The Fast Movement Of Briefly Flashed Images In An Animated Motion Picture Produces What Effect?

Lectures: Visual Perception 8

The Moving Prototype

Rod Munday

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Alarm

Approximately i in 4 thousand people suffers from Photosensitive Epilepsy (PSE). PSE is sensitivity to flickering or intermittent calorie-free stimulation and visual patterns. If yous showtime to feel sick when looking at this page, practise not persist as it is possible that you suffer from PSE and prolonged exposure to some of these images could result in a seizure.

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Introduction

Our focus here is on the perception of motion pictures. Every bit David Cook remarks, move pictures occupy a central position in our lives and yet few people sympathize how they work, then much so that "If we fabricated an illustration with exact language we should be forced to consider ourselves barely literate" (Cook 1981, Xv).

Information technology is thought that humans perceive move due to processes that occur both in the eye and in the brain. Low-cal falling on a set up of receptors in the centre at one example and on another nearby set in the side by side case successively stimulates adjacent retinal points, which is how we come across motion with the eye. Nonetheless, cortical cells in the brain respond to these changes of light which is how we know something moves (Haber & Hershenson 1980, 208).

All too often, we hash out movement perception every bit though all we had to consider was the perception of a moving object past a static subject area. (Every bit shown in session 3), this is hardly ever the case. Our vision is very well adult, because as perceivers, we take a tendency to move around a lot. Yet we are still able to perceive other moving things in a seemingly static world (ibid.). These twin faculties of retinal stabilisation and motion detection gives u.s. an extraordinary power to recognise moving objects, even if we are given next to no information about them. For example (as noted in session seven) the Swedish psychologist Gunnar Johansson showed an arrangement of lights placed on each of the major joints of a man body was immediately recognised as a person every bit long every bit the person moved (Miller 1990, 189). Incidentally Johansson'south findings were later exploited to form the basis of motion capture in film like King Kong (Peter Jackson, 2005) and The Polar Express (Robert Zemeckis, 2004) (for more information about motion capture, see Sturman, 1999).

The limitations of seeing movement

Despite our amazing ability to recognise moving shapes, our perception of movement falls within certain thresholds. Movement which is either as well fast of too slow is not detectable. At one extreme we are unable to see a bullet fired from a gun, at the other we are unable to detect the motility of an 60 minutes hand going round a clock face. It is also possible to fool the brain into thinking there is movement where actually none exists. Such phantom movement is created by lookin at something constantly in motion, like a waterfall, and then looking at something which is not moving. If you exercise this, y'all will find that the stationary scene appears to exist moving in the contrary direction to the waterfall, i.e., upwardly. This illusion is called "the waterfall illusion." I example was shown in session six; another variation of it is illustrated in Fig i.

Fig one - Instructions: stare at the spiral for near 20 seconds, and so stare at the pattern.

In a study that looked at similar screw discs Spigel (1962) it was reported that all observers saw the spiral move in the reverse direction. The later on effect lasted ten seconds on average.

Moving Pictures

The way that nosotros perceive motility in film is different to the way nosotros perceive moving objects in real life, since film images practice non really motion at all. In fact an imaging technology has however to be invented that can stand for 'true motion'. The motion represented in television, films, computer games, multimedia presentations etc. is known equally credible motion. Credible move is created past displaying a series of consecutively photographed still images in quick succession.

Apparent motion in film projection

Let'due south wait in more detail at how the illusion of apparent move is created in cinema projection. When y'all look at a strip of picture show you tin come across that it is fabricated up of a serial of nonetheless pictures (chosen frames) which are arranged vertically down the length of the film. Notwithstanding, just running this moving picture through a projector would not by itself create the illusion of movement; in fact the result would be a meaningless blur. So the mechanism of the projector is constructed in such a way that each frame is paused momentarily in front of the projector'south light source. The gap between frames is also marked by an equally brusk period of blackness. This is created by a device chosen a shutter. In Fig. 2, this shutter is represented equally a twin blade rotating disc that resembles the blades of a fan.

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Fig 2 - A flick projector

The shutter blades laissez passer over the axle emitted by the lamp, blanking the light out at regular repeated intervals and effectively turning the projector low-cal into a kind of strobe. The strobing of the projector is synchronised with the rate that the picture show is sprocketed in front of the light source. If a projector were slowed sufficiently, nosotros would exist able to perceive the shutter activity quite easily--as a succession of picture frames and black frames. But when the projector is speeded upwards, information technology get progressively harder to encounter the black frames. Thus an increased frame charge per unit gives increased allegiance to the illusion of movement, until, after a sufficiently high frame charge per unit is reached, the strobing becomes imperceptible.

