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Seeing Red and Green: The McCollough Effect

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Seeing Red and Green: The McCollough Effect

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    1. Seeing Red and Green: The McCollough Effect

    2. 2 After Effects Occur in all modalities Most last only seconds An exception: The McCollough Effect - an orientation-contingent color aftereffect. Source: McCollough, Celeste (1965). Color adaptation of edge-detectors in the human visual system. Science, 149, 9, 1115­1116.

    3. 3 Do you see any colors? No… Do you see any depth in this figure? Yes, diamond atop diamond atop rectangle Do you see any diagonals? Yes, but they are not “really” there. Do you see any colors? No… Do you see any depth in this figure? Yes, diamond atop diamond atop rectangle Do you see any diagonals? Yes, but they are not “really” there.

    4. 4 We’re going to watch a slide show for ten minutes Bad news: you’re going to be tested on this Good news: it’s an easy test We’re going to watch a slide show for ten minutes Bad news: you’re going to be tested on this Good news: it’s an easy test

    5. 5

    6. 6 Anything happening here? Should be no effectAnything happening here? Should be no effect

    7. 7 Better luck this time?Better luck this time?

    8. 8

    9. 9 Better luck this time? Yes, a big effectBetter luck this time? Yes, a big effect

    10. 10 What is going on with the McCollough Effect? It’s like a regular color aftereffect, except It’s contingent on retinal edge orientation (i.e. depends on the pairing of the vertical lines with the green color and the horizontal lines with the red color but it can be induced with different stimuli) It does not depend on precise fixation (while adapting you can move your eyes away from the center of the slide and still get the effect) Normally doesn’t transfer between eyes It lasts a long time (recall that regular afterimages last only a minute or less)

    11. 11 Simple Color Aftereffects Last a few seconds and depend on precise fixationLast a few seconds and depend on precise fixation

    12. 12

    13. 13 Yes, it lasts days, even weeksYes, it lasts days, even weeks

    14. 14 Reorganize into a flat set of nested boxes, so that the diagonals disappear, and the colors vanish too!Reorganize into a flat set of nested boxes, so that the diagonals disappear, and the colors vanish too!

    15. 15 Explaining the McCollough Effect Opponent processes Subsystems pitted against one another in dynamic equilibrium (such as opposed muscle pairs) Fatiguing half of an opponent pair yields aftereffects (rising arm effect) Double opponent cells How do we perceive millions colors from 3 cones? Transform 3D information into a 2D plane with luminance held constant (the cie plane). The most saturated colors are on the periphery of the plane and the least saturated are in the center Blue-Yellow and Red-Cyan axes define opponent colors and Afterimages

    16. 16 Double Opponent Process Cells

    17. 17 Explaining the McCollough Effect Functional Theory (Dodwell and Humphrey, 1990) Why pair color with orientation? An adaptation system with statistical properties finds a neutral point (i.e. we define light vs dark by computing the mid point between the lightest and darkest signal) Changes occur very slowly because of all the data accumulated over time In the real world there is no correlation between edge and color A strong discrepancy (a signal that correlates vertical with green, for example) will create a new neutral point

    18. 18 More reading: Source: McCollough, Celeste (1965). Color adaptation of edge-detectors in the human visual system. Science, 149, 9, 1115­1116. Sacks, Oliver (1997) Island of the Colorblind and Cycad Island Palmer, Steve (1999). Vision Science. Dodwell, Peter, & Humphrey, G. Keith (1990). A functional theory of the McCollough effect. Psychological Review, 97, 1, 78-89.

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