular media,” J. Opt. Soc. Am. 72, 247–258 (1982).
[CrossRef] [PubMed]

K. Shinomori, J. S. Werner, “Individual variation in wavelength discrimination: task and model analysis,” in Proceedings of the 8th Congress of the International Colour Association (Color Science Association of Japan, Tokyo, 1997), Vol. I, pp. 195–198.

Westheimer, G.

G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
[CrossRef] [PubMed]

Wright, W. D.

W. D. Wright, F. H. G. Pitt, “The saturation-discrimination of two trichromats,” Proc. Phys. Soc. London 49, 329–331 (1937).
[CrossRef]

Wyszecki, G.

Yeh, T.

T. Yeh, V. C. Smith, J. Pokorny, “Colorimetric purity discrimination: data and theory,” Vision Res. 33, 1847–1857 (1993).
[CrossRef] [PubMed]

Am. J. Ophthalmol.

V. C. Smith, J. Pokorny, A. S. Pass, “Color-axis determination on the Farnsworth–Munsell 100-hue test,” Am. J. Ophthalmol. 100, 176–182 (1985).
[PubMed]

Appl. Opt.

Behav. Res. Methods Instrum.

L. O. J. Harvey, “Efficient estimation of sensory thresholds,” Behav. Res. Methods Instrum. 18, 623–632 (1986).
[CrossRef]

Br. J. Psychol.

D. M. Purdy, “On the saturations and chromatic thresholds of the spectral colours,” Br. J. Psychol. 21, 283–313 (1931).

Color Res. Appl.

J. J. Vos, “Colorimetric and photometric properties of a 2° fundamental observer,” Color Res. Appl. 3, 125–128 (1978).
[CrossRef]

E. Kimura, “Effects of luminance level on the saturation function—sensitivities based on saturation discrimination,” Color Res. Appl. 16, 289–296 (1991).
[CrossRef]

G. B. Med. Res. Counc.

L. C. Martin, F. L. Warburton, W. J. Morgan, “The determination of the sensitiveness of the eye to differences in the saturation of colours,” G. B. Med. Res. Counc. 188, 5–42 (1933).

J. Opt. Soc. Am.

J. Opt. Soc. Am. A

J. Physiol. (London)

R. A. Weale, “Age and the transmittance of the human crystalline lens,” J. Physiol. (London) 395, 577–638 (1988).

Ophthalmologica

A. Pinckers, “Color vision and age,” Ophthalmologica 181, 23–30 (1980).
[CrossRef] [PubMed]

Proc. Phys. Soc. London

W. D. Wright, F. H. G. Pitt, “The saturation-discrimination of two trichromats,” Proc. Phys. Soc. London 49, 329–331 (1937).
[CrossRef]

J. H. Nelson, “The colour-vision characteristics of a trichromat, part 2,” Proc. Phys. Soc. London 49, 332–337 (1937).
[CrossRef]

Vision Res.

K. H. Ruddock, “The effect of age upon colour vision. I. Response in the receptoral system of the human eye,” Vision Res. 5, 37–45 (1965).
[CrossRef] [PubMed]

P. K. Kaiser, “Sensation luminance: a new name to distinguish CIE luminance from luminance dependent on an individual’s spectral sensitivity,” Vision Res. 28, 455–456 (1988).
[CrossRef]

G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
[CrossRef] [PubMed]

V. Smith, J. Pokorny, “Spectral sensitivity of the foveal cone photopigments between 400 and 500 nm,” Vision Res. 15, 161–171 (1975).
[CrossRef] [PubMed]

M. L. Bieber, J. M. Kraft, J. S. Werner, “Effects of known variations in photopigments on L/M cone ratios estimated from luminous efficiency functions,” Vision Res. 38, 1961–1966 (1998).
[CrossRef] [PubMed]

T. Yeh, V. C. Smith, J. Pokorny, “Colorimetric purity discrimination: data and theory,” Vision Res. 33, 1847–1857 (1993).
[CrossRef] [PubMed]

Other

R. A. Weale, The Aging Eye (Lewis, London, 1963).

Although we did not individually equate the luminance of the broadband standard in our experiment, the relatively small contribution of short-wavelength light to its total luminance minimizes the change in its sensation luminance (0.2 log unit) over the age range tested.

