Abstract

Optical blur has a wide range of effects on localization performance, depending on stimulus configuration and task. Furthermore, in some tasks, the efficiency of human observers, relative to an appropriate ideal observer, actually increases with increasing blur.¹ To explore this puzzle, separation discrimination was measured for 5'-long line segments as a function of base separation, luminance, and level of Gaussian blur. Blur and luminance had large effects at small base separations and relatively small effects at large separations. The data were also compared with the predictions of an ideal observer that was limited only by quantal fluctuations and the preneural factors up to the level of the photopigment in the photoreceptors.¹ The predictions matched the data for base separations up to those yielding optimal sensitivity. However, at larger base separations, threshold increased and the effects of blur disappeared. Thus, at large separations relative efficiency is higher for blurred stimuli.

© 1989 Optical Society of America