The effect of lightness contrast, tachistoscopic duration and fundus pigmentation on the magnitude of the Mueller-Lyer illusion.

ABSTRACT Mueller‐Lyer figures were presented tachistoscopically in illuminant C in four experiments which explored the effects of viewing time (500, 1500, 4500 and 9000 msec), contrast level (1.5 black/, 5 gray/, 7.5 light gray/ each on 9.5 white/ background) and fundus pigmentation on the magnitude of illusion. Significant interactions of contrast level and viewing time were evident. Results further indicate density of fundus pigmentation to be related significantly to illusion magnitude at the shortest viewing time, with more darkly pigmented Ss yielding a significantly smaller illusion than lightly pigmented Ss sampled from a white population. Illusion magnitude at a reduced viewing time would seem to be a function of absolute contrast.