Several theoretical models for the prediction of liminal contrast are studied. One model that employs the known excitation and inhibition spread functions of the eye accurately predicts, at 10 mL, thresholds for circular targets, sine waves, and rectangles, including the line as a special case. Semiempirically, this model is extended to include thresholds at low light levels.
G. H. KORNFELD and W. R. LAWSON, "Visual-Perception Models," J. Opt. Soc. Am. 61, 811-820 (1971)