title: Influence of background size, luminance and eccentricity on different adaptation mechanisms.
abstract: Mechanisms of light adaptation have been traditionally explained with reference to psychophysical experimentation. However, the neural substrata involved in those mechanisms remain to be elucidated. Our study analyzed links between psychophysical measurements and retinal physiological evidence with consideration for the phenomena of rod-cone interactions, photon noise, and spatial summation. Threshold test luminances were obtained with steady background fields at mesopic and photopic light levels (i.e., 0.06-110cd/m(2)) for retinal eccentricities from 0° to 15° using three combinations of background/test field sizes (i.e., 10°/2°, 10°/0.45°, and 1°/0.45°). A two-channel Maxwellian view optical system was employed to eliminate pupil effects on the measured thresholds. A model based on visual mechanisms that were described in the literature was optimized to fit the measured luminance thresholds in all experimental conditions. Our results can be described by a combination of visual mechanisms. We determined how spatial summation changed with eccentricity and how subtractive adaptation changed with eccentricity and background field size. According to our model, photon noise plays a significant role to explain contrast detection thresholds measured with the 1/0.45° background/test size combination at mesopic luminances and at off-axis eccentricities. In these conditions, our data reflect the presence of rod-cone interaction for eccentricities between 6° and 9° and luminances between 0.6 and 5cd/m(2). In spite of the increasing noise effects with eccentricity, results also show that the visual system tends to maintain a constant signal-to-noise ratio in the off-axis detection task over the whole mesopic range.
authors.affiliation: Departamento de Óptica, Universidad de Valladolid, P. Belén 7, 47011 Valladolid, Spain.
authors.forename: Alejandro H
authors.initials: AH
authors.lastname: Gloriani
authors.affiliation: Departamento de Óptica, Universidad de Valladolid, P. Belén 7, 47011 Valladolid, Spain.
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: Matesanz
authors.affiliation: Departamento de Luminotecnia, Luz y Visión, Universidad Nacional de Tucumán, Instituto de Investigación en Luz, Ambiente y Visión, CONICET-UNT, Avenida de Independencia 1800, 4000 Tucumán, Argentina.
authors.forename: Pablo A
authors.initials: PA
authors.lastname: Barrionuevo
authors.affiliation: Departamento de Óptica, Universidad de Valladolid, P. Belén 7, 47011 Valladolid, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Arranz
authors.affiliation: Departamento de Luminotecnia, Luz y Visión, Universidad Nacional de Tucumán, Instituto de Investigación en Luz, Ambiente y Visión, CONICET-UNT, Avenida de Independencia 1800, 4000 Tucumán, Argentina.
authors.forename: Luis
authors.initials: L
authors.lastname: Issolio
authors.affiliation: Departamento de Óptica, Universidad de Valladolid, P. Belén 7, 47011 Valladolid, Spain.
authors.forename: Santiago
authors.initials: S
authors.lastname: Mar
authors.affiliation: Departamento de Óptica, Universidad de Valladolid, P. Belén 7, 47011 Valladolid, Spain. Electronic address: juanantonio.aparicio@uva.es.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Aparicio
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D006801:Humans; D008029:Lighting; D055255:Mesopic Vision; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology*; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D059629:Signal-To-Noise Ratio; D014794:Visual Fields / Q000502:physiology
keywords: Light adaptation; Photon noise; Psychophysics; Retinal gain control; Rod-cone interaction