What is Illusion ?
Illusion
History of the illusion:
As indicated on the displays, the illusion has been developed independently in two laboratories, and was presented by both laboratories at the Society for Neuroscience conference in Washington, D.C., in November 2008.
I developed the effect as an extension of the illusions that Emily Knight, Zhong Lin Lu, and I presented at the May 2008 Best illusion of the year contest (here is a link to the pdf of the entry) and as an extension of our work on “feature blur” in the visual periphery.
Peter Meilstrup and Mike Shadlen presented their version of the illusion as part of a continuation of Shadlen and Movshon’s work on motion signals in the brain (specifically, in area MT of the visual cortex).
I developed the effect as an extension of the illusions that Emily Knight, Zhong Lin Lu, and I presented at the May 2008 Best illusion of the year contest (here is a link to the pdf of the entry) and as an extension of our work on “feature blur” in the visual periphery.
Peter Meilstrup and Mike Shadlen presented their version of the illusion as part of a continuation of Shadlen and Movshon’s work on motion signals in the brain (specifically, in area MT of the visual cortex).
Definition of Illusion:
i- According to " Voltaire" Everything's fine today, that is our illusion.
ii- According to "Socrates" A system of morality which is based on relative emotional values is a mere illusion, a thoroughly vulgar conception which has nothing sound in it and nothing true.
iii- According to "Friedrich Nietzsche" Love matches, so called, have illusion for their father and need for their mother.
Thus According to my study "Wrong Perception is called Illusion".
Types of Illusion:
1-Müller-Lyer illusion
2-Poggendorff illusion
3-Nacker cube illusion
4-Hering illusion
i- According to " Voltaire" Everything's fine today, that is our illusion.
ii- According to "Socrates" A system of morality which is based on relative emotional values is a mere illusion, a thoroughly vulgar conception which has nothing sound in it and nothing true.
iii- According to "Friedrich Nietzsche" Love matches, so called, have illusion for their father and need for their mother.
Thus According to my study "Wrong Perception is called Illusion".
Types of Illusion:
1-Müller-Lyer illusion
2-Poggendorff illusion
3-Nacker cube illusion
4-Hering illusion
1-Müller-Lyer illusion
All these theories had a common feature: they were attempts to explain the distortion in terms of the stimulus pattern without reference to its significance in terms of the perception of objects. There was, however, one quite different suggestion made by A. Thiéry (1896) that the distortions are related to perspective depth features. Thiéry regarded the Müller-Lyer arrows as drawings of such objects as a saw-horse, seen in three dimensions, with the legs going away from the observer in the acute-angled figure and towards him in the obtuse-angled figure. This suggestion has seldom been considered until recently, though the 'perspective theory' was described by R. H. Woodworth in 1938: 'In the Müller-Lyer figure the obliques readily suggest perspective and if this is followed one of the vertical lines appears farther away and therefore objectively longer than the other'. This quotation brings out the immediate difficulties of developing an adequate theory along these lines, for the distortion occurs even when the perspective suggestion is not followed up, for the figure generally appears flat and yet distorted; and there is no hint given of a modus operandi, or brain mechanism responsible for the size changes. An adequate theory following Thiéry's suggestion that perspective is somehow important must show how distortion occurs though the figures appear flat. It should also indicate the kind of brain mechanisms responsible.
Müller-Lyer arrows figure 1889. The most famous illusion: the outward-going 'arrow heads' produce expansion of the 'shaft' and the inward-going heads contraction. This was, however, left unexplained, and it is not clear why it should produce size changes without apparent changes of angle.
All these theories had a common feature: they were attempts to explain the distortion in terms of the stimulus pattern without reference to its significance in terms of the perception of objects. There was, however, one quite different suggestion made by A. Thiéry (1896) that the distortions are related to perspective depth features. Thiéry regarded the Müller-Lyer arrows as drawings of such objects as a saw-horse, seen in three dimensions, with the legs going away from the observer in the acute-angled figure and towards him in the obtuse-angled figure. This suggestion has seldom been considered until recently, though the 'perspective theory' was described by R. H. Woodworth in 1938: 'In the Müller-Lyer figure the obliques readily suggest perspective and if this is followed one of the vertical lines appears farther away and therefore objectively longer than the other'. This quotation brings out the immediate difficulties of developing an adequate theory along these lines, for the distortion occurs even when the perspective suggestion is not followed up, for the figure generally appears flat and yet distorted; and there is no hint given of a modus operandi, or brain mechanism responsible for the size changes. An adequate theory following Thiéry's suggestion that perspective is somehow important must show how distortion occurs though the figures appear flat. It should also indicate the kind of brain mechanisms responsible.
2-Poggendorff illusion
The Poggendorff illusion figure (1860). The straight line crossing the rectangle appears displaced.
3-Nacker cube illusion
FIG.(a) Necker cube. This is the most famous of many depth-ambiguous, figures. (When presented with no background it changes in shape with each reversal, the apparent back being larger than the apparent front face.) (b) Necker rhomboid. This is the original form, presented by L. A. Necker in 1832. The types of illusions which concern us here are, however, entirely different from either optical or sensory illusions. We may call these perceptual illusions. They arise from misinterpretation by the brain of sensory information. Several perceptual illusions were known to the ancient Greeks, but they have only been studied experimentally for just over a century. The first scientific description in modern times was a letter by a Swiss naturalist, L. A. Necker, to Sir David Brewster (Necker, 1832) describing how a rhomboid reverses in depth, sometimes one face appearing the nearer, sometimes another. Necker correctly noted that changes of eye fixation could induce this change in perception, but that it would occur quite spontaneously. This famous effect is generally illustrated with an isometric skeleton cube ( a) rather than Necker's original figure Perceptual reversals, or alternations (there can be several alternative perceptions) are not limited to vision. Repeated words, presented on an endless tape loop, give analogous auditory reversals (Warren and Gregory 1958 [REF 3]); A similar, even more striking effect, was noted by W. J. Sinsteden: that the rotating vanes of a windmill spontaneously reverse direction when it is not clear whether one is seeing the front or the back of the windmill (for references, see Boring, 1942). This effect is well shown by casting the shadow of a slowly rotating vane upon a screen, thus removing all information of which is the back and which the front. The shadow will also at times appear to expand and contract upon the plane of the screen. It is important to note that these effects are not perceptual distortions of the retinal image: they are alternative interpretations of the image, in terms of possible objects, and only one interpretation is correct.
4-Hering illusion
FIG. (a) Hering illusion (1861) The straight parallel lines appear bowed outwards. (b) Wundt's variant of the Hering illusion: the parallel lines appear bowed inwards (1896). Interest in the illusions became general upon the publication of several figures showing distortions which could produce errors in using optical instruments. This concerned physicists and astronomers a hundred years ago, when photographic and other ways of avoiding visual errors were not available. The first of the special distortion figures was the Poggendorff figure of 1860 . This was followed by the Hering illusion (1861); its converse being devised by Wundt much later, in 1896. The most famous illusion of all is the Müller-Lyer arrow figure. This was devised by F. C. Müller-Lyer and was first presented in fifteen variants (Müller-Lyer, 1889). This figure is so simple, and the distortion so compelling that it was immediately accepted as the primary target for theory and experiment. All sorts of theories were advanced: Wundt's eye movement theory (in spite of its inadequacy); that the 'wings' of the arrow heads drew attention away from the ends of the central line, or 'arrow shaft', to make it expand or contract; that the heads induced a state of empathy in the observer (though the distortion seems far too constant for such an explanation), that the distortion is a special case of a supposed general principle that acute angles tend to be overestimated and obtuse angles underestimated.