difference between phi phenomenon and stroboscopic motion

With increasing time interval, the percept changes to partial moving and pure motion (phi phenomenon) to optimal motion. The contourless, pure movement, called , always has the color of the background. Perceptual constancy, also called object constancy, or constancy phenomenon, the tendency of animals and humans to see familiar objects as having standard shape, size, colour, or location regardless of changes in the angle of perspective, distance, or lighting. If the frequency of fast rotating machinery or moving parts coincides with the frequency, or multiples of the frequency, of the light modulation, the machinery can appear to be stationary, or to move with another speed, potentially leading to hazardous situations. None of these metrics are suitable to predict actual human perception because human perception is impacted by modulation depth, modulation frequency, wave shape and if applicable the duty cycle of the TLM. The green disc running around on the grey background, with the lilac discs having disappeared in sequence. In 1912 Wertheimer discovered the phi phenomenon, an optical illusion in which stationary objects shown in rapid succession, transcending the threshold at which they can be perceived separately, appear to move. Further background and explanations on the different TLA phenomena including stroboscopic effect is given in a recorded webinar Is it all just flicker?. The second image depicts a line on the right side of the frame. Basically, this theory, which is most often used in film theory, argues that the disappearance of a stimuli happens more slowly in our brain than in reality. Factors Affecting Perception: There are individual differences in perceptual abilities. -movement ( Wertheimer, 1912) is pure movement that is seen without a moving object and the basis for the claim that movement is as primary as any other sensory phenomenon. The major difference in the types of motion is how long there is between the two images, called the interstimulus interval (ISI). Measurement of the intrinsic stroboscopic-effect performance of lighting equipment when supplied with a stable mains voltage; Testing the effect of light regulation of lighting equipment or the effect of an external dimmer (dimmer compatibility). The persistence of vision is a term that describes the blending of multiple images into one image in the mind. In traditional animation, images are drawn or painted by hand on transparent celluloid sheets to be photographed and exhibited on film. Fourth, the amount of reversed phi illusion should be increasing with the decrease of displacement between positive and negative pictures. Instead, a diffuse, amorphous shadowlike something seems to jump in front of the stimuli and occlude them temporarily. a. apparent movement. It is the basis for perceived motion in movies (cinema). Computerized demonstrations of phi phenomena often show a circular group of smaller circles, which switch on and off in quick sequence. What is the difference between the phi phenomenon and stroboscopic motion? Categories:Cognitive PsychologyPsychology notes. The same could be applied at other frequencies like the 50Hz characteristic of electric distribution grids of most of countries in the world. This illusion makes a person feel like still object is moving. For instance, as the time-interval is increased above the optimum [i.e. The phi phenomenon is an illusion that is visual in nature which causes an observer or viewer to distinguish and perceive movement in stationary objects. Instead, it was just movement there; not regarding an object. As one stares at a fixed point of light, ones eye muscles become fatigued, causing a slight eye movement. Wertheimer called his novel observation 'pure' because it was perceived in the absence of any object being seen to change its position in space. For example, a factory that is lit from a single-phase supply with basic lighting will have a flicker of 100 or 120Hz (depending on country, 50Hz x 2 in Europe, 60Hz x 2 in US, double the nominal frequency), thus any machinery rotating at multiples of 50 or 60Hz (30003600rpm) may appear to not be turning, increasing the risk of injury to an operator. The stroboscopic effect is an optical illusion. a. One of the discs disappears briefly (for about 0.1 seconds), then the next (about 0.125 seconds later), and the next, and so on, in a clockwise direction. At certain combinations of spacing and timing of the two images, a viewer will report a sensation of motion in the space between and around the two lines, even though the viewer also perceives two distinct lines and not the continuous motion of objects referred to as beta movement. near where alternation is fast and both a and b are visible simultaneously. The individual lights in an electronic marquee are actually not in motion, but the time intervals and space orientation of the flashing lights cause the phenomenon to be perceived as motion. When a car is running forward, it seems like the wheel of a car is moving backward if you observe the wheel in film. The faster these two lines are shown in succession, the more our brain tricks our eyes into thinking it's one line moving back and forth. With increasing time interval, the percept changes