Flicker Fusion

Equally nigh people know, films are projected as 24 frames a second - the filmmaker Jean Luc Goddard called moving picture "truth 24 times a 2nd" Weekend (1968). Notwithstanding, while film may be photographed at 24 frames a second (or 24 Hertz), in that location are 2 shutter rotations for every frame, which doubles the projected frame charge per unit to 48 Hertz, thus eliminating the flicker. The technical term for this is 'flicker fusion,' Neon lighting besides work on the principle of flicker fusion, because neon lights flicker on an off fifty times a second (in the UK).

Wagon Bicycle illusion

An of import characteristic of the perception of apparent motion is that information technology is pre-conscious, which means that unlike, say, the codes of continuity editing ( to be outlined in session x) you cannot choose whether you run into it or not. Therefore the fact that it is, in part, based on cognitive processes in the brain gets very hands overlooked. However, a famous cinematic illusion that draws our attention to the constructed nature of moving pictures is the wagon wheel illusion. If you oasis't seen the wagon wheel illusion pay shut attention the next time yous are watching a western.

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Fig 3 - Railroad vehicle wheels

You volition notice that the wheels of the covered wagons appear to be either turning backwards or even oscillating between forrad and backwards motion depending on the speed that the wagon is moving. (This volition be meliorate illustrated in the lecture than in Fig. 3!) The wagon wheel illusion occurs because the frequency at the wheels was turning when information technology was photographed interferes with the speed at which the moving picture is being shuttered through the projector. In other words the illusion is an artifact of the strobing cinematic image. This illusion really occurs with all types of wheels in films, only information technology is especially noticeable with railroad vehicle wheels, because the length and thickness of their spokes, which emphasise the illusion. But the odd matter is that some people written report that you can see the wagon wheel illusion in real life, for instance if y'all sit in the rider seat of a moving car and expect at the wheels of another moving vehicle. Recent studies have confirmed this equally a genuine phenomenon - for case encounter, Kline et al. (2003), Van Rullen & Koch (2004), Purves, Paydarfar and Andrews (1996). This has interesting implications for theorising about the way we detect bodily motion in the encephalon, for it suggests that the brain might perceive motion as a series of discreet frames, much similar the frames of motion pictures, although it is not as even so know for sure how this works.

Persistence of vision

Explaining the mechanics of how move pictures work is one affair, but it does not explicate why withal pictures appear to move. In the history of bookish writing on film, by far the largest majority of theorists have chosen to explain credible movement as what is known as 'persistence of vision'. The persistence of vision theory is built on a single hypothesis: when a consecutive sequence of still images is flashed before the eye, each paradigm is merged into a seamless moving continuum, because the brain, or the retina of the eye (proponents of the theory are divided as to which) retains an momentary afterimage of the preceding image, which is and then blended with the next paradigm of the sequence. Here is how the Complete Film Dictionary explains the theory:

Motion pictures are actually a series of still photography that record the successive positions of a subject in movement, Because the eye holds the paradigm of one position after that paradigm disappears from the screen and until the next appears and considering a shutter in the camera blocks out the intermittent movement from one frame to another the successive images seem to alloy into one another creating a continuity of movement. (Koningsberg 1997, 291)

All well and expert, but the persistence of vision theory is actually wrong. For example, Nichols & Lederman (1980) write:

The theory that adult to explain the phenomenon of apparent move has been called the 'persistence of vision,' only perceptual psychologists put forward a dissimilar theory, challenge that virtually every other business relationship to explicate the miracle is wrong and that 'persistence of vision' is nothing more than a myth. (Nichols & Lederman 1980, p96)

Why mention information technology so? Well, because every bit students of picture show and the media y'all will find many references to information technology in some, otherwise, quite authoritative text books. For example, André Bazin marveled at how information technology took so long for the motion picture to come into being "since all the prerequisites had been assembled and the persistence of the image on the retina had been known for a long fourth dimension" (1967).Christian Metz wrote that "motion in the cinema is not a re-presentation, but a presentation, non the re-experience simply the experience of motion" (Metz 7-9). And ironically David Melt, who castigating us for our cinematic illiteracy in the introduction, goes on to cite persistence of vision every bit the reason why pictures appear to motion. So much for cinematic literacy and then! As Nichols and Ledermen remark:

The very persistence with which this 'explanation' has been recited says more about the hermetic and impressionistic world of some film scholarship than it does about the actual mechanisms involved. (Nichols & Lederman, op. cit.)

The fact that persistence of vision is wrong can exist easily proved with a simple demonstration. I yous look at effigy 4, y'all will find that a series of white dots announced to glimmer on and off in sequence against a blue background. You should also notice that a "phantom" dot, the same color as the background, appears to chase around the circle in an anti clockwise direction.

