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Howard S. Hock, Lee A. Gilroy; A common motion mechanism for first- and second-order stimuli. Journal of Vision 2002;2(7):395. doi: https://doi.org/10.1167/2.7.395.
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The independence of first-order, luminance-defined motion, and second-order, texture-defined motion was tested in three apparent motion experiments. In Experiment 1, a uniform square was presented against a uniform luminance background, and to its left, a checkerboard square was presented against a checkerboard background with the same average luminance. Motion can be perceived between the two squares when the luminance of the uniform square and the contrast of the checkerboard square are simultaneously changed in opposite directions. Evidence was provided for the inter-changeability of luminance and contrast changes: As the size of luminance and contrast changes were varied, the likelihood of motion being perceived between the uniform and checkerboard square was similar to the likelihood of it being perceived between two uniform squares with the same luminance changes and between two checkerboard squares with the same contrast changes. In Experiment 2, the perception of motion between two checkerboard squares due to changes in their contrast could be eliminated by counteracting the change in contrast for one of the checkerboards with a change in average luminance in the opposite direction (and vice versa). Experiment 3 provided evidence against changes in the location with the most salient element as a factor in the perception of luminance-to-texture motion: Motion was perceived between a uniform square and a checkerboard square even though the most salient square always remained at the same location. All of the above were observed at temporal frequencies for which attentional tracking was not possible. Conclusion: There is a common mechanism for the perception of apparent motion for first- and second-order stimuli that responds to counter-changing activation at nearby spatial locations, regardless of whether the activation changes are the result of changes in luminance or changes in texture contrast.
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