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Andrew Stockman, Herbert Jägle, Markus Pirzer, Lindsay Sharpe; Vµ*(λ): a generalized luminous efficiency function for any condition of chromatic adaptation. Journal of Vision 2007;7(9):793. doi: 10.1167/7.9.793.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: We recently proposed a luminous efficiency function, V*(λ), for 2° photopic viewing based on heterochromatic flicker photometric (HFP) measurements made under daylight (D65) adaptation (Sharpe, Stockman, Jagla, & Jägle, 2005). V*(λ), is defined as a linear combination of the Stockman & Sharpe (2000) long-wavelength sensitive (L-) and middle-wavelength sensitive (M-) cone fundamentals. However, the applicability of V*(λ) is limited to its measuring conditions, because the relative contributions of the L- and M-cones to luminous efficiency depend strongly on the state of chromatic adaptation. Here, we extend its applicability by characterizing its dependence on background chromaticity.
Methods: 25 Hz HFP matches were obtained in 6 genotyped male observers on 23 different 3.0 log10 photopic troland adapting fields (µ): 14 spectral ones (µ = 430 to 670 nm); 7 bichromatic mixtures (µ = 478 + 577 nm) that varied in luminance ratio; and 2 corresponding to CIE Illuminants A and D65 daylight. Each of the resulting 23 luminous efficiency functions, Vµ*(λ), was characterized as a best-fitting linear combination of the cone fundamentals, aL(λ) + M(µ), where a, the L-cone weighting factor, varies with µ, the effective background wavelength.
Results: As expected, short-wavelength fields increase a, by decreasing the relative M-cone contribution, and long-wavelength fields decrease a, by decreasing the relative L-cone contribution. However, the changes in a are larger on short wavelengths fields and smaller on long-wavelengths ones than predicted from reciprocal sensitivity adjustment (Weber's Law). Shorter and longer wavelength chromatic fields both relatively suppress the M-cone contribution to Vµ*(λ) in excess of Weber's Law.
Conclusions: Our generalized model accounts for Weber's Law and the chromatic suppression of the M-cone contribution to Vµ*(λ). It allows a(µ), and therefore Vµ*(λ), to be predicted for a standard observer for any chromatic background of 1000 td.
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