Contrast thresholds—measured with dots and Landolt rings—are given as a function of object size and brightness for 31 observers. The desirability of presenting upper and lower limiting threshold curves is pointed out. Differences with the experiments of Blackwell are discussed. The influence of training is shown to be negligible.
J. J. Vos, A. LAZET, and M. A. BOUMAN, "Visual Contrast Thresholds in Practical Problems," J. Opt. Soc. Am. 46, 1065-1065 (1956)