title: Orientation tuning in human colour vision at detection threshold.
abstract: We measure the orientation tuning of red-green colour and luminance vision at low (0.375 c/deg) and mid (1.5 c/deg) spatial frequencies using the low-contrast psychophysical method of subthreshold summation. Orientation bandwidths of the underlying neural detectors are found using a model involving Minkowski summation of the rectified outputs of a bank of oriented filters. At 1.5 c/deg, we find orientation-tuned detectors with similar bandwidths for chromatic and achromatic contrast. At 0.375 c/deg, orientation tuning is preserved with no change in bandwidth for achromatic stimuli, however, for chromatic stimuli orientation tuning becomes extremely broad, compatible with detection by non-oriented colour detectors. A non-oriented colour detector, previously reported in single cells in primate V1 but not psychophysically in humans, can transmit crucial information about the color of larger areas or surfaces whereas orientation-tuned detectors are required to detect the colour or luminance edges that delineate an object's shape.
authors.affiliation: McGill Vision Research, Department of Ophthalmology H4.14, 687 Pine Ave West, Montreal, Quebec, H3A 1A1 Canada.
authors.forename: Mina
authors.initials: M
authors.lastname: Gheiratmand
authors.affiliation: McGill Vision Research, Department of Ophthalmology H4.14, 687 Pine Ave West, Montreal, Quebec, H3A 1A1 Canada.
authors.forename: Kathy T
authors.initials: KT
authors.lastname: Mullen
mesh_terms: D000465:Algorithms; D055253:Color Vision; D015350:Contrast Sensitivity; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D010775:Photic Stimulation; D012684:Sensory Thresholds