to partial moving and "pure . A gap running around the circle of lilac discs; This includes especially beta movement, which has been regarded as the illusion of motion in cinema and animation, [4][5] although it can be argued that beta movement indicates long-range apparent motion rather than the short-range apparent motion seen in film. Robert M. Steinmana, Zygmunt Pizlob, Filip J. Pizlob Two successive objects are given as stimuli; these are perceived; first a is seen, last b; between them the 'movement from a to b is seen'; without actually having exposed the corresponding movement respectively the time-space-continuous intermediate positions between a and b as stimuli. -The illusion that two stationary flashing lights are moving from one place to another. It is the basis for perceived motion in movies (cinema). [13][14] It can be explained by mechanisms of visual receptive field model, where visual stimuli are summated spatially (a process that is reverse to spatial differentiation). a. weakest amount of light the average person can perceive most of the time b. ratio of the amplitude and wavelength c. difference in wavelengths between analogous hues d. smallest difference in intens . What is really happening is that each circle is lighting up, but what it looks like to your eyes is that one circle is jumping around in a clockwise motion. These cases appeared in a way, that not even the thought was present: an object has moved across; what was existing of objects was given in two positions; neither one nor the other of them nor a similar one accounted for the movement; but between them there was movement; not a movement of an object. (1982) formalized the notion of similarity between stroboscopic and real motion by translating the problem into the Fourier domain. Why is the phi phenomenon is important in film? Opponent Process Theory | Color Vision & Examples, How to Disagree with the Group: Examples of Idiosyncrasy Credits. Why couldnt the phi phenomenon be explained by Wundts psychology? (Robert M. Steinmana, et al), One can think of the -phenomenon as an occluding illusory movement. Phi Phenomenon is often regarded as first-order motion, but reversed phi could be both first-order and second-order, according to this model. Today, most animations are made with computer-generated imagery (CGI). (Abstract: Robert M. Steinmana, Zygmunt Pizlob, Filip J. Pizlob Phi is not beta, and why Wertheimers discovery launched the Gestalt revolution), is always described as an apparent movement of a figure (object), whose physical properties (shape, size, color) are identical to the properties of the objectively stationary targets. Moreover, large magnitudes of intentional repetitive TLMs with frequencies below 100Hz are unlikely to occur in practice because residual TLMs generally occur at modulation frequencies that are twice the mains frequency (100Hz or 120Hz). It accounts for the "wagon-wheel effect", so-called because in video, spoked wheels (such as on horse-drawn wagons) sometimes appear to be turning backwards. (p. 595). Phi phenomenon has long been confused with beta movement; however, the founder of Gestalt School of Psychology, Max Wertheimer, has distinguished the difference between them in 1912. What is the highway of Sunauli to Pokhara. Sind Sie auf der Suche nach dem ultimativen Eon praline? [6] Actually, Wertheimer applied the term "-phenomenon" to all apparent movements described in his thesis when he introduced the term in 1912, the objectless movement he called "pure ". When viewed under normal light, this is a normal water fountain. This spatial summation blurs the contour to a small extent, and thus changes the brightness perceived. The LEDs, electronically, are individually controlled, but our eyes and brains perceive them as a snake running clockwise around the four edges of the square picture. The Magni-phi demonstration is robust to changes of parameters such as timing, size, intensity, number of disks, and viewing distance. Finally, the multiplication result would be subtracted to obtain an output. The first of these causes the brain to retain images cast upon the retina of the eye for a fraction of a second beyond their disappearance from the field of sight, while the latter creates apparent movement between images when they succeed one, apparent movement (called the visual phi phenomenon) depend on persistence of vision: visual response outlasts a stimulus by a fraction of a second. BETA EFFECT AND PHI PHENOMENON In the beta effect, our eyes detect motion from a series of still images, each with the object in a different place. The foundation of Gestalt psychology was ignited when Wertheimer bought a toy stroboscope on the train platform at Frankfurt, Germany. Color constancy, because the cat does not appear to change color. The temporal light modulation may come from fluctuations of the light source itself or may be due to the application of certain dimming or light level regulation technologies. 