title: L/M cone ratios in human trichromats assessed by psychophysics, electroretinography, and retinal densitometry.
abstract: Estimates of the relative numbers of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones vary considerably among normal trichromats and depend significantly on the nature of the experimental method employed. Here we estimate L/M cone ratios in a population of normal observers, using three psychophysical tasks-detection thresholds for cone-isolating stimuli at different temporal frequencies, heterochromatic flicker photometry, and cone contrast ratios at minimal flicker perception--as well as flicker electroretinography and retinal densitometry. The psychophysical tasks involving high temporal frequencies, specifically designed to tap into the luminance channel, provide average L/M cone ratios that significantly differ from unity with large interindividual variation. In contrast, the psychophysical tasks involving low temporal frequencies, chosen to tap into the red-green chromatic channel, provide L/M cone ratios that are always close to unity. L/M cone ratios determined from electroretinographic recordings or from retinal densitometry correlate with those determined from the high-temporal-frequency tasks. These findings suggest that the sensitivity of the luminance channel is directly related to the relative densities of the L and the M cones and that the red-green chromatic channel introduces a gain adjustment to compensate for differences in L and M cone signal strength.
authors.affiliation: Department of Experimental Ophthalmology, University of Tübingen Eye Hospital, Germany. jan.kremers@uni-tuebingen.de
authors.forename: J
authors.initials: J
authors.lastname: Kremers
authors.forename: H P
authors.initials: HP
authors.lastname: Scholl
authors.forename: H
authors.initials: H
authors.lastname: Knau
authors.forename: T T
authors.initials: TT
authors.lastname: Berendschot
authors.forename: T
authors.initials: T
authors.lastname: Usui
authors.forename: L T
authors.initials: LT
authors.lastname: Sharpe
mesh_terms: D003118:Color Perception / Q000502:physiology*; D003720:Densitometry; D004596:Electroretinography; D005260:Female; D006801:Humans; D008297:Male; D010783:Photometry; D011601:Psychophysics / Q000379:methods*; D012160:Retina / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012684:Sensory Thresholds