Difference between revisions of "Lilac chaser" - New World Encyclopedia

Latest revision as of 01:40, 26 October 2022

Stare at the center cross for at least 30 seconds to experience the three phenomena of the illusion.

Lilac chaser is a visual illusion, also known as the Pac-Man illusion, that spread across the Internet in 2005. Lilac chaser is very similar to phi phenomenon, and consists of 12 lilac (or pink or magenta-like), blurred disks arranged in a circle (like the numbers on a clock), around a small, black, central cross on a gray background.

The apparent movement of the lilac chaser and similar phi phenomena is not fully understood, but it has led to significant research into visual perception. In addition to providing ways to research human abilities, illusions like the lilac chaser intrigue and entertain people, reflecting our cognitive curiosity and endless appreciation for creativity that is part of human nature.

Discovery

The illusion was created by Jeremy Hinton some time before 2005. Hinton stumbled across the configuration while devising stimuli for visual motion experiments. In one version of a program to move a disk around a central point, he mistakenly omitted to erase the preceding disk, which created the appearance of a moving gap. Upon noticing the moving green-disk afterimage, he adjusted foreground and background colors, number of disks, and timing in order to optimize the effect. Later, Hinton blurred the disks, allowing them to disappear when a viewer looks steadily at the central cross. Hinton entered the illusion in the ECVP Visual Illusion Contest, but was disqualified for lack of registration. He then approached Michael Bach, who placed it on his web page of illusions^[1] and named it. The illusion quickly spread across the internet.

Description

Lilac chaser consists of a group of 12 lilac, blurred disks arranged around a small black cross. Each disk disappears briefly in clockwise order. When staring at the central cross, a viewer first sees a gap rotating around the circle, then a green disk that rotates around the circle, and finally, the disappearance of the lilac disks themselves.

Explanation

The lilac chaser illusion combines three simple, well-known effects:

The first effect (the moving gap) is due to the phi phenomenon. The moving gap creates a sense of apparent motion, similar to the way we perceive a series of still pictures as a moving image in film.

The moving gap becomes a rotating green disk because of afterimages. When the retina is stimulated with a certain color, the cones of the eye react to a loss of stimulus by activating the complimentary color of the stimulus. Adaptation of rods and cones begins immediately when they are stimulated, when afterimages also start to grow. We normally do not notice them because we move our eyes about three times a second. In lilac chaser, we keep our eyes still, so the afterimages grow and are revealed as the stimulus disappears.

The blurred lilac disks disappear because of a phenomena known as Troxler's fading. When a blurry stimulus is presented to a region of the visual field away from where we are fixating, and we keep our eyes still, that stimulus will disappear even though it is still physically present. This occurs because, although our eyes move slightly when we are fixating at a point, in peripheral vision these movements are not large enough to shift the lilac disks to new neurons of the visual system. Their afterimages essentially cancel out the original images, and all one sees of the lilac disks is gray, except for the gap where the green afterimage appears. In fact, it is not necessary to fixate on the cross for the effect; any stationary fixation will work.

These effects combine to yield the remarkable sight of a green spot running around in a circle on a gray background where only stationary, flashing lilac spots occur. Occasionally it may seem as though the green afterimage eats up the lilac disks, giving the illusion its alternative, Pac-Man name.

Applications

Lilac chaser achieved a sort of cult-status on the Internet. Like many other similar illusions, the study of the perceptual effects of the illusion can be useful to scientists in the study of how the brain perceives and interprets visual information.

Notes

↑ Michael Bach, Web Page of illusions, Michaelbach.com, 2008. Retrieved January 7, 2007.

References
ISBN links support NWE through referral fees

Blue, Ronald C. 2005. A visual yet non-optical subjective intonation. 13 (3), p. 299 - 300. Electroneurobiología, 2005. Retrieved December 21, 2007.

External links

All links retrieved October 25, 2022.

Hinton's “Lilac Chaser”
"Electroneurobiology article" – The ontological nature of the color afterimages has been analyzed in this article, "A visual yet non-optical subjective intonation," by Mariela Szirko.

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[1] Michael Bach, Web Page of illusions, Michaelbach.com, 2008. Retrieved January 7, 2007.