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.

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.

The effect of age-related changes in the ocular media depends primarily on the short-wavelength quantal spectrum of the broadband light, emitted by a 1-kW xenon lamp in the current experiment. The tristimulus values (XYZ) of the broadband light were known, but its quantal spectrum after passing through the optical system was not, so a model of xenon lamp spectra was used to estimate the spectrum of the light from its tristimulus coordinates. In the model three basis functions were determined by a principal-components analysis of five measured xenon spectra obtained from a 300-W xenon lamp whose beam passed through optics comparable with those used in the current experiment and that differ primarily because of passing through different neutral-density filters. The measured and the modeled spectra have almost exactly the same shape between 400 and 450 nm, suggesting that the effects of differential ocular media density on this light can be estimated well.

K. Shinomori, J. S. Werner, “Individual variation in wavelength discrimination: task and model analysis,” in Proceedings of the 8th Congress of the International Colour Association (Color Science Association of Japan, Tokyo, 1997), Vol. I, pp. 195–198.

K. J. Bowman, M. J. Collins, C. J. Henry, “The effect of age on performance on the panel D-15 and the desaturated D-15: a quantitative evaluation,” in Colour Vision Deficiencies, G. Verriest, ed. (Junk, The Hague, The Netherlands, 1984).

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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Figures (5)

Fig. 1
Fig. 1

Log Pc discrimination sensitivity (250 td) for two observers plotted as a function of wavelength for two separate sessions (points). Model fits (solid curves) are derived from pooled data from both sessions. Arrows at 500 nm indicate the location of a local reduction in slope, as described in the text.

Fig. 2
Fig. 2

Log relative Pc discrimination sensitivity (250 td) plotted as a function of wavelength for three younger and three older observers. The initials and the age (in years) of the observer are listed above each function. Each set of data is arbitrarily displaced along the ordinate. Solid curves show model fits. Circles, squares, and triangles denote the best, average, and worst model fits from each age group.

Fig. 3
Fig. 3

Mean log Pc discrimination sensitivity at two retinal illuminance levels plotted as a function of wavelength. Circles show data for younger observers; triangles show data for older observers. Error bars denote the standard error of the mean where it is larger than the point. Solid curves represent model fits.

Fig. 4
Fig. 4

Log sensitivity of S-cone and L/M-cone chromatic mechanisms (based on model fits) at two light levels plotted as a function of age. The least-squares regression line is shown for each set of data. Slopes are presented in Table 2.

Fig. 5
Fig. 5

Log ratio of estimated S-cone mechanism sensitivity to L/M-cone mechanism sensitivity plotted as a function of age. The least-squares linear regression function for data in each plot is shown. The difference in mean level between the functions in each plot (boldface arrow) represents the degree to which the S-cone mechanism is more sensitive than the L/M-cone mechanism at 250 td compared with 10 td (tritan shift).

Tables (2)

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Table 1 Pc Discrimination Data [log(1/Pc)] for Older and Younger Groups Corrected on the Basis of the Luminosity Function of Vos’s Standard Observer

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Table 2 Slopes (Log Units per Decade) of Regression Lines Relating Mechanism Sensitivity to Age

Equations (8)

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Q(LBB)=λ=400700(BBλLλ/10LENSλLENSobs+MPλMPobs)/FBB,
Q(Lλ)=Lλ/Fobs,
Q(Mλ)=Mλ/Fobs,
Q(Sλ)=Sλ/Fobs,
Fobs=(robsLλ+Mλ)(2L570+M570)/[robs(L570+M570)],
ΔLMλ=[Q(LBB)-Q(Lλ)-Q(MBB)+Q(Mλ)]LMobs,
ΔSλ=[Q(SBB)-Q(Sλ)]Sobs,
SSE=λ=420680{log(1/THRλ)-log[(ΔLMλ2+ΔSλ2)0.5]}2,

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