Wagon-wheel effect
The wagon-wheel effect is most often seen in film or television depictions of stagecoaches or wagons in Western movies, although recordings of any regularly spoked rotating object will show it, such as helicopter rotors, aircraft propellers and car rims.
A temporal anti-aliasing filter can be applied to a camera to achieve better band-limiting and reduce the wagon-wheel effect.
Artificial lighting that is temporally modulated when powered by alternating current, such as gas discharge lamps (including neon, mercury vapor, sodium vapor and fluorescent tubes), flicker at twice the frequency of the power line (for example 100 times per second on a 50-cycle line).
If by the time the next instance of visibility occurs, the spoke previously at 9 o'clock has moved into the 12-o'clock position, then a viewer will perceive the wheel to be stationary.
If at the second instance of visibility, the next spoke has moved to the 11:30 position, then a viewer will perceive the wheel to be rotating backwards.
Finlay and Dodwell (1987) argued that there are some critical differences between the wagon-wheel effect and beta movement, but their argument has not troubled the consensus.
A similar stroboscopic effect is now commonly observed by people eating crunchy foods, such as carrots, while watching TV: the image appears to shimmer.
He distinguished three forms of subjective stroboscopy which he called alpha, beta, and gamma: Alpha stroboscopy occurs at 8–12 cycles per second; the wheel appears to become stationary, although "some sectors [spokes] look as though they are performing a hurdle race over the standing ones" (p. 48).
Gamma stroboscopy occurs at 40–100 cycles per second: "The disk appears almost uniform except that at all sector frequencies a standing grayish pattern is seen ... in a quivery sort of standstill" (pp. 49–50).
Schouten interpreted beta stroboscopy, reversed rotation, as consistent with there being Reichardt detectors in the human visual system for encoding motion.
They reviewed experiences of users of LSD who often report that under the influence of the drug a moving object is seen trailing a series of still images behind it.
These doubts include Kline et al.'s finding in some observers more instances of simultaneous reversals from different parts of the visual field than would be expected by chance, and finding in some observers differences in the distribution of the durations of reversals from that expected by a pure rivalry process (Rojas, Carmona-Fontaine, López-Calderón, & Aboitiz, 2006[13]).
[14] They also showed that illusory motion reversal occurs with non-uniform and non-periodic stimuli (for example, a spinning belt of sandpaper), which also cannot be compatible with discrete sampling.
[citation needed] Seeing that the most common types of AC motors are locked to the mains frequency, this can pose a considerable hazard to operators of lathes and other rotating equipment.
[15] Traditional incandescent light bulbs, which employ filaments that glow continuously with only a minor modulation, offer another option as well, albeit at the expense of increased power consumption.
