EDGE-CURVATURE DISCRIMINABILITY ARGUES AGAINST EXPLICIT CURVATURE DETECTORS

Human discrimination of edge curvature was investigated over a 2-decad e range of curvatures. The luminance profile of the edge pattern was e ither sharp or blurred on a scale that varied over a range of almost 2 decades. The experiments with curved blurred stimuli can also be rega rded as investigations of contrast discrimination in which a blurred b ar is superimposed orthogonally upon a blurred edge. The discriminatio n thresholds for the blurred stimuli show substantial size invariance, which can be explained in terms of contrast discrimination and maskin g with orthogonally oriented patterns rather than in terms of curvatur e per se. No such size invariance is found with sharp stimuli. All res ults can be described by a simple model based only upon local contrast .