title: Estimating the gradient direction of a luminance ramp.
abstract: We report on the extent to which human observers are able to indicate the gradient direction of a luminance ramp. In our experiment modulation depth ranged from 1 to 64% and field sizes subtended 0.5 to 47.5 degrees of visual angle. Observers are not able to indicate the gradient direction for modulation depths below 6%. For values above this threshold, the angular standard deviation in the responses decreases proportionally with the logarithm of the modulation depth and is about 11 degrees for a modulation depth of 64%. The angular standard deviations for supra-threshold contrast are slightly increased for the field sizes of 0.5 and 47.5 degrees but are constant over a range of field sizes of 1 to 25 degrees. Thus, size invariance holds well for this range of field sizes.
authors.affiliation: Utrecht Biophysics Research Institute (UBI), University of Utrecht, The Netherlands.
authors.forename: R G
authors.initials: RG
authors.lastname: Erens
authors.forename: A M
authors.initials: AM
authors.lastname: Kappers
authors.forename: J J
authors.initials: JJ
authors.lastname: Koenderink
mesh_terms: D015350:Contrast Sensitivity / Q000502:physiology; D006801:Humans; D008027:Light; D008297:Male; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology; D013028:Space Perception / Q000502:physiology*