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Fig iv white dot, blue background

The phantom dot ever takes on the colour the background. Then simply to prove this, Fig. 5 shows a phantom white dot chasing around a bluish circle:

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Fig five - blue dot, white background

Now if the persistence of vision is right information technology would follow that the apparent movement of this paradigm would exist due to the after paradigm of the white dot (Fig. 4) or blue dot (Fig. 5). Later on-prototype is actually a very real phenomenon. For example, if you state at the pink triangle of (Fig. 6) for a while and and then stare at the grey space adjacent to it and you should run across the later-image of the triangle - it will plough green, every bit the after image appears equally complimentary colour of the source image.

Fig 6 - Instructions: stare at the triangle for about x seconds, and so stare at the grey foursquare.

At present look at this series of pink dots in a white circle of fig 7.

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Fig seven - pink dot, grey background

The chaser dot is not pink but as in (fig. 4) it takes on the colour of the background. It is possible you see an later on image of the pink dot in this instance, but you find that it actually fights with the movement of the chaser dot. Thus the very hypothesis on which the persistence of vision rests, does not in fact actually account for the movement of this phantom dot - if anything the after image tends to gets in the style of the perception of motion and yous accept to try to ignore it.

Phi Phenomena

The reason the dot appears to movement is because of a set of two illusions that come under the heading of phi phenomena. Phi phenomena were discovered in 1912 by Max Wertheimer, a pioneer of gestalt theory(Wikipedia, www) - run into session 7 for more on gestalt theory. Wertheimer was experimenting with two lamps, turning them off and on in quick succession and noticed that the light appeared to 'jump' from one lamp to the other. 'Phi phenomena' is actually an umbrella term that describes two types of credible movement. 1 of these is the one we have already seen in figures 4, 5 & 7; that is the phantom dot chasing around the circle. Confusingly this is called phi-phenomenon, the singular of a phi phenomena. The other blazon of movement that comes under the heading of phi phenomena (plural) goes by the name of beta move. Beta motility is illustrated in fig. 8, which is exactly the aforementioned paradigm as fig. 4, but with its motion slowed down. However, you will notice that instead of the while dots appearing to be stationary and blinking on and off, that now the dots themselves appear to motility - jumping to fill up the place place vacated by the previous dot. Also you volition also notice that the phantom chaser dot appears to have almost disappeared. .

Fig eight - beta move

The politics of move

In its entry on phi phenomena the Complete Picture show Dictionary is quite condescending. It says:

Like persistence of vision this phenomen[a] has been used to explicate the illusion of movement created by motion pictures; but whereas the former is largely a physiological upshot of the optic fretfulness; the latter is a psychological outcome of the brains operations. See persistence of vision... (op. cit., 293)

It seems rather odd to describe phi phenomena as existence 'psychological', because they are as much physiological as psychological--strictly speaking neuro-physiological (run into Wertheim 1994 & Haber & Hershenson 1980). A expert question to inquire is: if phi phenomena are a amend explanation of apparent motion, why do then many sources nevertheless aspect it to the persistence of vision? In attempting to reply that question information technology may be wise to recall most those theoretical assumptions which are served by a theory that stresses that apparent motility is due to the middle (persistence of vision) as opposed to those served by a theory that stresses the brain'due south involvement (phi phenomena). Joseph Anderson and Barbara Fisher (1993) contend that the phi miracle privileges a more constructivist approach to the cinema (David Bordwell, Noel Carroll, Kirsten Thompson), whereas the persistence of vision privileges a realist approach (Andre Bazin, Christian Metz, Jean-Louis Baudry).

One could peradventure claim that perpetuating the myth of the persistence of vision fabricated it unnecessary to question the psychological and physiological systems that the spectator brings to the perception of the moving images they meet on the screen. Film scholarship founded on an aesthetic tradition (Dyer 1998, 4), which is arguably ill equipped and unprepared to deal with the empiricism inherent in the development of a neuro-physiological theory. In contempo years, however, it has go increasingly apparent that while films themselves may be viewed every bit aesthetic texts, they are texts nevertheless perceived by human beings and interpreted in a social context. Perhaps then the answer to the question, "why does the persistence of vision theory itself persist?", can tell us more almost the politics of academic film criticism that it can about the lack of empirical rigour among film theorists.

