Wagon-wheel effect

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The wheelbar effect (alternatively, stagecoach-wheel effect , stroboscopic effect ) is an optical illusion in which the wheels are spun differently from rotation original. Wheels can rotate more slowly than actual rotation, the wheels can be seen still, or can rotate in the opposite direction from the actual rotation. The last form of this effect is sometimes called reverse rotational effect .

Wheelwagon effects are most often seen in films or television shows of stagecoaches or carts in Western movies, although recordings of every rotating rotating object will show it regularly, such as helicopter rotors and aircraft propellers. In this media recording, the effect is the result of a temporary aliation. This is also often seen when the spinning wheel is illuminated by blinking light. These forms of effect are known as stroboscopic effects: the original fine rotation of the wheel can only be seen intermittently. Versions of the wagon wheel effect can also be seen under continuous illumination.

Video Wagon-wheel effect

In stroboscopic condition

The stroboscopic conditions ensure that the visibility of the spinning wheel is broken down into a series of short episodes in which the motion is absent (in the case of film cameras) or minimal (in the case of stroboscopes), disturbed by longer transparent episodes. It is customary to call the previous episode frame . An analog film camera that records images on film typically operates at 24 frames per second while digital film cameras operate at 25 frames per second (PAL; European Standard), or at 29.97 frames per second (NTSC; Standards North America). Standard television operates at 59.94 or 50 images per second (the video frame is two separate images; see intertwine). Stroboscope can usually set the frequency to any value. Temporary lights are modulated temporarily when powered by alternating current, such as gas discharge lamps (including fluorescent, mercury vapor, sodium vapor and fluorescent tubes), flicker at twice the frequency of the power line (eg 100 times per second on 50 lines cycle). In each cycle of current, power peaks twice (once with positive voltage and once with negative voltage) and twice becomes zero, and light output varies accordingly. In all these cases, a person sees the wheel spinning under a stroboscopic condition.

Imagine that the true rotation of the four-finger wheel is clockwise. The first example of wheel visibility can occur when someone speaks at 12 o'clock. If at the next visibility sample occurs, the previous conversation at 9 o'clock has moved to 12 o'clock position, then the viewer will see the wheels become silent. If in the second instance of visibility, the next talk has moved to position 11:30, then the viewer will see the wheel spin backwards. If at second visibility, the next talk has moved to 12:30, then the viewer will see the wheel spin forward, albeit slower than the spinning wheel. The effect depends on the motion perception property called beta movement: the visible motion between two objects in different positions in the visual plane at different times provides the same object (the true of the talking wheel - each speaks essentially identical to the other) and provides near objects (which is actually from 9 am talking in second second - it's closer to 12 hours than the original 12-hour clock talk).

The wagon wheel effect is exploited in some engineering tasks, such as adjusting engine time. This same effect can make some spinning engines, like a lathe, dangerous to operate under artificial lighting because at certain speeds the fake machines will seem to stop or move slowly.

Finlay, Dodwell and Caelli (1984) and Finlay and Dodwell (1987) studied the perception of the wheel spinning under stroboscopic illumination when the duration of each frame was long enough for the observer to see the real rotation. Nevertheless, the direction of rotation is dominated by the wagon wheel effect. Finlay and Dodwell (1987) argue that there are some important differences between wagon wheel effects and beta motion, but their arguments do not interfere with consensus.

Maps Wagon-wheel effect

Under continuous illumination

Effective stroboscopic presentation with thrilling eyes

Rushton (1967) observed the effect of a wheelbarrow under continuous illumination while humming. The hum of the eye vibrates in its socket, effectively creating a stroboscopic condition inside the eye. By humming at the frequency of multiple rotation frequencies, it is able to stop the rotation. By humming at slightly higher and lower frequencies, it is able to slowly rotate backwards and make the rotation move slowly toward rotation. The same stroboscopic effect is now commonly observed by people who eat crunchy foods, such as carrots, while watching TV: the images look sparkling. The rattling thrill at the TV frame rate multiples. In addition to eye vibration, the effect can be generated by observing the wheels through a vibrating mirror. The rearview mirror in the vibrating car can produce an effect.

