Discrimination of contour curvature: data and theory.

Visual discrimination of contour curvature was investigated using stimuli having a single point of maximum curvature and a continuous derivative. Curvature discrimination as a function of mean curvature could be described by a power law with an exponent averaging 1.57. Data were also gathered as a function of line width, stimulus orientation, and retinal eccentricity. Finally, masking experiments provided evidence that the mechanisms responsible for curvature discrimination were both orientation and spatial-frequency selective. The data are well fitted by theoretical results derived from a line-element model that has recently been applied to spatial-frequency discrimination.