Wundt illusion

Wundt illusion

The Wundt illusion is an optical illusion that was first described by the German psychologist Wilhelm Wundt in the 19th century. The two red vertical lines are both straight, but they may look as if they are bowed inwards to some observers. The distortion is induced by the crooked lines on the background, as in the Orbison illusion. The Hering illusion produces a similar, but inverted effect.

Vertical-horizontal illusion

the vertical–horizontal illusion

Another variant of the Wundt illusion is the Horizontal–Vertical Illusion, introduced by Wundt in 1858. The two intersecting lines are equal in length although the vertical line appears to be much longer. The horizontal line needs to be extended up to 30% to match the perceptual length of the vertical line. This is not confined to simple line drawings, as this can also be seen in buildings, parking meters, as well as other things viewed in a natural setting.

Optical illusions (list)
Illusions	Afterimage Ambiguous image Ames room Barberpole Bezold Café wall Checker shadow Chubb Cornsweet Delboeuf Ebbinghaus Ehrenstein Flash lag Fraser spiral Gravity hill Grid Hering Impossible fork Jastrow Lilac chaser Mach bands McCollough Müller-Lyer Necker cube Orbison Penrose stairs triangle Peripheral drift Poggendorff Ponzo Rubin vase Sander Schroeder stairs Spinning Dancer Ternus Vertical–horizontal White's Wundt Zöllner
Popular culture	Op art Trompe-l'œil Ascending and Descending (drawing) Waterfall (drawing) Spectropia (book)
Related	Auditory illusions Tactile illusions Temporal illusion

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