SIGNAL-DETECTION ANALYSIS OF THE MULLER-LYER AND THE HORIZONTAL-VERTICAL ILLUSIONS

Perceptual error in the Muller-Lyer and the Horizontal-Vertical illusi ons was quantified using nonparametric signal-detection measures of se nsitivity and response bias. Sensitivity scores were positively relate d to signal strength with the greatest values observed for the stronge st signals. Sensitivity at each signal strength did not differ between the two illusions. Response-bias scores were inversely related to sig nal strength, with the most conservative biases observed for the stron gest signals. Response biases for each signal strength were significan tly more conservative for the Horizontal-Vertical than for the Muller- Lyer illusion.