The phenomenon of persistence of vision (POV) is central to the conceptualisation and pedagogy of animation. There exists however controversy between film/animation theories and empirical science as to the parameters of this phenomenon. POV is classically seen as the phenomenon where the illusion of motion is experienced by rapidly displaying a sequence of slightly different images.
Figure 1. Classic POV.
This term, however, has been criticised as an oversimplification, with voices in scientific circles arguing that other more likely explanations such as the Phi (Φ) Phenomenon (PP) or Short-range apparent motion (SRAM) provide a more scientific grounding for this phenomenon. The PP (Figure 1) describes the experience of motion (objectless or pure motion) between adjacent still images presented in alternation with relatively high frequency (frame rate). The SRAM (Figure 2) refers to the experience of movement with visual stimuli that are placed in close proximity with each other. The theory behind this being that the brain processes motion differently for actual motion (real-world movement) and apparent movement (cinematic movement).
I wonder if the focus of the scientific perspective may be more upon the operational dimension of “flicker” and a viewer’s ability to be aware of frame substitution, and not the subjective experience of movement itself. The basis of the argument for the PP and SRAM is based on empirical data relating to refresh rates of stimuli/frame rate (Anderson & Anderson, 1993, p. 6). This position isn’t really satisfying with the only justification, beyond frame rate, being a “complex set of transformations performed by the human perceptual system” (Anderson & Anderson, 1993, p. 8) – a convenience that does little to further our understanding of the problem at hand.
The subjective bother of refresh rate/flicker may be better explained in terms of electricity and the balance of cost to benefit. Edison and Tesla, in developing alternating current (A/C) electricity, undertook extensive testing on human subjects to resolve the flicker problem of the electric lightbulb. If the frequency of electricity was too low – the consumer was aware of the flicker – the experience of the darkness between bursts of light due to the sinusoidal current. If the frequency was too high, the flicker was eliminated but higher frequency electricity was progressively more expensive to produce. The cost-to-benefit balance for the frequency of electricity to have a subjectively non-annoying lightbulb fell at around 48Hz (50Hz was adopted in 80% of the world and the remainder using 60Hz). This frequency, when used for the mechanism of cinema shutters (and eventually of televisions), divides by 2 for the 1 frame of shuttered black (Figure 4) giving the 24, 25 & 30 frames per second ranges we all know of cinema/television – producing a non-irritating experience of movement.
Figure 4. Flicker from difference frequencies.
I argue that a phenomenological perspective on POV offers an alternative to these theories. When you look at an image of an object “off balance” your intuition prepares you to see that the object will move and fall.
Figure 5. Graceful (left), Self-Sufficient (right).
In general, we all have this kind of intuition, based on an accumulation of prior experiences of this kind of movement before. Phenomenology describes intuition as a form of temporal conscious awareness.
When the next sequential image is presented, the experience is pleasant because it re-enforces that accumulation of prior experiences. If it were to suddenly fly up in the air or snap straight to the ground, it would appear odd, magical at best, but more likely, uncanny, suspicious or broken, not intuitive. This intuition of the nature of motion is something that the French philosopher Henri Bergson called “Grace”. Bergson describes grace in terms of the ‘effortlessness’ of a visual experience – the spectator’s conscious awareness of the nature motion. With a graceful image, subsequent movements are felt in advance. The image speaks of its past, present and future.
“At first [grace] is only the perception of a certain ease, a certain facility in the outward movements. And as those movements are easy which prepare the way for others, we are led to find a superior ease in the movements which can be foreseen, in the present attitudes in which future attitudes are pointed out and, as it were, prefigured. If jerky movements are wanting in grace, the reason is that each of them is self-sufficient and does not announce those which are to follow. If curves are more graceful than broken lines, the reason is that, while a curved line changes its direction at every moment, every new direction is indicated in the preceding one. Thus, the perception of ease in motion passes over into the pleasure of mastering the flow of time and of holding the future in the present” (Bergson, 2001, p. 6).
This is especially apparent in the practical experience of an animator’s own ‘spacing and timing’. When the spacing and timing are graceful, there are no ‘walls’ (sudden frozen motion) or ‘pops’ (sudden unnatural jumps). If the spacing and timing are out, the motion appears jerky, and the illusion of life is lost. In the worst-case scenario of Bergson’s ‘self-sufficient images’, the POV may fail altogether. Grace is present within, and in-between static frames. Intuition is effortless and we all do it all the time whether looking at real-world or cinematic movement (i.e. the experience of a movement in a sequence of graceful images).
Thus, the phenomenological approach offers an alternative new path to explore POV.
Anderson, J., & Anderson, B. (1993). The Myth of Persistence of Vision Revisited. Journal of Film and Video, 45(1), 3–12. JSTOR.
Bergson, H. (2001). Time and free will: an essay on the immediate data of consciousness. Dover Publications.
Jack Parry is a researcher at Swinburne University in Melbourne Australia. His research focuses on the interdisciplinary interpretation of philosophy, in particular phenomenology and process philosophy. He employs an unusual methodology called eidetic animation, where he imbibes and meditates upon complex ideas in order to rearticulate them as moving images.