title: Foveal spatial summation in human cone mechanism.
abstract: We measured at the fovea the chromatic contrast threshold for stimuli modulated along different chromatic directions in the isoluminant plane of MBDKL colour space, considering the two cardinal axes (L/M) and S/(L + M) and other intermediate non-cardinal directions. This psychophysical determination was conducted as a function of stimulus size. The test stimulus was a foveal isoluminant Gaussian patch with a raised cosinusoidal temporal profile superimposed on a neutral background. The task was performed binocularly. The increment threshold was measured for three observers by a Bayesian adaptive psychometric method (QUEST). The Ricco area of complete spatial summation was estimated from the threshold-versus-area curves. The perceptive fields are smaller for the L/M-cone opponent direction than the S/(L + M)-cone opponent. The perceptive field sizes for the stimuli in non-cardinal chromatic directions and stimuli modulated at the (L/M)-cone opponent direction present similar values. Measurements were made at two luminance levels, 5 and 40 cd m(-2), but the differences found were small. The perceptive field sizes found could be associated with LGN area.
authors.affiliation: Departamento de Luminotecnia Luz y Visión "Ing. Herberto C. Bühler", Facultad de Ciencias Exactas y Tecnologia, Universidad Nacional de Tucumán, Av. Independencia 1800, San Miguel de Tucumán, Argentina. bodonell@herrera.unt.edu.ar
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: O'Donell
authors.forename: Elisa M
authors.initials: EM
authors.lastname: Colombo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001499:Bayes Theorem; D003118:Color Perception / Q000502:physiology*; D005260:Female; D005584:Fovea Centralis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics / Q000379:methods; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology