With all due respect, what you're asking about is pretty obscure. I had a three-hour graduate course in sensation and perception, and I had never heard of the McCollough effect until I read your post and googled it. If you're wondering whether it is safe to try as a lark, I wouldn't. If the aftereffect were to last for days, weeks, or months, it could be very disturbing . As for whether it can cause cancer, I seriously doubt it, but for more detailed information on the McCollough effect, I think you would need to speak to a true expert on it.
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