Virsu, V. (1971b). Underestimation of curvature and task dependence in visual perception of form. Perception and Psychophysics, 9(3B), 339-342.

Perceived curvatures of circular arcs were compared with those of circles. The length and orientation of the arcs varied. In all cases the curvatures of the arcs were underestimated, and the error was a decreasing exponential function of arc length. The results are consistent with the notion that tendency (effect readiness) to perform rectilinear eye movements produces underestimation of curvature. The results discredited the explanation of the "Gibson normalization effect" as an instance of increase in perceptual accuracy. The overestimation of curvature found in earlier studies was interpreted as resulting from an inappropriate perceptual task and uncontrolled effects of illusions of extent.