title: The S-cone contribution to luminance depends on the M- and L-cone adaptation levels: silent surrounds?
abstract: Under dim background conditions, the S-cones make little or no contribution to luminance (A. Eisner & D. I. MacLeod, 1980; W. Verdon & A. J. Adams, 1987), yet under conditions of intense long-wavelength adaptation, a small but robust contribution to luminance--as defined by heterochromatic flicker photometry (A. Stockman, D. I. MacLeod, & D. D. DePriest, 1987, 1991) or motion (J. Lee & C. F. Stromeyer, 1989)--can be found. Here, by using selective adaptation and/or tritanopic metamers to isolate the S-cone response, we investigate the dependence of the S-cone luminance input on changes in background wavelength and radiance. Interestingly, the S-cone luminance input disappears completely when no adapting background is present, even though the same S-cone stimulus makes a clear contribution to luminance when a background is present. The dependence of the S-cone luminance input on the wavelength and radiance of the adapting background is surprising. We find that the S-cone signal can be measured on fields of 491 nm and longer wavelengths that exceed a criterion background radiance. These criterion radiances roughly follow an L + M spectral sensitivity, which suggests that the S-cone luminance input is silent unless the L- and M-cones are excited above a certain level. We hypothesize that the L + M cone signals produced by the steady adapting backgrounds somehow "gate" the S-cone luminance signals, perhaps by being modulated by them.
authors.affiliation: Institute of Ophthalmology, University College London, London, UK. c.ripamonti@ucl.ac.uk
authors.forename: Caterina
authors.initials: C
authors.lastname: Ripamonti
authors.forename: Wen Ling
authors.initials: WL
authors.lastname: Woo
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Crowther
authors.forename: Andrew
authors.initials: A
authors.lastname: Stockman
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D055253:Color Vision / Q000502:physiology*; D005260:Female; D005425:Flicker Fusion / Q000502:physiology; D006801:Humans; D057230:Limit of Detection; D008297:Male; D010775:Photic Stimulation; D010783:Photometry; D011601:Psychophysics; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology