DISCRIMINABILITY IN LENGTH OF LINES IN THE MULLER-LYER FIGURE

Receiver-operating characteristics for the discriminability in the len gth of the lines of the Muller-Lyer figure were obtained by the rating method of detection theory. Six observers judged the shaft length of the lines of the figure with reference to the same standard line. Maxi mum-likelihood estimates of the index of discriminability, d', were a Linear function of the difference in the length of the Lines, but the functions did not pass through the origin because of a constant error of judgment. Because discriminability was determined by ROC analysis, the constant error could not be attributed solely to changes in criter ion placement; instead, it showed that the Muller-Lyer figure induced a change in the discriminability of the lines.