Portland State University. Department of Psychology
Gerald M. Murch
Date of Publication
Master of Science (M.S.) in Psychology
1 online resource (45 p.)
Previous attempts to adequately evaluate orientation-specific colored aftereffects (Mccollough Effects) have thus far been unsuccessful in yielding quantitative measures of relative strengths of the effects. Similarly, little success has been shown in previous attempts to establish what level of illumination is necessary in order to evoke the aftereffects. The present study sought to determine (a) whether threshold measurements could serve as adequate, quantitative dependent variables of the Mccollough Effects, (b) whether photopic illumination was necessary in order to evoke the aftereffect. It was predicted that the greater the number of inspection trials, the dimmer the illumination level could be in order for the aftereffects to first be detected. In addition, it was· predicted that the appearance of the test pattern would change markedly near the rod-cone break. The strength of the McCollough Effects, as a function of the number of inspection trials, was examined on subsequent scotopic and photopic threshold measurements in normal color-visioned subjects. All subjects were measured alternately on 10 ascending and 10 descending trials at specific times after being conditioned in "short" (15 min) and "long" (30 min) inspection trials, counterbalanced across subjects, with a 7-day interval between test trials. Overall, statistically insignificant results were achieved for both predictions; possible explanation of the results and changes in experimental design were discussed.
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Murphy, Marilyn, "Scotopic and photopic thresholds : a dependent variable for the McCollough effect" (1985). Dissertations and Theses. Paper 3529.