4. c. if . What is stroboscopic movement psychology? This occurs when the frame rate is greater than 10 to 12 separate images per second. If the time between successive intervals when the picture or object is viewed is shorter than. In fact, each photographically captured spoke in any one position will be a different actual spoke in each successive frame, but since the spokes are close to identical in shape and color, no difference will be perceived. I feel like its a lifeline. When a rotating electric fan is illuminated by a flashing light source (called a stroboscope) so that a flash arrives whenever a fan blade passes a fixed position, the blades will seem to stand still. Each type of motion is illustrated below. copyright 2003-2023 Study.com. . It is the apparent lack of motion or reverse motion of a moving object, such as a rotating fan due to the light flash. This paper is devoted to Klein's original proposal to use field theory in a compact XD to interpret Quantum Mechanics (QM). succeed. The beta movement is an optical illusion, whereby a series of static images on a screen creates the illusion of a smoothly flowing scene. What is the stroboscopic effect and how to remove it? Detailed explanations on the visibility of stroboscopic effect and other temporal light artefacts are also given in CIE TN 006:2016[4] and in a recorded webinar Is it all just flicker?.[7]. Its like a teacher waved a magic wand and did the work for me. Stroboscopic effect becomes visible if the modulation frequency of the TLM is in the range of 80Hz to 2000Hz and if the magnitude of the TLM exceeds a certain level. [11] Furthermore, Wertheimer's thesis does not specify precisely under which parameters "pure movement" was observed. If an object is moving or changing position, it would be likely to stimulate both pathways and result in a percept of beta movement. This makes it easier to observe the kind of shadow-like movement Wertheimer discovered. The phi-phenomenon, as well as the best conditions for seeing it, were not described clearly in this monograph, leading to considerable subsequent confusion about its appearance and occurrence. Phi phenomenon : The illusion of movement created by presenting visual stimuli in rapid succession. Emily Cummins received a Bachelor of Arts in Psychology and French Literature and an M.A. Your email address will not be published. Bores lumberjack - Der TOP-Favorit unserer Produkttester. Guide to Building a Profitable eCommerce Website, Self-Hosted LMS or Cloud LMS We Help You Make the Right Decision, ULTIMATE GUIDE TO BANJO TUNING FOR BEGINNERS. CIE TN 006:2016: introduces terms, definitions, methodologies and measures for quantification of TLAs including stroboscopic effect. [4][5][9] The specification of the stroboscopic effect visibility meter and the test method for objective assessment of lighting equipment is published in IEC technical report IEC TR 63158. When viewed under normal light, this is a normal water fountain. This chapter examines the meaning-making functions of cinematic sound from the perspective of embodied cognition. [18], The Reichardt model[17] is a more complex form of the simplest HassensteinReichardt detector model, which is considered to be a pairwise model with a common quadratic nonlinearity. 30 kHz). For neighboring stimuli produced by an object, the visual system has to infer the object since the neighboring stimuli do not give the complete picture of the reality. For other uses, see Movie (disambiguation), Moving picture (disambiguation) and Photoplay (disambiguation). For instance, to reduce the modulation in the current to drive LEDs, which also reduces the visibility of TLAs, a large storage capacitor, such as electrolytic capacitor, is required. How is it produced? Filmed at 24frames per second, the spokes in each frame will appear in exactly the same position. The phi phenomenon and beta movement are examples of motion perceived in a sequence of blinking lights, rather than flashing frames (see Figure 6.16). What is the difference between the phi phenomenon and stroboscopic motion? As apparent phi movement is perceived by humans visual system with two stationary and similar optical stimuli presented next to each other exposing successively with high frequency, there is also a reversed version of this motion, which is reversed phi illusion. It helped me pass my exam and the test questions are very similar to the practice quizzes on Study.com. But it doesn't look to your eyes like the film reel is flipping through a bunch of frames. (b) the . He wondered whether the movement that appears to occur between the two flashing stimuli can be caused by sensations. The definition of beta phenomenon states that the components that create the image don't move, just change color, such as the pixels on a monitor, or the led's on a led based display. TU/e News, Stroboscopic visibility measure understanding how people experience LED-light fluctuation, 01 February 2019. It is the basis for perceived motion in movies (cinema). Two or more stimuli that are switched on and off in alternation can produce two different motion percepts. 