One of the reasons for the popularity and resilience of what is today referred to as the “persistence of vision” theory is that it mistakenly provides a simple explanation for two distinct perceptual phenomena. The first is flicker fusion, which is the impression that an intermittent light source is continuous (Colman, 2015). This occurs when a light source’s frequency exceeds the critical fusion threshold rate which is between 55 and 60 Hz (Woo & Rieucau, 2011). The second phenomenon is the illusion of cinematic motion, which scientists call: “apparent movement” or “apparent motion” (Colman, 2015). Joseph and Barbara Anderson (1978; 1998) have critiqued the “persistence of vision” theory in two papers, asserting its inadequacy in explaining cinematic motion. While their scientific arguments were clear and their historical analysis was thorough, it is worth revisiting the subject because the theory based on Joseph Plateau’s (1829, 1835) scientific work conducted nearly 200 years ago continues to persist in the 21st century (see e.g. Fischer, 2022 and Mitenbuler, 2020). Moreover, our understanding of motion perception mechanisms has progressed in the past twenty years, and the unique nature of animated motion was not described.
The principal idea behind “persistence of vision” posits that the retina can retain an afterimage of each film frame long enough to blend with the subsequent image. The fusion of these successive afterimages eliminates projector flicker and creates cinematic movement (Konigsberg, 1997). The theory has long cited afterimages and light streaks as evidence of its validity (Marey, 1899, 23; Sadoul, 1948; Plateau, 1829; d’Arcy,1765), see figure 1. Is it possible that these visual phenomena play a role in motion perception? The short answer is no, because as Zacks (2014, p. 147) explains: “[…] fused images are not moving images.” Afterimages are static and, if blended, produce a collage effect rather than smooth motion (Anderson and Anderson, 1993).
The term “persistence of vision” has vanished from scientific literature due to its association with outdated concepts. Nevertheless, its underlying concepts endure, as seen in the acceptance of the idea that images briefly linger in the visual system, a phenomenon now referred to as visible persistence (Öğmen and Herzog, 2016). Furthermore, according to the Atkinson-Shiffrin model of human memory, visible persistence is associated with iconic memory, which stores “the short-lasting, detailed representation of a briefly presented stimulus” (Teeuwen et al., 2021). However, iconic memory and visible persistence do not contribute to motion perception and may even hinder it (Öğmen and Herzog, 2016).
So, how do we see real or cinematic movement? Researchers acknowledge at least two interconnected perceptual systems that process different forms of motion information (Allard & Arleo, 2022; Lu & Sperling, 2001; Park & Tadin, 2018). Short-range or first-order motion, fast and sensitive to motion energy, process low-level information based on luminosity as objects move across the visual field. Short-range motion appears naturalistic and smooth and occurs when there is little spatial and temporal distance between stimuli (Braddick, 1980). Scientists believe that since short-range apparent motion appears naturalistic, it is processed and perceived like real motion (Anderson, 1998).
Long-range or second-order motion occurs when there is a significant spatial and temporal gap between the appearance and disappearance of stimuli. While it is not disturbing, like flicker or stroboscopic motion, this form of movement lacks naturalism and exhibits somewhat robotic characteristics that can be observed in the moving lights on a cinema marquee or a neon sign, as illustrated in the following video. Because long-range and second-order systems track visual features across space and time, they must rely on higher-level mechanisms, including memory and selective attention (Burr & Thompson, 2011; Cavanagh, 1992; Lu & Sperling, 2001).
How do these types of systems operate in film? Live-action films display naturalistic short-range apparent motion because the frame rate ensures that a moving object’s positions are very close from one frame to another. On the other hand, animation uses both long-range and short-range apparent motion. A cinematic or rough animation’s somewhat mechanical movements can be described as second-order or long-range apparent motion because the drawings are far apart, see figure 2.1. Conversely, an animator will utilize first-order or short-range motion to produce smooth movements by ensuring the in-betweens overlap, see figure 2.3. When the positions of an animated sequence are not close enough to produce smooth first-order motion and are not far enough apart to be perceived as second-order motion, the movement is both disturbing and stroboscopic, see figure 2.2. I have animated these three kinds of motion in the following video. To avoid producing jittery motion, animators add images to fill in the space between their in-betweens. This technique, which I call bridging the gap, only works when the movement is slow because adding images slows the action. To reduce strobing when the movement is fast, one can increase the frame rate, apply motion blur, and use speed lines as shown here. Alternatively, one can, as Lasseter (1987) has suggested, stretch a moving object so that its shape overlaps from one frame to the next, a method that is at the heart of stretch and squash, the first of 12 principles of animation formulated by Disney animators Ollie Johnston and Frank Thomas (1981).
