visual phenomena

The notorious Frankfurter Illusion
 

Is it a eurocentric bias on the visual that the majority of constructivist works start out with optical illusions? I am not sure. But be it as diverse personæ as von Foerster, Watzlawick, Maturana & Varela, or even Francis Crick—Berger & Luckman are an exception—, optical illusions serve as a stunning starter for their arguments. Me personally, I am a downright fanboy of illusions of all kind, hence I am of the opinion, that Alan Sokal’s warning to the social sciences and humanities—not to use metaphors which are way more complicated to understand than the phenomena you want to illustrate by their use—does not kick in here. Although the phenomena in question may have quite complex basis’ or even reasons unknown. Because of their immediacy, almost everybody can experience the phenomena ad hoc, I take optical illusions to hold immense argumentative and didactical value for all things constructivist. Now,
Michael Bach collected 72 Optical Illusions & Visual Phenomena on his website and renders them masterfully—especially in this respect online technology has at least one great advantage over printed matter on paper: illusions depending on the moving image can be demonstrated:
 

These pages demonstrate visual phenomena, and “optical” or “visual illusions”. The latter is more appropriate, because most effects have their basis in the visual pathway, not in the optics of the eye. […]
 

“Optical illusion” sounds pejorative, as if exposing a malfunction of the visual system. Rather, I view these phenomena as bringing out particular good adaptations of our visual system to standard viewing situations. These adaptations are “hard-wired” in our brains, and thus under some artificial manipulations can cause inappropriate interpretations of the visual scene. As Purkinje put it: “Illusions of the senses tell us the truth about perception” (cited by Teuber, 1960).
 

Don’t distress yourself if you don’t see the effect described, even if trying carefully. For many illusions, there is a small percentage of people with perfectly normal vision who just don’t see it, for reasons unknown.

Am I allowed to cheaply capitalize on the above? … The small percentage of people who do not see the empirical world at all, but illusions and figments of their own exclusively, are called politicians and bureaucrats.

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