- geometric-optical illusion
- The term geometric-optical illusion is indebted to the Greek words geometria (land surveying) and opsis (seeing). It was introduced in or shortlybefore 1854 by the German physicist Johann Joseph Oppel (1815-1894) to denote a *visual illusion occurring specifically in association with a geometric structure or line drawing. A classic example of a geometric-optical illusion is the * Oppel-Kundt illusion, in which a distance divided by graduated lines appears to be longer than a similar, but undivided distance. Oppel's attention was drawn to this type of illusion after he noticed certain regularly recurring flaws in his students' drawings. Some other classic examples of the geometric-optical illusion are the * Müller-Lyer illusion, the * Poggendorff illusion, and the * Zöllner illusion. Many of these phenomena had been noticed - and employed intentionally - by philosophers, artists, and architects since ancient times, but it is Oppel who is commonly credited with having initiated the scientific study of these phenomena. Although the adjective optical may seem to suggest an involvement of the optics of the eye, geometric-optical illusions are commonly classified as * cognitive illusions (i.e. illusions arising as a consequence of the workings ofhigher-order cognitive processes).ReferencesOppel, J.J. (1854/1855). Ueber geometrischoptische Täuschungen. (Zweite Nachlese.) In: Jahres-Bericht des physikalischen Vereins zu Frankfurt am Main, 37-47.Oppel, J. (1856). Ueber geometrisch-optische Täuschungen. Poggendorffs Annalen der Physik und Chemie, 99, 466.Rutten, F.J.Th. (1929). Psychologie der waarnem-ing. Een studie over gezichtsbedrog. Thesis, University of Utrecht.Seckel, A. (2005). Super visions: Geometric optical illusions. New York, NY: Sterling Publishing Co.
Dictionary of Hallucinations. J.D. Blom. 2010.