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Katherine E.M. Tregillus, Yanjun Li, Stephen A Engel; McCollough world: A novel induction method for orientation-contingent color aftereffects. Journal of Vision 2019;19(10):72a. doi: https://doi.org/10.1167/19.10.72a.
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The McCollough Effect (ME) is a well-known visual illusion characterized by long-lasting color afterimages following adaptation to two color/orientation pairings. For example, viewing a red and black vertical grating alternating with a green and black horizontal grating causes achromatic vertical and horizontal patterns to appear greenish and reddish, respectively. Though the ME can be induced with only a few minutes of exposure, adapting to gratings for longer durations is challenging. Here we propose a method that allows participants to adapt for hours, resulting in very strong, long-lasting afterim-ages. To create this “McCollough world,” participants viewed videos through a head-mounted display (HMD) with an attached camera. Frames from the camera were filtered in the Fourier domain to limit energy to a narrowband of orientations and then were binarized. Vertical and horizontal filters were paired with red and green, and the color/orientation pairs alternated every 2 sec. The images appeared as tiger-stripe like representations of the world. Content was difficult to recognize, but illusory contours and motion allowed recognition of the gist of many scenes. Participants lived in this McCollough world for two hours. We measured the magnitude of afterimages by having observers view physically achromatic gratings and adjust the color of the whitish stripes to the opposite color, nulling the aftereffect. The nulling task was performed immediately after adaptation, again 15 minutes later, and again 1 hour after adaptation. In all 3 participants tested, aftereffects were substantially larger (mean = ~50%) than those produced by a 10 min “classic” ME induction. This was the case at all three timepoints tested. All participants also reported afterimages after removing the HMD, where vertical and horizontal edges viewed in the real world appeared colorful. Our method allows participants to adapt for many hours at a time, producing strong aftereffects amenable to study with neuroimaging.
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