Date of Award


Document Type


Degree Name

Master of Science (M.S.) in Psychology



Physical Description

1 online resource (xi, 60 leaves)


Color vision, After-images




The McCollough Effect is an orientation specific colored aftereffect. That is, following prolonged viewing of a vertical grid on orange ground alternated with a horizontal grid on blue ground, a yellow-orange hue is perceived on an achromatic horizontal grid, and a bluish hue on a vertical grid. McCollough suggested that the colored aftereffect may depend upon color adaptation of a population of neural elements specific to colored edges of a particular orientation. Accordingly vertical edge detectors sensitive to orange adapt during inspection such that when vertical edges are presented on an achromatic ground only those non-adapted color-line detectors respond creating the perception of blue. Similarly, horizontal edge detectors specific to blue adapt such that response to achromatic edges creates the perception of yellow-orange. In a subsequent study McCollough and Clark used left and right diagonal inspection patterns and observed that the aftereffect of orange and right diagonal was influenced by the left diagonal color that was alternated with it. The aftereffect of orange right diagonal tended toward blue when the orange stimulus was alternated with a blue left diagonal stimulus pattern and tended toward green when the orange stimulus was alternated with a green left diagonal pattern. On the basis of the color coded edge detector theory McCollough and Clark suggested the effect was induced by wavelength adaptation of wavelength sensitive edge detectors which may influence the hue of the• aftereffect on the orthogonal test pattern. A test of McCollough's model of color coded edge detectors was made by presenting a colored field (no lines) to S before the presentation of the color-line stimulus. If wavelength and edge stimuli were processed by a population of neural elements sensitive to both, then the aftereffect would not be affected by the presentation of an unlined color field. If color and line stimuli were processed separately, then the "effective" color component of the lined stimulus pattern would be that portion of the spectrum not stimulated by the preceeding color field. The color of the aftereffect would be approximately complementary to the non-adapted population of color receptors stimulated by the lined inspection pattern. In the experiment 28 college juniors observed two inspection conditions. In condition 1 orange vertical alternated with blue horizontal and the aftereffect created was measured via a colorimeter. The same stimulus patterns were employed in condition 2 where each was preceeded by a plain color field that stimulated a portion of the spectrum illuminated by the following lined stimulus. The aftereffect observed was compared with the aftereffect on condition 1. Color matches were measured by three photometer readings indicating percent transmittance of red, blue, and green in each match. These readings were translated into CIE x, y coordinates and the means plotted on a chromaticity diagram. Statistical analysis of the data indicated that the color matches in condition I and condition 2 were significantly different and varied as predicted. While McCollough and Clark attributed the variation in the hue of the colored aftereffect to the relative spectral properties of the lined inspection patterns employed in their experiment, the present study shows that the results may be due to the state of color adaptation resulting from the preceeding stimulus pattern. The adapting color stimulus is not necessarily a lined color pattern. It may indeed be a plain color field. The results suggest that the colored line-contingent aftereffect is created by at least two levels in the visual system: color receptors independent of slope analysers. The color coded edge detector model is not adequate to account for the McCollough Effect.


Portland State University. Dept. of Psychology

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