22/04/2017

Every Year In Film #2 - The Persistence Of Vision

Thoughts On: Stroboscopes, Phenakistoscopes & Zoetropes


Having only touched on the conceptual origins of film and an incentive for cinema, we will attempt to delve deeper by taking a look at a few 19th century inventions.

    

Before getting into films and years, we should conclude the first post in Every Year In Film. In the previous post, we touched on the origins of cinema in a conceptual sense, ending on the idea that cinema essentially views movement as a language and so means to communicate through the manipulation of space and time. This all began the moment humans tried to communicate imagery through gestures and sound. A more satisfactory and tangible beginning of cinema, however, can certainly be found in ancient cave paintings - the oldest of which are at least 35,000 years old - that mean to imply movement:


This painting, once we consider how cinema functions, is certainly a form of 'film'. And this is hopefully what we'll end up understanding having concluded our perceptual preemptive to the Every Year In Film series.

The least abstract place to start talking about film would be the early 1830s. In 1830 Michael Faraday, a British scientist who conducted pivotal experiments in electromagnetism, presented a paper called On a Peculiar Class of Optical Deceptions. This paper overlapped with the research of Joseph Plateau, a Belgian Physicist, who had also written about optical illusions in rotating wheels (all of which are expansions and deeper explorations of work by Peter Mark Roget - a man most famous for compiling the first modern thesaurus). All of this research, and with some communication between Faraday and Plateau, led to the invention of the phenakistoscope.


Otherwise known as a spindle viewer, the phenakistoscope is two spinning disks attached to a stick. One disk has slits along its inner or outer circumference, and when you look through these slits at the other disc, you will see the image on it move...


Plateau, who perfected this invention, published it in 1833. However, simultaneously in Austria, Simon von Stampfer invents a very similar device that functions in the same manner as the phenakistoscope - Stampfer called these Stampfer Discs or Stroboscopes.


He, like Plateau, knew the work of Faraday, but published his work in 1831. His variation of the phenakistoscope, which you would look into a mirror to see function, was made independently and would have worked just like Plateau's...


As apart of his work, Stampfer mentioned a cylindrical version of his stroboscope. And having seen Plateu's phenakistoscope this was independently invented by William George Horner, a British mathematician. Horner called this cylindrical stroboscope a Daedaleum.


This functions just like the stroboscope and phenakistoscope in that you'd look through the slits to see the image laced on the inside move...


However, Horner never published his Daedaleum, he only invented it in 1934. It wasn't until William Ensign Lincoln invented and published the Zoetrope in 1865 that we had the official cylindrical stroboscope - which was essentially just a Daedaleum.

These three devices - a phenakistoscope, stroboscope and zoetrope - all function in around about the same way. To understand them you then only have to consider an image such as this:


There are two ways to produce an image like this. The first would be to take continuous pictures of this snowboarder as he flies through the air and then composite them into one image using Photoshop. Similarly, you may use a device called a stroboscope (not the one we've been talking about so far - an electric stroboscope)...


... which rapidly flashes light, allowing you to take a picture of blurred movement in one frame with a low shutter speed.


Side note, if you want more of an explanation on these electronic stroboscopes and how they're used, there are two videos here: video 1 & video 2.

What we are seeing in a Zoetrope or a machine alike is a mechanical version of a strobe effect; of that snowboarder flying through the air.


In such, instead of photographing and cutting all the images of a snowboarder into one image, within a Zoetrope, you may place all of your images on a strip and produce what we may basically call a flip book effect:


You do this by taking that strip of images, spinning them rapidly and looking at them with dark intervals (which separate and distinguish them). This is why the slits are so important in all of these devices.


Without slits, you'd just be seeing a blur of images as you would only be watching a disc spin, hence seeing the white spaces between images instead of many snapshots of a disc spinning - all of those snapshots, by design, matching up with the rotation of the image so you may see, for example, a figure skipping. The slits then smooth out the spinning by, in the simplest terms, only showing a brief shot of the disc, confusing the eye and allowing it to think that an image moves. So, whether you look to the flip book, the stroboscope or even a film, you will always see something interrupting each frame - the turning of a page, the dark space between slots or a shutter. Spun at the right speed, for film, as we all know, this is 24 frames per second, and this carries over to devices like the stroboscope (over 15 slot passings a second), you have the illusion of movement. The reason for this number, 24 frames, comes down to your visual cortex.


