A comparison of human gaze patterns on illusions before and after a simple color manipulation is presented. The optical illusions used include Fraser’s illusion, Akiyoshi Kitaoka’s Rotating Snakes, and the Necker cube. All of these images were then modified in an attempt to render the illusion non-illusory. The images are then shown to 8 participants, split into two groups of 4. Each group will...

The Müller-Lyer figure is a famous optical illusion where we think two line segments have different lengths, although the lengths are in fact equal. If our brains generate optical illusions, we might ask ourselves the question whether moral illusions can exist, how we can detect them and what we can learn from them. In this article we argue that speciesism – the difference in moral status betwe...

We investigated four geometric optical illusions (Zöllner, Müller-Lyer, Ponzo and Delboeuf), plus illusory contour/border induction (Kanizsa) and depth in random-dot stereograms (Julesz). Two different display conditions were compared: equiluminance with chromaticity contrast and heteroluminance without chromaticity contrast. The main results are as follows. (1) The strength of the four geometr...

! Optical illusions are images that are visually perceived differently than how they actually appear in reality. These images can be very entertaining, but also very deceiving. Optical illusions are caused by either an error with oneʼs visual sense or an error of intellect. This " error of intellect " occurs when the visual senses correctly interprets an image, but the mindʼs imagination, false...

The filled/empty illusion (Oppel-Kundt) is one of the oldest geometrical-optical illusions, but the determinants of the illusion are not yet sufficiently understood. We studied magnitude of the illusory effect as a function of the height of vertical strokes subdividing a spatial extension of fixed length, using the psychophysical standard-variable matching paradigm. For vertical strokes shorter...

The idea of a largely segregated processing of color and form was initially supported by observations that geometric-optical illusions vanish under isoluminance. However, this finding is inconsistent with some psychophysical studies and also with physiological evidence showing that color and luminance are processed together by largely overlapping sets of neurons in the LGN, in V1, and in extras...

The term geometrical–optical illusions was coined by Johann Joseph Oppel (1815–1894) in 1855 in order to distinguish spatial distortions of size and orientation from the broader illusions of the senses. We present a translation of Oppel’s article and a commentary on the material described in it. Oppel did much more than give a name to a class of visual spatial distortions. He examined a variety...