[1]

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-{{Claimed}}{{Started}}{{Contracted}}
+{{Images OK}}{{Submitted}}{{Approved}}{{Paid}}{{Copyedited}}
 [[Category:Politics and social sciences]]
 [[Category:Psychology]]
+[[Category:Illusion]]
+[[Image:Lilac-Chaser.gif|right|thumb|380px|Stare at the center cross for at least 30 seconds to experience the three phenomena of the illusion.]]
-[[Image:Lilac-Chaser.gif|right|thumb|400px|Stare at the center cross for at least 30 seconds to experience the three phenomena of the illusion.]]
+'''Lilac chaser''' is a [[visual illusion]], also known as the '''Pac-Man illusion''', that spread across the [[Internet]] in 2005. Lilac chaser is very similar to [[phi phenomenon]], and consists of 12 [[lilac (color)|lilac]] (or pink or magenta-like), blurred disks arranged in a circle (like the numbers on a [[clock]]), around a small, black, central cross on a gray background.
+{{toc}}
+The apparent movement of the lilac chaser and similar phi phenomena is not fully understood, but it has led to significant research into visual perception. In addition to providing ways to research human abilities, illusions like the lilac chaser intrigue and entertain people, reflecting our cognitive curiosity and endless appreciation for [[creativity]] that is part of human nature.
-'''Lilac chaser''' is a [[visual illusion]], also known as the '''[[Pac-Man]] illusion'''. It consists of 12 [[lilac (color)|lilac]] (or pink or magenta-like), blurred disks arranged in a circle (like the numbers on a [[clock]]), around a small, black, central cross on a grey background. One of the disks disappears briefly (for about 0.1 second), then the next (about 0.125 second later), and the next, and so on, in a clockwise direction. When one stares at the cross for about 20 seconds or so, one first sees a gap running around the circle of lilac disks, then a green disk running around the circle of lilac disks, then a green disk running around on the grey background, the lilac disks appearing to have disappeared or to have been erased by the green disk.
+==Discovery==
+The illusion was created by [[Jeremy Hinton]] some time before 2005. Hinton stumbled across the configuration while devising stimuli for visual motion experiments. In one version of a program to move a disk around a central point, he mistakenly omitted to erase the preceding disk, which created the appearance of a moving gap. Upon noticing the moving green-disk afterimage, he adjusted foreground and background colors, number of disks, and timing in order to optimize the effect. Later, Hinton blurred the disks, allowing them to disappear when a viewer looks steadily at the central cross. Hinton entered the illusion in the [[ECVP]] Visual Illusion Contest, but was disqualified for lack of registration. He then approached [[Michael Bach]], who placed it on his web page of illusions<ref>Michael Bach, [http://www.michaelbach.de/ot/col_lilacChaser/index.html Web Page of illusions], Michaelbach.com, 2008. Retrieved January 7, 2007.</ref> and named it. The illusion quickly spread across the internet.
-An interactive version of the illusion may be found [http://www.michaelbach.de/ot/col_lilacChaser/index.html here]. This version allows viewers to adjust the [[color]], [[saturation (color theory)|saturation]], and timing of the disks.
+==Description==
+Lilac chaser consists of a group of 12 lilac, blurred disks arranged around a small black cross. Each disk disappears briefly in clockwise order. When staring at the central cross, a viewer first sees a gap rotating around the circle, then a green disk that rotates around the circle, and finally, the disappearance of the lilac disks themselves.
-The illusion spread around the [[Internet]] in 2005 (see External Links).
-==History==
-The illusion was invented by [[Jeremy Hinton]] some time before 2005. He stumbled across the configuration while devising stimuli for visual motion experiments. In one version of a program to move a disk around a central point, he mistakenly omitted to erase the preceding disk, which created the appearance of a moving gap. On noticing the moving green-disk afterimage, he adjusted foreground and background colors, number of disks, and timing to optimize the effect.
-In 2005 Hinton blurred the disks, allowing them to disappear when a viewer looks steadily at the central cross. Hinton entered the illusion in the [[ECVP]] Visual Illusion Contest, but was disqualified for not being registered for that year's conference. He then approached [[Michael Bach]], who placed it on his [http://www.michaelbach.de/ot/col_lilacChaser/index.html web page of illusions] and named it. Then the illusion was duplicated on a web page for Mark Levinson's Design Services [http://www.patmedia.net/marklevinson/cool/cool_illusion.html]. Someone noticed this version and promoted it via e-mail or via an electronic bulletin board. Others did the same, spreading the illusion across the internet.