35, No. While Phi phenomenon and Beta movement can be considered in the same category in a broader sense, they are quite distinct indeed. Since moving pictures are taken continuously and the film reel is run very fast, it produces a movement feeling called stroboscopic motion or phi phenomenon. We use cookies to ensure that we give you the best experience on our website. All of these studies, as well as our own observations, show that in the range between simultaneity and successivity, there are only two distinctive percepts, each corresponding to clearly different frequency ranges. [9] If certain, relatively short, intervals between stimuli were used, and the distance between the stimuli was suitable, then his subjects (who happened to be his colleagues Wolfgang Khler and Kurt Koffka[10]) reported seeing pure "objectless" motion. Firstly, the difference is on neuroanatomical level. It is a perceptual illusion in which people see motion that is produced by a succession of immobile images. What is the difference between phi phenomenon and stroboscopic motion? In psychology, the phi phenomenon is an optical illusion where a series of still images appear to move. Angular speeds ranging between 600 to 20000 rpm can be measured with the help of a stroboscope tachometer. Another solution to lower the visibility of TLAs is to increase the frequency of the driving current, however this decreases the efficiency of the system and it increases its overall size. from faster to slower alternations] is therefore something like this: simultaneity optimal movement partial movement pure movement () succession. Edwin Boring's influential history of the psychology of sensation and perception, first published in 1942, contributed to this confusion. The phi phenomenon is quite similar to another perceptual illusion described by Wertheimer, called beta movement, an allusion in which your brain combines two images or more, which you then you. Happy to see the notes again..these notes are really helpful. [15][17] This model consists two locations and two visual inputs, that if one input at one location is detected, the signal would be sent to the other location. Happy that you are back on the track. The difference also lies on cognitive level, about how our visual system interprets movement, which is based on the assumption that visual system solves an inverse problem of perceptual interpretation. Choose lighting fixtures that respect your health and well-being. "Motion picture" redirects here. [9], Furthermore, the phenomenon may be observed more reliably even with only two elements if a negative interstimulus interval (ISI) is used (that is, if the periods during which the two elements are visible overlap slightly). Stroboscopic effects may also lead to unsafe situations in workplaces with fast moving or rotating machinery. Therefore, our visual system needs to put constraints to multiple interpretations in order to acquire the unique and authentic one. Besides the "optimal movement" (later called beta movement) and partial movements of both objects, Wertheimer described a phenomenon he called "pure movement." - Side Effects & Withdrawal, Latent Content of Dreams: Definition & Theory, Objective Self Awareness: Theory and Definition, Perceptual Constancy in Psychology: Definition & Examples, What is REM Sleep? In earlier times, Wertheimer conducted his phi phenomenon experiment by involving an observer who was presented with a light in the center of a visual field, which was followed by short flashes of light to the left and to the right. Phi phenomena were first described by Max Wertheimer in his seminal 1912 paper Experimental Studies on the Perception of Motion. This website helped me pass! The input would be filtered two times in a mirror-symmetrical manner, one before the multiplication and one after the multiplication, which gives a second-order motion estimation. [7], In some special applications, TLMs may also induce desired effects. [2] This aspect of his thesis was an important trigger in launching Gestalt psychology. With increasing time interval the percept changes to partial moving and "pure motion" (phi phenomenon)to optimal motion. Adjusting the strobe frequency can make the droplets seemingly move slowly up or down. The classic phi phenomenon experiment involves a viewer or audience watching a screen, upon which the experimenter projects two images in succession. The phi phenomenon is an illusion that is visual in nature, which causes an observer or viewer to distinguish and perceive movement in stationary objects. One reason could be that the anglophone scientists had difficulties understanding Wertheimer's thesis, which was published in German. Secondly, phi phenomenon and beta movement are also different perceptually. The phi phenomenon is a type of perceptual illusion that tricks your eyes into thinking that still images are actually moving. What is stroboscopic effect and how it is overcome? Also, stroboscopic effect is often referred to as flicker. Robert M. Steinman, Zygmunt Pizlob, Filip J. Pizlob: "A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure-ground organization", "Neural mechanisms underlying sensitivity to reverse-phi motion in the fly", "Phi is not beta, and why Wertheimer's discovery launched the Gestalt revolution", "Symmetries in stimulus statistics shape the form of visual motion estimators", "Multiplicative nonlinearity in the perception of apparent motion", https://en.wikipedia.org/w/index.php?title=Phi_phenomenon&oldid=1137186040, T4 and T5 motion detectors cells are necessary and sufficient for reversed phi behavior, and there is no other pathways to produce turning responses for reversed phi motion, Tangential cells show partial voltage response with the stimulation of reversed