Metacontrast functions were obtained for three subjects using forced-choice and magnitude-estimation response measures, and for a fourth subject using forced choice alone. The functions from these two measures were in every case U shaped and did not differ significantly from each other, even though the stimuli used for each measure differed slightly, and the forced-choice study was done three months after the magnitude-estimation study. Thus, U-shaped metacontrast functions are not artifacts of subjective response criteria. The relative merits of the subjective and objective response indicators as measures of metacontrast are discussed.
NAOMI WEISSTEIN, THOMAS JURKENS, and THERESE ONDERISIN, "Effect of Forced-Choice vs Magnitude-Estimation Measures on the Waveform of Metacontrast Functions," J. Opt. Soc. Am. 60, 978-980 (1970)