The visual cortex is the region of your brain that is linked to your eye. These two elements communicate with chemical reactions; the eye gaining information from light hitting the retina...


... and passing it along to the brain through nerves. The eye gathers this information and passes it along to visual cortex where it is held it for approximately 1/15th (one fifteenth) of a second. And this is where we start to understand where 24 frames a second comes from. The brain can essentially take 15 snapshots of the world in 1 second and can understand that they are individual and unmoving entities. So, if you show someone a film, flip book or even a Zoetrope at a slow rate so that they only see 12 pictures in a second, they will see that it's just single photos being shown one after another like a slide show. However, if you spin the zoetrope faster, play the film quicker, flip the book at a greater rate, and show the eye more than 15 individual images per second, the brain will start seeing continuous motion. This comes back to the visual cortex holding information for one fifteenth of a second; the brain simply can't keep up with 17, certainly not 24, images being show in one second and so interprets the transitions as fluid movement.

This is generally known as The Persistence Of Vision. However, this terminology and theory is incorrect. The theory of The Persistence Of Vision assumes that the eye itself holds onto information for a fraction of a second and so allows images to blur into one another. This was disproved in 1912 by Max Wertheimer yet you will still hear about this theory to this day. The reason why the theory is incorrect is multifaceted. Firstly, and as we discussed, the brain, not the eye, retains information. Secondly, the eye is not a camera and so must be described in more complex terms. Even though we used words like 'snapshot' to discuss a packet of information (light; photons) hitting the eye, this is a poor description of the physiological process as there is a continuous stream of information hitting the eye that doesn't just get caught in a photo and handed to the visual cortex. Moreover, and as we said, images can't just blur into one another and be perceived as fluid motion. For example, pay attention to the beginning of the gif:


Before we look through the slots, the birds are incoherent images - this is what images blurred together looks like. These three ideas all directly contradict the theory of Persistence Of Vision, hence disproving it. There are other, much better explanations of this to be found, but this is the gist of things from someone who is not a neurologist - as with most things in this post.

So, if The Persistence Of Vision is the wrong term, how do we describe this process of seeing many fluttering images with dark intervals in between them as moving? There are two terms: phi phenomenon and beta movement. Phi phenomenon describes this image:


You probably know how this functions: those yellow lights are just turning on and off in sequence. However, when you look at it, it seems like the light itself is jumping from point to point - as if it's moving. This is your brain being tricked by, or making sense of, this light pattern; it makes you believe that independent lights flashing are in fact one light moving through space.


Beta movement is a very similar paradigm, but, instead of describing lights jumping through space, this function describes the perception of moving bodies. So, as you could infer, there aren't 3 dots moving like a snake around this image. There's 12 dots and their lights just turn on and off in sequence. However, you perceive that there is on singular body; that a shape is retained through space when there isn't a shape at all. This is beta movement.

Both of these theories are the scientific and true explanation of why flashing frames, when moving above (this will work, though not very well, when the frame rate is lower, but close to) 15 frames a second. This then begs the question, how has 'The Persistence Of Vision' remained relevant after a century of being debunked? In short, it's a simpler explanation and is a much better term. So, every time you say or hear "The Persistence Of Vision", just know you basically mean phi phenomenon and beta movement when you are describing why you don't see black frames between each frame of a film, instead, moving images.

Having covered the general history and science of pictures in motion, we have come ever closer to cinema itself. However, it could be argued that we are already talking about cinema when we mention zoetropes, stroboscopes and so on. This is simply because cinema is a trick of perception - as we now understand. And as we concluded in the previous post, cinema is movement as a language, is communicating through the manipulation of space and time. If we were to retain this definition and understand that motion perception, when it is to be controlled and manipulated by a person or artist, is just an illusion, then any implied movement is cinema. After all, to quantify cinema as just a frame rate is redundant and a truly lacking definition. To imply that cinema is the illusion of movement at 24 frames a second not only ignores the substance and play with its form, but also says that slow motion doesn't count, that neither do silent films (which often came in at varying rates - between 12 and 40 fps) and that neither do Scorsese's or Truffaut's iconic freeze frames. And so this is why cave paintings such as this...


... can and should be considered a form of cinema. Cinema is just communication through motion, and so, though the material and means of viewing the cave art is different, seeing all motion as some kind of cinema allows you to grip both where cinema comes from, what it is and why it came to be as best as you can.

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