TYCHO'S ILLUSION: HOW IT LASTED 400 YEARS,
AND WHAT THAT IMPLIES ABOUT HUMAN COGNITION
Target Article by Margolis on Cognitive Illusion

Abstract

This target article reports a case in which for a very long time the very best experts (Tycho and Kepler 400 years ago, Thomas Kuhn and many others in recent decades) have suffered an easily corrected illusion. It provides a striking counterexample to claims that cognitive illusions can be reasonably treated merely as effects that clever experimenters can elicit from naive or poorly motivated subjects, but otherwise as not really illusions. The present illusion is based on an apparent collision between the spheres of Mars and the sun in the "Tychonic" alternative to Copernicus in the early 17th Century. The perception of a collision permanently disappears when Tycho's own diagram is presented in a novel way. The illusion appears to come from an unconscious (hence not consciously noticed) mental rotation which is consistent with everyday habits of mind but flatly incompatible with the logic of the situation. This then produces the failure of even the very best experts to notice that what they are seeing in Tycho's diagram is something that is not there. However, once a person sees the cutout described in the article move (i.e., once the rotation becomes a physical rotation, not a mental rotation), the illusion disappears permanently. The present target article is the expanded version of a shorter summary that appeared in Nature (Margolis 1998); this fuller version is published in Psycoloquy so as to elicit Open Peer Commentary, to which the author will respond.

Keywords

References

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