Line intensity affects perceived shape.

A method for measuring the variation of one stimulus parameter with respect to another is applied to show how line intensity affects the perceived tilt of lines, internal angle of chevrons, and curvature of circular arcs. Perceived curvature increased with increasing line intensity, but analogous effects were found only for obtuse chevrons, not for acute ones, suggesting a limit to the range of orientations which contribute to the processing of curvature. The absence of a clear trend for tilted lines and acute angles highlights the specificity of the curvature findings. Explanations based on a computer model and other psychophysical and single-unit studies are examined.