Margolis: TYCHO'S (COGNITIVE) ILLUSION The target whose abstract article follows below has just appeared in both (1) PSYCOLOQUY, a refereed journal of Open Peer Commentary sponsored by the American Psychological Association, and, (2) in a shorter version, in NATURE. Qualified professional biobehavioral, neural or cognitive scientists are hereby invited to submit Open Peer Commentary on it. Please email for Instructions if you are not familiar with format and acceptance criteria for PSYCOLOQUY commentaries (all submissions are refereed). To submit articles and commentaries or to seek information: EMAIL: psyc(a)pucc.princeton.edu URL: http://www.princeton.edu/~harnad/psyc.html http://www.cogsci.soton.ac.uk/psyc RATIONALE FOR SOLICITING COMMENTARY: This target article is the expanded version of a shorter summary that has just appeared in Nature (Margolis 1998); the full version is published in PSYCOLOQUY so as to elicit Open Peer Commentary, to which the author will respond. It describes a striking case of a cognitive illusion that has fooled an expert community for a very long time (400 years!). With no exceptions, the leading astronomers of Kepler's time and the leading experts of the history of science in our time have believed that in a world of solid spheres, there would be a collision between Mars and the sun in the Tychonic system. Detailed arguments by Kuhn and many others have been based on the imagined effects of this collision (in prompting the abandonment of belief in the spherical orbits, even in prompting Copernicus to abandon the Earth as center of the world). But the illusion vanishes permanently once Tycho's own diagram is presented in a novel way. None of the various arguments to the effect that cognitive illusions are not really illusions, or that they occur only with trick questions, or only when nothing important to the judge is at stake, etc., seem to apply here. Proponents of such objections may wish to argue otherwise, however, and are invited to contribute their peer commentary. Insights that can be drawn from this episode extend to a number of other topics of current interest. The case seems to provide a striking example of the interaction between affect and logic in persuasion. Tycho's system was seen then and now as somehow a great improvement over Ptolemy's, although logically it is distinguished from Ptolemy's by very little except that it looks Copernican, which provides some support for Zajonc's "primacy of affect" claim. Mental rotation seems essential for the illusory collision, but that rotation cannot be "seen", because once it is concretely visualized (as it is when converted into a physical rotation), the illusion disappears. So something like blindsight with respect to mental rotation seems to be involved here; the case may prove relevant to the debates over mental imagery, whose participants are likewise invited to contribute commentaries. In general, the case provides a striking illustration of the power of habits of mind to dominate mere logic. ----------------------------------------------------------------------- psycoloquy.98.9.32.cognitive-illusion.1.margolis Thu Jul 16 1998 ISSN 1055-0143 (33 parags., 20 refs., 6 figs., 5 notes, 605 lines) PSYCOLOQUY is sponsored by the American Psychological Association (APA) Copyright 1998 Howard Margolis TYCHO'S ILLUSION: HOW IT LASTED 400 YEARS, AND WHAT THAT IMPLIES ABOUT HUMAN COGNITION Howard Margolis Harris School Public Policy Studies University of Chicago 1155 E60th Street Chicago IL 60637 773-702-0867 773-702-0926 (fax) hmarg(a)uchicago.edu http://www.harrisschool.uchicago.edu/Tycho.html 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: blindsight, cognitive illusion, mental image, persuasion, psychology of science. http://www.princeton.edu/~harnad/psyc.html http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/1998.volume.9/psyc.98.9.32.co… gopher://gopher.princeton.edu/11/.libraries/.pujournals news:sci.psychology.journals.psycoloquy