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CerebralDatabank McCollough Effect Tester

This is quite an interesting effect because, unlike a simple afterimage, this one lasts a long time. As with all our services, by using this site, you agree to the Terms of Service.

From Wikipedia:

The McCollough effect is a phenomenon of human visual perception in which colorless gratings appear colored contingent on the orientation of the gratings. It is an aftereffect requiring a period of induction to produce it. For example, if someone alternately looks at a red horizontal grating and a green vertical grating for a few minutes, a black-and-white horizontal grating will then look greenish and a black-and-white vertical grating will then look pinkish. The effect is remarkable because, although it diminishes rapidly with repeated testing, it has been reported to last up to 2.8 months when exposure to testing is limited.

The effect was discovered by American psychologist Celeste McCollough in 1965.

Easily experience this effect yourself with this simple test! Read the instructions before you begin. Also, make sure your browser is not significantly changing the color scheme of this page (e.g. from a force dark mode feature, from a night mode/warm color shift feature, etc.).


  1. Stare at the center of the test image (the black-and-white one).
  2. Click the "Show induction images" button. You will be repeatedly shown the two induction images alternately. Stare at the center of the image area, even as the image changes. You are allowed to move your eyes a little, but keep looking generally at the center.
  3. After approximately 5 minutes, click the "Show test image" button. The vertical lines will appear to have a red tint and the horizontal lines will appear to have a green tint (this is the same black-and-white image from before). This effect may last for a short or long time, depending on how long you stared at the induction images. If you do not experience the effect after approximately 10 minutes of staring at the induction images, use caution when trying for longer periods of time; the effect may last for months.
  4. That's it! Try viewing the test image later in the day to see if the effect still persists. If you looked at the induction images long enough, and didn't look at them too much afterwards, you may be able to open this page the next day's morning and see that the effect is still there!
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