Circular contour frequency in shape discrimination.

Circular contour frequency (the number of radial cycles per degree of unmodulated contour length measured in degrees of viewing angle) is an important factor in determining the deformation threshold of radial frequency (RF) patterns. Radial deformation thresholds were closely matched at a given circular contour frequency regardless of RF or radius. Our results suggest that two separate mechanisms may be involved in determining radial deformation thresholds. First, for low RFs, our results support a model of shape discrimination in which global integration occurs across all modulation cycles of an RF pattern. Second, for higher RFs, our data suggest that threshold may be determined by visual integration only over a limited segment of the RF pattern.