The Kundt illusion, sometimes referred to as the Kundt partition, was described by him 98 years ago.1 Its existence has since then been generally accepted, but in my opinion has never, until the present time, been adequately explained. Kundt (1839-1894), a native of Mecklenburg, was not an ophthalmologist but a distinguished physicist, and, so far I can ascertain, published no other paper on vision. He was professor of physics successively in Zürich, Würtzburg, Strassburg, and finally after 1887, at Berlin University.
The Kundt illusion consists in the perceiving of the temporal half as shorter than the nasal half of a horizontal line viewed monocularly and kept at right angles to the line of sight at the point of bisection. Because of this illusion, when with the aid of only one eye, an attempt is made to bisect a horizontal line kept centered at right angles to the line of
VERHOEFF FH. The Kundt and the Tschermak-Seysenegg Illusions: Both Explained by Angle Alpha and the Pin-Hole Camera. Arch Ophthalmol. 1961;66(3):347–352. doi:10.1001/archopht.1961.00960010349010
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