Really sustainable lighting

The first to observe the effect of wheelbarrow under continuous illumination (as from the sun) is Schouten (1967). He distinguished three forms of subjective stroboscopy which he called alpha, beta, and gamma: Alpha stroboscopy occurs at 8-12 cycles per second; the wheels seem to be stationary, although "some sectors [spokespersons] look as though they are doing an obstacle race on top of that stand" (p.Ãƒ, 48). Beta stroboscopy occurs in 30-35 cycles per second: "The difference in pattern has disappeared, sometimes there is a certain counterrotation of the gray-striped pattern" (pp.a, 48-49). Gamma stroboscopy occurs at 40-100 cycles per second: "The disk looks almost uniform except that at all sector frequencies gray standing pattern is visible... in a sort of quiescent" (pp. 49-50). Schouten interprets beta stroboscopy, inverse rotation, consistent with the Reichardt detector in the human visual system for motion coding. Because the wheel pattern that he uses (radial gratings) is regular, they can greatly stimulate the detector for actual rotation, but also weakly stimulate the detector for reverse rotation.

There are two broad theories for the effect of wheel carts under continuous illumination. The first is that the human visual perception takes a series of silent frames from the visual landscape and the movement is felt like a movie. The second is Schouten's theory: that moving images are processed by visual detectors that are sensitive to actual motion and also by detectors sensitive to opposite motions from temporary aliations. There is evidence for both theories, but the weight of evidence supports the latter.

Discrete framework

Purves, Paydarfar, and Andrews (1996) proposed discrete-frame theory. One proof for this theory comes from Dubois and VanRullen (2011). They review the experience of LSD users who often report that under the influence of drugs, moving objects are seen following a series of still images behind them. They asked the user to match their drug experience with a movie that simulates the trailing image as seen when not under the drug. They found that users chose movies about 15-20 Hz. This is between the alpha and beta levels of Schouten.

Temporary aliasing theory

Kline, Holcombe, and Eagleman (2004) confirm the observation of reversed rotation with regular dots on the rotating drum. They call this "reversal of the illusionary movement". They show that this happens only after a long view of the rotating screen (from about 30 seconds to 10 minutes for some observers). They also show that the incidence of rotation is inversely independent in different parts of the visual field. This is inconsistent with the discrete frame that covers the entire visual scene. Kline, Holcombe, and Eagleman (2006) also show that the reversed rotation of the radial lattice in one part of the visual field does not depend on superimposed orthogonal motions in the same part of the visual plane. The orthogonal movement is a circular lattice contraction and thus has the same temporal frequency as the radial lattice. This is inconsistent with discrete frames that include local parts of the visual scene. Kline et al. concluded that the inverse rotation consistent with the Reichardt detector for the reverse direction becomes sufficiently active to dominate the perception of true rotation in the form of competition. The length of time required to see reverse rotation indicates that the nerve adaptation of a detector that responds to true rotation must occur before a weakly stimulated rotation-backed detector can contribute to perception.

Some little doubt about the results of Kline et al. (2004) maintains discrete-frame theory. These doubts include the findings of Kline et al. In some observers more examples of simultaneous reversal of different parts of the visual field than were expected by chance, and found in some observers the difference in the distribution of the time period of reversal of the expected pure competition process (Rojas, Carmona-Fontaine, LÃƒÆ'Ã‚Â³pez-CalderÃƒÆ'Ã‚Â³n, & amp; Aboitiz, 2006).

In 2008, Kline and Eagleman pointed out that the reversal of the ilus of two spatial overlapping motions can be felt separately, providing further evidence that the reversal of illusionary motions is not caused by temporal sampling. They also show that the motion of the inversion of illusion occurs with non-uniform and non-periodic stimuli (eg, abrasive spinning belt), which also can not be compatible with discrete sampling. Kline and Eagleman instead propose that the effect resulted from "over-effect motion", which means that the movement after effect becomes superimposed on real motion.

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Dangers

Since this illusion can give to a moving machine, it is recommended that single phase lighting be avoided at workshops and factories. For example, a factory powered from a single phase supply with basic fluorescent lighting will have a flicker twice the main frequency, either at 100 or 120 Hz (depending on the country); thus, any rotating engine at this frequency multiplier may appear to be non-rotating. Seeing that the most common types of AC motors are locked in electrical frequencies, this can pose considerable harm to lathe operators and other rotating equipment. Solutions include spreading the illumination through a full 3 phase supply, or by using a high frequency controller that moves the lamps at safer frequencies. Traditional incandescent bulbs, which use filaments that shine continuously with only small modulation, offer other options as well, albeit at the expense of increased power consumption. Smaller incandescent lamps can be used as task lighting on equipment to help combat this effect to avoid operating costs of larger incandescent bulbs in the workshop environment.