The terms optical illusion refer to all Illusion which misleads the visual Système human (since the eye until the Cerveau) and leads to a Perception deformed Réalité. The optical illusions can occur naturally or be created by specific visual easy ways which make it possible to highlight the Principe S of operation of the human visual system.

The illusion is an erroneous perception

The illusion results from a bad analysis by the visual system of information which comes from to him. This error of analysis can thus involve the perception of an object which is not present, contrary us to return " aveugle" with an object however present, to give us a distorted image of reality, etc

Thus, on the image of right-hand side, the boxes has and B of the drawing seem to be painted of two Teinte S of Gris different whereas actually, if one measures the Luminance on photography, both gray are perfectly identical. In this precise case, this example highlights the propensity of the visual system to compensate for the slow variations of luminosity.

A contrario , the Mirage S is not strictly speaking illusions. It is not a question of false a Interprétation Mental E of a reality but of the perception of a phenomenon which exists indeed: The tremor of the Air or the reflections of Eau due to heat is optical realities and not illusions, moreover one can keep the trace Photographique of it. The only illusion would consist in interpreting these images perceived like the turbid images of a Lac or a Mer.

Utility of the illusions for the cognitive Neurosciences

Developed or discovered illusions include phenomena like the Cube of Necker and the Grill of Hermann. To include/understand these phenomena is useful in order to include/understand what can seem limitations of the human system visual, but partly also results from produced phenomena Cognitif S themselves of the Natural selection: a hasty and sometimes false perception can be shown more adapted in term of survival than an exact analysis whose result would have come too late (Effet Tetris). It is the case when the cost of the error is weak when it is done on a side, and large when it is done other.

The physiological phenomena, like the residual images according to the plugging lights or an exposure prolonged of reasons, are the effects on the eye of a stimulation of a specific type - Luminosité, Inclinaison, Couleur, Mouvement,… the current Théorie S suppose that the stimulis have - after local treatment - neuronal ways dedicated to the visual cortex, a repeated stimulation of only some ways can make lose its reference marks with the optical system.

Cognitive illusions

The cognitive illusions are more interesting and well-known. Instead of showing a physiological cause they act with several levels of visual interpretation, the assumptions pre-formatted or “knowledge” is gotten mixed up. The cognitive illusions are commonly divided into ambiguous illusions, distorted illusions, paradoxical illusions or fictitious illusions. They often exploit the " hypothèses" formed by the visual system during the first stages of the visual treatment.

Ambiguous illusions

The ambiguous illusions are images or objects which undergo significant changes of appearance. Perception will alternate between interpretations which all will be perceived as valid but do not confirm only one representation. The Cube of Necker in is a well-known example.

Distorting illusions

The distorting illusions are most common, these illusions offer distortions of size, width or curve. They were easy to discover and are easily locatable. Much is physiological illusions, as the Illusion of the Coffee wall which exploits the first stages of the visual system in connection with the edges. Other distortions, like the illusions of convergent lines, are more difficult to compare to physiological or cognitive illusions. All the images which present prospect raw are many illusions. Visual judgments as the size are controlled by the prospect or other effects of depths and can easily be badly laid out.

Paradoxical illusions

The paradoxical illusions relate to the impossible objects, like the Triangle of Penrose or of the impossible staircases, as in work of Mr. C. Escher. The triangle is an illusion depending on a bad cognitive interpretation according to laquellles the adjacent edges must join.

Fictitious illusions

The fictitious illusions allow the perception of objects which are really not visible except for its observer, such as those induced by the Schizophrénie or the Drogue S Hallucinogène S.

Some examples of optical illusions

The known illusions are:

Relief

Following the invention of the Photography, one very quickly imagined apparatuses with two objective S able to fix side by side the images which each of the two eyes sees. It is the invention of the Stéréoscopie which knew a considerable passion in the years 1900. Their reading requires an optical system. There is however average to occur some; see this: Stereography and Car-stéréoscopie
L' Anaglyphe gets an illusion of relief thanks to a Filtre (optical).
With the invention of the Autostéréogramme, Jacques Ninio finds the means of suggesting the relief in absolutely plane images and without another artifice that light a strabisme.

The color

When a long time a coloured image is fixed, our receivers saturate, and by remanence, when one carries then the glance on a white surface, one sees it in the colors complementary to those which one fixed.

The optical illusion in art

In visual arts, various effects were tested in order to induce impressions or illusions at the spectator. Among those the Perspective , the Anamorphosis, the Arcimboldesque (Arcimboldo), the paradoxical Prospect (Escher), the Put in abyme, the Paving. COp art, with inter alia, Victor Vasarely, will seek an illusion of movement caused by violent one structured contrasts. Youri Messen-Jaschin uses lines of colors traced on materials playing the transparency, reproduce particularly subtle kinetic structures which connect abstracts it and the illusion on the one hand and a psychophysiologic demonstration of the movement on the other hand.

One can also announce the plays on the writing of certain words known under the name of Ambigramme S.

See too

Internal bonds

External bonds

  • Collection of optical illusions (often coloured)

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