EDGE-CURVATURE DISCRIMINABILITY ARGUES AGAINST EXPLICIT CURVATURE DETECTORS

Human discrimination of edge curvature was investigated over a 2-decade range of curvatures. The luminance profile of the edge pattern was either sharp or blurred on a scale that varied over a range of almost 2 decades. The experiments with curved blurred stimuli can also be regarded as investigations of contrast discrimination in which a blurred bar is superimposed orthogonally upon a blurred edge. The discrimination thresholds for the blurred stimuli show substantial size invariance, which can be explained in terms of contrast discrimination and masking with orthogonally oriented patterns rather than in terms of curvature per se. No such size invariance is found with sharp stimuli. All results can be described by a simple model based only upon local contrast.