Differences between the geometrical properties of simple configurations and their visual percept are called geometrical-optical illusions. They can be differentiated from illusions in the brightness or color domains, from ambiguous figures and impossible objects, from trompe l'oeil and perspective drawing with perfectly valid views, and from illusory contours. They were discovered independently...

Evolution’s view Many optical illusions have evolutionary survival value, and thus many are hard-wired. We can train ourselves to be less influenced by such illusions, but we can’t eliminate them entirely. The analogous errors of the cognitive system are what I call cognitive illusions (or distortions in orthodox cognitive behavioural therapy literature). Overgeneralization is a common cognitiv...

Subjective estimates of lengths or areas in the visual field depend on the visual contents of the estimated space (filled/empty or Oppel-Kundt illusion). We studied the dependence of this phenomenon on the presentation mode (white on black vs. black on white background), and on the figure/ground contrast. We found, as expected, overestimation of the filled part of the figure for both contrast p...

Most research on the Poggendorff illusion has focused on explaining the effect. Poggendorff illusion, it doesnt naturally predict the reduction in the illusion.dicted the perceived angle in a modified Poggendorff illusion task with an extra thick bar. The concept of disinhibition employed in the model is general enough. A new explanation for the Poggendorff illusion. The application of this exp...

Abstract. Looking back over 15 years of demonstrating visual phenomena and optical illusions on the Internet, I will discuss two major topics. The first concerns the methodology used to present interactive visual experiments on the web, with respect to (a) wide accessibility, ie independent of browser and platform, (b) capable and elegant graphic user interface, (c) sufficient computational pow...

A subdivided path in the visual field usually appears longer than an empty path of the same length. This phenomenon, known as the filled/empty or Oppel-Kundt illusion, depends on multiple properties of the visual stimulus, but the functional dependences have not been yet precisely characterized. We studied the illusory effect as a function of its two main determinants, the height of vertical st...

The Windows program Visuelle Welt allows the demonstration of various visual phenomena such as geometrical-optical illusions, subjective contours, apparent movement, and Gestalt principles. One of the program's most interesting features is that the illusion-inducing context can be switched off, and in addition for many phenomena parameters can be varied interactively.

The Beuchet Chair is a powerful and highly popular optical illusion. The illusion involves two reasonably large pieces of apparatus: an oversized chair seat and four normal-sized chair legs. When properly arranged and viewed from a precise location, a person standing on the seat appears to be much smaller than they actually are. Although compelling, the illusion is relatively challenging and ex...