Search results for "Optical illusion"
showing 10 items of 19 documents
Titchener's T with flanks.
2018
Abstract Flanks were added to Titchener's (1901) T-illusion figure to test its susceptibility to context stimuli. The addition of a second divided line yielded H-type figures, and the addition of a second undivided line, +-type figures. The lengths of the Ts' undivided lines was expected to be overestimated relative to the lengths of the divided lines, when all lines were about equally long, and the illusion was expected to become smaller when one or two gaps had been introduced between the lines. Results conformed to the predictions. The amount of illusion was larger for the no-gap H than the T, and was almost annihilated with the two-gaps H, with 3 out of 14 observers showing an inverse r…
On the interpretation of optical illusions.
1973
If excited by stimuli adjacent in space and time, the optical system frequently perceives illusions in the form of apparent movements. These effects may be attributed to the dynamic properties of the retinal nerve nets. On the basis of a specific psychophysical experiment the mechanism underlying the generation of optical illusions is interpreted by the methods of systems theory and its use in systems analysis is discussed. It is shown that for the perception of apparent movements the transit times of the signals in the dendrites are particularly important.
Visual aftereffects and sensory nonlinearities from a single statistical framework
2015
When adapted to a particular scenery our senses may fool us: colors are misinterpreted, certain spatial patterns seem to fade out, and static objects appear to move in reverse. A mere empirical description of the mechanisms tuned to color, texture, and motion may tell us where these visual illusions come from. However, such empirical models of gain control do not explain why these mechanisms work in this apparently dysfunctional manner. Current normative explanations of aftereffects based on scene statistics derive gain changes by (1) invoking decorrelation and linear manifold matching/equalization, or (2) using nonlinear divisive normalization obtained from parametric scene models. These p…
Titchener's T in context 2 - Symmetric patterns of two Ts.
2019
Abstract Patterns of two Ts, materializing different symmetry groups, were used to explore conditions that would lead to a modulation of the typically observed overestimation of the length of a T's undivided line relative to its divided line. Observers either had to compare the lengths of the lines of one or the other of the Ts in a pattern, or noncorresponding lines between the two Ts. For both tasks alike, the T-illusion was found to be markedly greater with twofold mirror-symmetric 2-T patterns than it usually is with individual Ts. A control experiment suggested that the effect was probably due to the collinearity of the two Ts' undivided lines in these patterns rather than the addition…
100 Years of Benham's Top in Colour Science
1995
For 100 years Benham's top has been a popular device demonstrating pattern-induced flicker colours (PIFCs). Results of early and recent investigations on PIFCs are reported and show that the phenomenon originates in phase-sensitive lateral interactions of modulated neural activity in the retina followed by additional spatial interactions in the visual cortex behind the locus of binocular fusion. Colour matches with normal colour stimuli indicate that S/(M + L) opponent neurons are involved. Dichromats do not find matching stimuli for all PIFCs. PIFCs may become useful in medical diagnosis. The phenomenon is interpreted as a side effect of a neural mechanism providing colour constancy under…
Paradox lost: variable colour-pattern geometry is associated with differences in movement in aposematic frogs
2014
Aposematic signal variation is a paradox: predators are better at learning and retaining the association between conspicuousness and unprofitability when signal variation is low. Movement patterns and variable colour patterns are linked in non-aposematic species: striped patterns generate illusions of altered speed and direction when moving linearly, affecting predators' tracking ability; blotched patterns benefit instead from unpredictable pauses and random movement. We tested whether the extensive colour-pattern variation in an aposematic frog is linked to movement, and found that individuals moving directionally and faster have more elongated patterns than individuals moving randomly and…
The Oppel-Kundt Illusion and Its Relation to Horizontal-Vertical and Oblique Effects.
2021
The Oppel–Kundt illusion consists in the overestimation of the length of filled versus empty extents. Two experiments explored its relation to the horizontal-vertical illusion, which consists in the overestimation of the length of vertical versus horizontal extents, and to the oblique effect, which consists in poorer discriminative sensitivity for obliquely as opposed to horizontally or vertically oriented stimuli. For Experiment 1, Kundt’s (1863) original stimulus was rotated in steps of 45° full circle around 360°. For Experiment 2, one part of the stimulus remained at a horizontal or vertical orientation, whereas the other part was tilted 45° or 90°. The Oppel–Kundt illusion was at its …
Visual illusions and the control of children arm movements.
2001
The aim of the present study was to determine whether children like adults (Gentilucci M, Chieffi S, Daprati E, Saetti MC, Toni I. Visual illusion and action. Neuropsychologia 1996;34:369-76; Gentilucci M, Daprati E, Gangitano M, Toni I. Eye position tunes the contribution of allocentric and egocentric information to target localisation in human goal directed arm movements. Neurosci Lett 1997;222:123-6) are influenced by visual illusions when they transform visual information in motor command. Children and adults pointed to a shaft extremity of the Müller-Lyer configurations, as well as to an extremity of a control configuration. Movements were executed in two experimental conditions. In th…
Perception of illusory surfaces and contours in goldfish
2007
Goldfish(Carassius auratus)were trained to discriminate triangles and squares using a two choice procedure. In the first experiment, three goldfish were trained with food reward on a black outline triangle on a white background, while a black outline square was shown for comparison. In transfer tests, a Kanizsa triangle and a Kanizsa square were presented, perceived by humans as an illusory triangle- or square-shaped surface of slightly higher brightness than the background. The choice behavior in this situation indicates that goldfish are able to discriminate between both figures in almost the same way as in the training situation. In control experiments goldfish did not discriminate betwe…
Color illusions also deceive CNNs for low-level vision tasks: Analysis and implications.
2019
The study of visual illusions has proven to be a very useful approach in vision science. In this work we start by showing that, while convolutional neural networks (CNNs) trained for low-level visual tasks in natural images may be deceived by brightness and color illusions, some network illusions can be inconsistent with the perception of humans. Next, we analyze where these similarities and differences may come from. On one hand, the proposed linear eigenanalysis explains the overall similarities: in simple CNNs trained for tasks like denoising or deblurring, the linear version of the network has center-surround receptive fields, and global transfer functions are very similar to the human …