References and Suggested Reading

• Anderson, Joseph and Barbara Fisher (1978) 'The Myth of Persistence of Vision.' Journal of the Academy Film Association30 nNo. 4: 3-8. URL http://world wide web.uca.edu/org/ccsmi/ccsmi/classicwork/Myth1.htm [accessed iii/iii/06].
• Anderson, Joseph and Barbara Fisher. "The Myth of Persistence of Vision Revisited," Journal of Pic and Video, Vol. 45, No. 1 (Leap 1993): 3-12. URL http://www.uca.edu/org/ccsmi/ccsmi/classicwork/Myth%20Revisited.htm [accessed 3/3/06].
• Bazin, André (1967) What is Cinema?, Vol. I, Trans. Hugh Gray, Berkeley: Academy of California Press
• Cook, David A. (2004) A History of Narrative Film. New York, Westward. West. Norton & Visitor
• Haber, Ralph Norman and Maurice Hershenson (1980) The Psychology of Visual Perception (second edition). London: Holt, Rinehart and Winston.
• Kline, K. AO Holcombe, DM Eagleman - (2004) "Illusory motion is caused by rivalry, not by perceptual snapshots of the visual field" Vision Inquiry 44, URL http://nba.uth.tmc.edu/homepage/eagleman/papers/KlineHolcombeEaglemanVisRes2004.pdf [accessed three/3/06].
• Koningsberg, Ira (1997) The Consummate Film Dictionary (2nd Edition). London: Bloomsbury.
• Metz, Christian (1991) Film Language: A Semiotics of The Picture palace, trans. Michael Taylor. Chicago: Academy of Chicago Press.
• Miller Jonathan (1990) "Moving Pictures" in Horace Barlow, Colin Blakemore and Miranda Weston-Smith (Eds) Images and Understanding. Cambridge: Cambridge University Printing.
• Nichols, Pecker & Susan J. Lederman (1980) 'Flicker and Move in Motion-picture show' In The Cinematic Apparatus, Teresa de Lauretis & Stephen Heath (editors): NY: St Martin'south Press.
• Purves, Paydarfar and Andrews (1996): 'The Wagon Wheel Illusion In Movies And Reality' In Neurobiology, Vol. 93, pp. 3693 to 3697, URL http:www-users.york.ac.uk/~ta505/PNAS_93_3693.pdf [accessed 10/3/07].
• Sturman, David J. (1999) 'A Brief History of Movement Capture for Computer Grapheme Animation', URL http://www.siggraph.org/didactics/materials/HyperGraph/animation/character_animation/motion_capture/history1.htm [accessed 2/3/06]
• Van Rullen, R. and Koch, C. (2003) "Is Perception Discrete or Continuous?" Trends in Cerebral Sciences, 2003 - klab.caltech.edu URL http://www.klab.caltech.edu/~rufin/OriginalPapers/DiscretePerception.pdf [accessed iii/3/06]
• Wertheim, A.H. (1994) "Movement Perception During Self-Motility: The Direct Versus Inferential controversy revisited". Behavioral and Brain Sciences 17 (2). URL http://world wide web.bbsonline.org/Preprints/OldArchive/bbs.wertheim.html [accessed 2/iii/06]

Image Credits

• Fig. ane, screw and pattern created by Rod Munday, based on an paradigm by Mark Newbold. URL http://dogfeathers.com/java/spirals.html [accessed 9/6/06].
• Fig. 2, film projector diagram taken from, "How Products Are Made", URL http://www.madehow.com/Volume-7/Movie-Projector.html [accessed ix/6/06].
• Fig. 3, animated gif past Rod Munday. Prototype taken from How The Westward Was Won (1962), directed by John Ford, Henry Hathaway, George Marshall and Richard Thorpe. Source for information, Internet Movie Database, [accessed 9/6/06].
• Fig. 4, phi phenomenon white/blue, animated gif created by Rod Munday. Inspired past the coffee applet at URL http://www2.psych.purdue.edu/Magniphi/MagniPhi.html [accessed nine/6/06].
• Fig. 5, phi phenomenon blue/white, animated gif created by Rod Munday. Inspired by the coffee applet at URL http://www2.psych.purdue.edu/Magniphi/MagniPhi.html [accessed 9/vi/06].
• Fig. 6, Pink Triangle, created past Rod Munday.
• Fig. 7, phi phenomenon pink/grey, animated gif created past Rod Munday. This is an adaptation of the "lilac chaser", on Michael Bach's excellent optical illusion site. URL http://www.michaelbach.de/ot/col_lilacChaser/index.html [accessed ix/6/06].
• Fig. 8, beta motion white/blue, animated gif created by Rod Munday. Inspired by the coffee applet at URL http://www2.psych.purdue.edu/Magniphi/MagniPhi.html [accessed 9/6/06].

• Visual Perception 1: Searching for Patterns
  
• Visual Perception ii: The Third Dimension
  
• Visual Perception three: Selectivity and Perceptual Constancy
  
• Visual Perception 4: Cultural and Environmental Factors
  
• Visual Perception five: Individual Differences, Purposes and Needs
  
• Visual Perception six: Context and Expectations
  
• Visual Perception seven: Gestalt Principles of Visual Arrangement
  
• Visual Perception 8: The Moving Image
  
• References and Suggested Reading
  

Source: http://visual-memory.co.uk/daniel/Modules/FM21820/visper08.html

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