 ==Explanation==
 The lilac chaser illusion combines three simple, well-known effects:
-First, when a visual event occurs briefly at one place in the visual field, and then a similar event occurs at an adjacent place in the same visual field, we [[motion perception|perceive movement]] from the first place to the second. This is called [[apparent motion|apparent movement]] or [[beta movement]], because no actual movement has occurred.  Apparent movement is the basis of moving [[neon sign]]s, [[film]], and [[video]]. We see movement because such displays stimulate receptors (called [[Reichardt detector]]s) in our [[visual cortex|brain]]s that encode movement.The visual events in lilac chaser initially are the disappearances of the lilac disks. The visual events then become the appearances of green afterimages (see next).
+The first effect (the moving gap) is due to the [[phi phenomenon]]. The moving gap creates a sense of [[apparent motion]], similar to the way we perceive a series of still pictures as a moving image in [[film]].
-Second, when a lilac stimulus that is presented to a particular region of the visual field for a long time (say 10 seconds or so) disappears, a green [[afterimage]] will appear. The afterimage lasts only a short time, and in this case is effaced by the reappearance of the lilac stimulus. The afterimage is a simple consequence of [[adaptation]] of the [[Rod cell|rods]] and [[cone cell|cones]] of the [[retina]]. Color and brightness are encoded by the ratios of activities in three types of cones (and also the rods under [[mesopic]] conditions). The cones stimulated by lilac get "tired." When the stimulus disappears, the tiredness of some of the cones means that the ratios evoked by the grey background are the same as if a green stimulus had been presented to these cones when they are fresh. Adaptation of rods and cones begins immediately when they are stimulated, so afterimages also start to grow. We normally do not notice them because we [[Fixational eye movement|move our eyes]] about three times a second, so the image of a stimulus constantly falls on new, fresh, unadapted rods and cones. In lilac chaser, we keep our eyes still, so the afterimages grow and are revealed when the stimulus disappears.
-Third, when a blurry stimulus is presented to a region of the visual field away from where we are fixating, and we keep our eyes still, that stimulus will disappear even though it is still physically presented. This is called [[Troxler's fading]]. It occurs because although our eyes move a little when we are fixating a point, away from that point (in ''[[peripheral vision]]'') the movements are not large enough to shift the lilac disks to new neurons of the visual system. Their afterimages essentially cancel the original images, so that all one sees of the lilac disks is grey, except for the gap where the green afterimage appears.
-These effects combine to yield the remarkable sight of a green spot running around in a circle on a grey background when only stationary, flashing lilac spots have been presented. Occasionally it seems as though the green afterimage has eaten up the lilac disks, this resemblence to Pac-Man accounting for the illusion's alternative name.
-==Psychophysics==
-By December 2005, no systematic study of the stimulus properties of the illusion had been published. Hinton optimized the conditions for all three aspects of the illusion before releasing it. He also noted that the color of the green disk could be outside the color gamut of the monitor on which it was created. Michael Bach's version of the illusion allows viewers to adjust some aspects of the illusion. It is simple to confirm that the illusion occurs with other colors, and that Troxler fading is enhanced by reducing the saturation of the disks.
-==Other effects==
-The demonstration in this article shows a blurred, very slightly blue-grey disk in each gap. These can be seen by examining one frame of the image under high magnification with any adjoining lilac disks masked off. But these blurred disks are not required for the illusion. The demonstration at [http://www.michaelbach.de/ot/col_lilacChaser/index.html web page of illusions] contains no such disks, but yields the illusion.
+The moving gap becomes a rotating green disk because of [[afterimage]]s. When the [[retina]] is stimulated with a certain color, the [[cone cell|cones]] of the eye react to a loss of stimulus by activating the [[complimentary]] color of the stimulus. Adaptation of rods and cones begins immediately when they are stimulated, when afterimages also start to grow. We normally do not notice them because we [[Fixational eye movement|move our eyes]] about three times a second. In lilac chaser, we keep our eyes still, so the afterimages grow and are revealed as the stimulus disappears.
