The relative numbers of long-wavelength-sensitive to middle-wavelength-sensitive cones in the human fovea centralis

Abstract

Abstrset-The determination of the relative numbers of different cone types in the human retina is fundamental to our understanding of visual sensitivity and color vision; yet direct measurements which provide this basic information have not previously been made for ail cone types. Here we present a model which links the detection of a test light of small dimension to the number of cones contributing to detecfon of the light. We selectively isolated either the long-wavelength-sensitive (L) or the middle-wavelengthsensitive (M) cones, by choosing combinations of wavelengths of adapting backgrounds and tests to favor detection by the cone class of interest. Our model was applied to the detection functions measured for six color normal observers to obtain estimates of the relative numbers of L to M cones. Our estimates ranged between 1.46 and 2.36 for our observers with a mean value near two L cones for every M cone in human fovea centralis. ConesHuman fovea centralis Relative numbers of L to M cones ~RODU~ONThe determination of the relative numbers of different cone types in the retina is fundamental to our understanding of human visual sensitivity and color vision, and this information would be required for any quantitative models of human vision. Direct measurements which provide this basic information have not been previously made for all cone types. There continues to be a gratifying convergence of psychophysically derived evidence from humans ~Williams et al., 1981) and anatomically derived evidence from baboon (Marc and Sperling, 1977), macaque (deMonasterio et al., 1985), and human (Ahnelt et al., 1987) on the numerosity and distribution of the shortwavelength-sensitive (S) cones in the primate retina.In the cases of the long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones, there are no previous direct psychophysical measurements from which the relative numbers of L and M cones can be derived, and estimates based on various indirect means vary widely. To our knowledge, DeVries (1946DeVries ( , 1948 was the first to suggest that the individual variability in luminosity functions could be related to individual variability in the relative numbers of different cone types. Rushton and Baker (1964) subsequently reported that retinal densitometric measurements yielding the density of M and L cone pigments could be correlated to the flicker photometric matches between red and green lights made by their observers. Rushton and Baker's estimates, based on densitometric measurements, of the relative numbers of L to M cones in normal trichromatic observers spanned a wide range of three times more L as compared to M cones to one third as many L as compared to h4 cones. Another approach has been based on estimates deriving from curve fits required to make various sets of psychophysical data consistent one to another. Examples of this kind of analysis include Walraven's (1974) and Smith and Pokorny's (1975) estimates based on fits of the cone primaries to the luminosity function; Vos and Walraven's (1971)...

The density of cones in the fovea centralis of the human dichromat

“…Determinations of the best-fitting theoretical functions (Cicerone & Nerger, 1989 and as described below) for our measurements were made by a least-squares method ("zxssqz" subroutine from the IMSL Mathematical Library).…”

“…The results for these dichromats were compared to those of six color normal trichromatic observers whose results have been presented in detail elsewhere (Cicerone & Nerger, 1985 The remaining two dichromats (LH and KG) and two trichromat (VV and HA) were mildly myopic and optical corrections were applied for these observers.…”

“…The control of the experiment was aided by a computer (Apple HE). The apparatus has previously been described in detail (Cicerone & Nerger, 1989).…”

Organization of the Human Trichromatic Cone Mosaic

“…Similarly, fine isoluminant chromatic patterns can appear as luminance and chromatic spatial noise (Sekiguchi et al, 1993). Another example is that subjects routinely misjudge the color appearance of tiny flashes of monochromatic light (Holmgren, 1884;Hartridge, 1954;Krauskopf, 1964Krauskopf, , 1978Cicerone and Nerger, 1989;Hofer et al, 2005).…”

“…Whereas the short-wavelength-sensitive-(S) cone submosaic has been relatively well characterized (Williams et al, 1981;de Monasterio et al, 1985;Ahnelt et al, 1987;Curcio et al, 1991), the organization of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in the human retina has proven more elusive, because they exhibit no known morphological or histochemical differences and their pigments are 96% identical (Nathans et al, 1986). Several studies using indirect measurements have suggested that there are on average more L cones than M cones, with large intersubject variability (DeVries, 1946;Rushton and Baker, 1964;Cicerone and Nerger, 1989;Pokorny et al, 1991;Yamaguchi et al, 1997;Hagstrom et al, 1998;Brainard et al, 1999;Deeb et al, 2000;Kremers et al, 2000;Otake and Cicerone, 2000;Carroll et al, 2002). A limitation of these estimates is that they often involve the untested assumption that each M cone and each L cone contribute equally to the molecular, physiological, or psychophysical mechanisms being monitored to derive L:M ratio estimates.…”