Even though the terms have fallen out of favor, describing cinematic movements as either “long-range” or “short-range” remains relevant because the difference is easily understood by animators who are familiar with timing and spacing (Williams, 2001). More importantly, the underlying psychophysical principles behind first-order and higher forms of motion perception are too complex to explain briefly. So, although short-range and long-range are somewhat reductive, they are a simple and accurate distinction that can be used in the animation studio and the classroom.
References
Allard, R., & Arleo, A. (2022). The false aperture problem: Global motion perception without integration of local motion signals. Psychological review, 129(4), 732. https://hal.archives-ouvertes.fr/hal-03426654/document
Anderson, J. D. (1998). The Reality of Illusion: An Ecological Approach to Cognitive Film Theory. Southern Illinois University Press.
Anderson, J. D., & Anderson, B. (1993). The Myth of Persistence of Vision Revisited. Journal of Film and Video, 45(1), 3-12. https://www.jstor.org/stable/20687993
Anderson, J. D., & Fisher, B. (1978). The Myth of Persistence of Vision. Journal of the University Film Association,30(4), 3-8. https://www.jstor.org/stable/pdf/20687445.pdf
Braddick, O. J. (1980). Low-level and high-level processes in apparent motion. Philosophical Transactions of the Royal Society of London. B, Biological Sciences, 290(1038), 137-151. https://doi.org/10.1098/rstb.1980.0087
Burr, D. C., & Thompson, P. (2011). Motion psychophysics: 1985–2010. Vision Research, 51(13), 1431-1456. https://doi.org/10.1016/j.visres.2011.02.008
Cavanagh, P. (1992). Attention-Based Motion Perception. Science, 257(5076), 1563-1565. https://www.jstor.org/stable/pdf/2879947.pdf
Colman, A. M. (2015). A Dictionary of Psychology (Fourth ed.). Oxford University Press, USA.
Fischer, P. (2022). The Man Who Invented Motion Pictures: A True Tale of Obsession, Murder, and the Movies. Simon and Schuster.
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Mitenbuler, R. (2020). Wild Minds: The Artists and Rivalries That Inspired the Golden Age of Animation. Atlantic Monthly Press.
Park, W. J., & Tadin, D. (2018). Motion Perception. In J. T. Serences (Ed.), Stevens’ Handbook of Experimental Psychology and Cognitive Neuroscience (pp. 418-487). https://doi.org/10.1002/9781119170174.epcn210
Plateau, J. (1829). Dissertation sur quelques propriétés des impressions produites par la lumière sur l’organe de la vue [Dissertation, Université de Liège]. Publié chez H. Dessain, Imprimeur-Libraire, Place du Palais, Liège. http://hdl.handle.net/2268/501
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Woo, K. L., & Rieucau, G. (2011). From dummies to animations: a review of computer-animated stimuli used in animal behavior studies. Behavioral Ecology and Sociobiology, 65(9), 1671-1685. https://link.springer.com/article/10.1007/s00265-011-1226-y
Philippe Vaucher is a Montréal-based animator, filmmaker and professor. By uncovering the cognitive roots of Disney animators Ollie Johnston and Frank Thomas’ twelve principles of animation, he hopes to better understand the art form he loves. Throughout his film career, he has experimented with various animation techniques and has sought to combine traditional media with digital practices. His independent creations include short films and music videos. His latest film, The Well (2013), has won two international awards. He currently teaches animation, cinema and storyboarding at the Université du Québec en Abitibi-Témiscamingue’s Montréal campus.