-It is not necessary to fixate the black cross for the effects to occur. As long as the eyes are held steadily on any point of the figure (e.g., the center of the three o'clock disk), they will occur.
+The blurred lilac disks disappear because of a phenomena known as [[Troxler's fading]]. When a blurry stimulus is presented to a region of the visual field away from where we are fixating, and we keep our eyes still, that stimulus will disappear even though it is still physically present. This occurs because, although our eyes move slightly when we are fixating at a point, in [[peripheral vision]] these movements are not large enough to shift the lilac disks to new neurons of the visual system. Their afterimages essentially cancel out the original images, and all one sees of the lilac disks is gray, except for the gap where the green afterimage appears. In fact, it is not necessary to fixate on the cross for the effect; any stationary fixation will work.
-If instead of fixating the black cross, one follows the moving gap with one's eyes, one will see only a moving gap and 12 lilac disks rather than a single green disk. This is because the green disk arises as an afterimage, requiring the eyes to be held steadily to occur, and the disappearance of the lilac disks is from Troxler's fading, also requiring the eyes to be held steadily to occur. Moving the eyes prevents the formation of afterimages and the occurrence of Troxler's fading.
+These effects combine to yield the remarkable sight of a green spot running around in a circle on a gray background where only stationary, flashing lilac spots occur. Occasionally it may seem as though the green afterimage eats up the lilac disks, giving the illusion its alternative, [[Pac-Man]] name.
-If after looking at the effect for 30 seconds or so, one moves one's eyes elsewhere (e.g., to another point on the figure or to a blank sheet of white paper), one will see a stationary ring of 12 green disks that will fade after a short time. These green disks are the afterimages of the 12 lilac disks.
+==Applications==
+Lilac chaser achieved a sort of cult-status on the [[Internet]]. Like many other similar illusions, the study of the perceptual effects of the illusion can be useful to scientists in the study of how the brain perceives and interprets visual information.
-If one watches the illusion for long enough to see only the green disk and then moves away from the computer screen while keeping the eyes on the cross, one sees larger green spots outside a ring of lilac spots with a smaller green disk running around them. The smaller green disk may merge briefly with the outer green spots, making the spots appear to be radial blobs. The outer green spots soon fade. These outer green spots are afterimages that appear larger because of [[Emmert's Law]]: the size of an afterimage becomes larger as its viewing distance is increased. They are outside because moving away from the computer screen has decreased the [[visual angle]] of the lilac spots. They fade because the lilac disks that constantly refresh the green afterimages are now projected onto a different part of the retina. If one moves towards the screen, the effects are opposite.
+==Notes==
+<references/>
+==References==
+* Blue, Ronald C. 2005. [http://electroneubio.secyt.gov.ar/non-optic_visual_intonation.htm A visual yet non-optical subjective intonation]. 13 (3), p. 299 - 300. Electroneurobiología, 2005. Retrieved December 21, 2007.
 ==External links==
+All links retrieved October 25, 2022.
+*[http://www.michaelbach.de/ot/col-lilacChaser/index.html Hinton's “Lilac Chaser”]
+*[http://electroneubio.secyt.gov.ar/non-optic_visual_intonation.htm "Electroneurobiology article"] – The ontological nature of the color afterimages has been analyzed in this article, "A visual yet non-optical subjective intonation," by Mariela Szirko.
-*http://www.planetperplex.com/en/jeremy_hinton.html
-*http://www.fusionlangaming.com/forum/showthread.php?t=7379
-*http://www.bsangha.net/articles/lilac_chaser.html Jeremy Hinton's explanation
-*http://www.seanbuckley.ca/blog/2005/09/03/purple-dots-mind-trick/
-*http://xona.com/opticalillusions/
-*http://weblog.frittle.org/article/29/optical-illusions-and-visual-phenomena
-*http://www.stumbleupon.com/url/www.michaelbach.de/ot/col_lilacChaser/index.html
-*[http://www.michaelbach.de/ot/col_lilacChaser/index.html "Michael Bach's explanation]
-*[http://electroneubio.secyt.gov.ar/non-optic_visual_intonation.htm "Electroneurobiology article"]. The [[ontological]] nature of the color afterimages have been analyzed in this article, "A visual yet non-optical subjective intonation," by Mariela Szirko.
 {{Credits|Lilac_chaser|156710438|}}