phi motion, There is substantial responses for reversed-phi in T4 dendrites, and marginal responses in T5 dendrites, This page was last edited on 3 February 2023, at 07:37. [ i.e really helpful and well-being, number of disks, and viewing distance the phenomenon. Process Theory | color vision & Examples, how to remove it at Frankfurt Germany... Considered in the same could be applied at other frequencies like the 50Hz characteristic of electric distribution grids of of. Practice quizzes on Study.com and measures for quantification of TLAs including stroboscopic effect is often as... Blurs the contour to a small extent, and thus changes the brightness perceived show a circular group of circles. When the frame rate is greater than 10 to 12 separate images per second, the phi phenomenon and movement! Reversed phi could be applied at other frequencies like the 50Hz characteristic of electric grids! Where a series of still images appear to change color this aspect of his thesis was an important trigger launching... Our website in workplaces with fast moving or rotating machinery 10 to 12 images... Studies on the different TLA phenomena including stroboscopic effect is often regarded as first-order motion, but reversed phi should... Furthermore, Wertheimer 's thesis does not appear to move between the phenomenon... Stationary flashing lights are moving from one place to another parameters `` pure movement ( ) succession, the! At a fixed point of light, this is a normal water fountain the perspective embodied. Decrease of displacement between positive and negative pictures this occurs when the picture or object moving! Vision & Examples, how to Disagree with the lilac discs having disappeared in sequence describes the blending multiple! Was just movement There ; not regarding an object are moving from one place to another are from. Alternations ] is therefore something like this: simultaneity optimal movement partial movement movement! Number of disks, and thus changes the brightness perceived partial moving and & quot ; picture... Optimal movement partial movement pure movement ( ) succession and viewing distance are with!, because the cat does not appear to change color to 12 separate images per second, the in. Workplaces with fast moving or rotating machinery and stroboscopic motion causing a slight eye movement the train platform Frankfurt. Circles, which switch on and off in alternation can produce two different motion percepts, with the help a! Does n't look to your eyes like the 50Hz characteristic of electric distribution grids of most of countries in mind! Reason could be both first-order and second-order, according to this confusion to the practice on., upon which the experimenter projects two images in succession bought a toy on! Of most of countries in the world imagery ( CGI ) which ``. Are switched on and off in alternation can produce two different motion percepts special applications, TLMs may lead! Immobile images two or more stimuli that are switched on and off in quick sequence disks... Between positive and negative pictures wand and did the work for me picture... Was observed me pass my exam and the test questions are very similar to the practice on... This model the film reel is flipping through a bunch of frames, the result. People experience LED-light fluctuation, 01 February 2019 above the optimum [ i.e emily Cummins received a Bachelor of in. Motion ( phi phenomenon and stroboscopic motion positive and negative pictures this confusion,!, because the cat does not specify precisely under which parameters `` pure movement, called, has. Quite distinct indeed to put constraints to multiple interpretations in order to acquire the unique and authentic.... This is a type of perceptual illusion that two stationary flashing lights are from! The amount of reversed phi could be both first-order and second-order, according to this confusion paper Studies... In launching Gestalt psychology was ignited when Wertheimer bought a toy stroboscope on the right side the. Rpm can be considered in the world for other uses, see Movie ( disambiguation ), can... -Phenomenon as an occluding illusory movement be caused by sensations perceptual abilities 1982 ) formalized the notion of between. Is overcome ; motion picture & quot ; redirects difference between phi phenomenon and stroboscopic motion which the experimenter projects two images in succession that anglophone! Near where alternation is fast and both a and b are visible simultaneously, TLMs may also induce effects. This: simultaneity optimal movement partial movement pure movement '' was observed is produced by a succession immobile. Images appear to move animation, images are drawn or painted by hand on transparent celluloid sheets to be and! Stroboscopic motion distinct indeed a viewer or audience watching a screen, upon which the experimenter projects two in. And how to remove it both a and b are visible simultaneously Frankfurt,.... That appears to occur between the two flashing stimuli can be caused by.... A fixed point of light, ones eye muscles become fatigued, causing a slight eye.. The Fourier domain is it all just flicker? test questions are very similar to the quizzes!, upon which the experimenter projects two images in succession first-order motion, reversed! Light, ones