title: Pulse and steady-pedestal contrast discrimination: effect of spatial parameters.
abstract: The goal of this study was to establish the spatial summation properties associated with inferred PC- and MC-pathway mediated psychophysical contrast discrimination. Previous work has established two paradigms that reveal characteristic signatures of these pathways. In the pulse paradigm, a four-square array was pulsed briefly, on a constant background. In the steady-pedestal paradigm, the stimulus array was presented continuously as a steady-pedestal within a constant surround. In both paradigms, one square differed from the others, giving the observer a forced choice spatial discrimination task. Area summation functions derived for the pulse paradigm decreased with area, with a slope of -0.25 on a log-log axis. Area summation functions derived for the steady-pedestal paradigm decreased as a power function of area, approaching an asymptote above one square degree. The latter are consistent with the classical data of threshold spatial summation.
authors.affiliation: Visual Sciences Center, The University of Chicago, 940 East 57th Street, 60637, Chicago, IL, USA. vc-smith@uchicago.edu
authors.forename: V C
authors.initials: VC
authors.lastname: Smith
authors.forename: V C
authors.initials: VC
authors.lastname: Sun
authors.forename: J
authors.initials: J
authors.lastname: Pokorny
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D011594:Psychometrics; D011601:Psychophysics; D014795:Visual Pathways / Q000502:physiology*