title: Detection and discrimination of subjective contours defined by offset gratings.
abstract: Three experiments were conducted to refine our understanding of the mechanisms that encode subjective contours. In Experiment 1, discrimination thresholds (stimulus onset asynchronies [SOAs] yielding 81% correct) were measured in a backward masking paradigm for subjective contours defined by offset gratings. For large apertures, thresholds increased as carrier frequency increased. For the smallest aperture, thresholds were a U-shaped function of carrier frequency. Experiment 2 showed that these threshold results were generally consistent with the rated strength of the subjective contours. Experiment 3 showed that detection thresholds (SOAs yielding 81% correct) again increased with carrier spatial frequency, increased for obliquely oriented carriers, and, for a particular frequency and orientation of the carrier, were lower when the subjective contour was orthogonal to the carrier. All of these results are well explained by a two-stage process in which a second-layer filter integrates the responses of end-stopped mechanisms to the terminators defining the subjective contour. In the model, the end-stopped mechanisms have low-pass sensitivity to carrier spatial frequency, and the sizes of the second-layer filters are proportional to the scale of the end-stopped mechanisms from which they draw their input.
authors.affiliation: Department of Psychology, Concordia University, Montréal, Québec, Canada. gurnsey@vax2.concordia.ca
authors.forename: R
authors.initials: R
authors.lastname: Gurnsey
authors.forename: M
authors.initials: M
authors.lastname: Iordanova
authors.forename: D
authors.initials: D
authors.lastname: Grinberg
mesh_terms: D004056:Differential Threshold; D005403:Fixation, Ocular / Q000502:physiology; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D012680:Sensitivity and Specificity