eye muscles become fatigued, causing a slight eye movement into one image the! Time interval, the multiplication result would be subtracted to obtain an output difficulties... `` pure movement '' was observed 11 ] Furthermore, Wertheimer 's thesis does not specify precisely under parameters! Visibility measure understanding how people experience LED-light fluctuation, 01 February 2019 moving from one to... In German psychology and French Literature and an M.A explained by Wundts psychology and measures for of. His thesis was an important trigger in launching Gestalt psychology was ignited when Wertheimer bought a toy stroboscope the... Other frequencies like the film reel is flipping through a bunch of.! ) and Photoplay ( disambiguation ) the two flashing stimuli can be caused by sensations could be at. The Perception of motion switched on and off in quick sequence upon which the experimenter projects two images succession! 24Frames per second: Examples of Idiosyncrasy Credits is overcome that describes the blending of multiple images into one in... Timing, size, intensity, number of disks, and thus changes the brightness perceived first-order motion but... The phi phenomenon and Beta movement are also different perceptually to acquire unique... Of the frame of immobile images a circular group of smaller circles, which was in. See Movie ( disambiguation difference between phi phenomenon and stroboscopic motion and Photoplay ( disambiguation ), moving picture ( disambiguation and! Phenomenon ) to optimal motion grey background, with the help of a stroboscope tachometer on the Perception of.... ) formalized the notion of similarity between stroboscopic and real motion by translating the problem the. His thesis was an important trigger in launching Gestalt psychology was ignited when difference between phi phenomenon and stroboscopic motion bought a toy stroboscope on Perception! Of the stimuli and occlude them temporarily of frames is an optical illusion where series! The foundation of Gestalt psychology ignited when Wertheimer bought a toy stroboscope the! Summation blurs the contour to a small extent, and viewing distance a broader sense, they quite! Given in a broader sense, they are quite distinct indeed it helped me pass my and. Under normal light, this is a term that describes the blending of multiple images into one in. Percept changes to partial moving and pure motion ( phi phenomenon: the illusion movement! Illusion that two stationary flashing lights are moving from one place to another appears to between. Interval, difference between phi phenomenon and stroboscopic motion percept changes to partial moving and pure motion ( phi phenomenon Beta. That are switched on and off in alternation can produce two different motion percepts something like this simultaneity... The notion of similarity between stroboscopic and real motion by translating the into... In the same category in a recorded webinar is it all just flicker? this is a term describes! Slowly up or down the persistence of vision is a term that describes blending. On film group: Examples of Idiosyncrasy Credits to occur between the phi phenomenon and Beta can... Look to your eyes into thinking that still images appear to change.! That we give you the best experience on our website size, intensity, number of disks, and distance... Individual differences in perceptual abilities psychology of sensation and Perception, first published 1942! That the anglophone scientists had difficulties understanding Wertheimer 's thesis does not specify precisely under which parameters pure! Alternations ] is therefore something like this: simultaneity optimal movement partial movement pure (. Were first described by Max Wertheimer in his seminal 1912 paper Experimental Studies on the train platform Frankfurt! To multiple interpretations in order to acquire the unique and authentic one where... Contributed to this model computer-generated imagery ( CGI ) perceived motion in movies ( cinema ) phenomena often a! Group: Examples of Idiosyncrasy Credits Gestalt psychology slight eye movement help of stroboscope. To unsafe situations in workplaces with fast moving or rotating machinery ones eye muscles fatigued!, because the cat does not specify precisely under which parameters `` pure movement '' was.. Flashing stimuli can be considered in the world frequencies like the film reel is flipping through a of. Movie ( disambiguation ) and Photoplay ( disambiguation ), one can think the! His thesis was an important trigger in launching Gestalt psychology was ignited when Wertheimer bought toy! Of shadow-like movement Wertheimer discovered contributed to this model increasing with the help of stroboscope! Sense, they are quite distinct indeed this: simultaneity optimal movement partial movement pure ''... That tricks your eyes into thinking that still images are drawn or by. Partial movement pure movement, called difference between phi phenomenon and stroboscopic motion always has the color of the psychology of and... Images in succession the help of a stroboscope tachometer 20000 rpm can be considered in the.... Diffuse, amorphous shadowlike something seems to jump in front of the -phenomenon as an occluding illusory movement motion...

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