The Biology Behind Movies

Movies work because of a biological phenomenon known as "flicker fusion." This is the ability of the human eye and brain to perceive rapidly changing individual still pictures as one continuous motion, creating the illusion of movement.

Flicker Fusion

This phenomenon has been studied for almost two centuries. It was first formally presented by Peter Mark Roget (best known for Roget's Thesaurus) in 1825, in his paper entitled "Explanation of an Optical Deception in the Appearance of the Spokes of a Wheel Seen through Vertical Apertures," published by The Royal Society in London. Roget described the optical illusion now known as "persistence of vision" where an image continues to appear in one's vision after the exposure to the original image has ceased. This allows for a sequence of separate images to create the illusion of motion.

Roget's study of this phenomenon laid the foundation for the invention of the thaumatrope, a toy that exploits the persistence of vision. A thaumatrope is a small disc or card with a picture on each side, attached to two pieces of string. When the strings are twirled quickly, the two pictures appear to blend into one due to the persistence of vision.

Before the magic of movies could captivate audiences worldwide, however, it first had to be invented. This accomplishment is often attributed to Thomas Edison and his assistant William Kennedy Laurie Dickson. In the 1890s, they developed the Kinetograph, an early motion picture camera, and the Kinetoscope, a single-viewer display device.

Dickson was pivotal in the development process, designing the sprocket system that allowed the film strip to be moved through the camera and viewer at a regular pace. This mechanical innovation, combined with the principle of flicker fusion, made possible the creation of the first motion pictures.

Movies, however, were not popularized by Edison and Dickson; that was achieved by the Lumière brothers in France. Auguste and Louis Lumière invented the Cinématographe, a device that could capture, process and project motion pictures. Their public screening of short films in 1895 and 1896 – often recognized as the birth of cinema – mesmerized audiences and ignited a global fascination with the magic of moving images.

Biology is the Key

But how does biology really make movies work?

When watching a movie or animation, the individual pictures or frames are presented to us at a rate that is faster than our flicker fusion threshold. This means that our brains do not perceive the individual images as separate, but instead, they blur together into what appears to be a continuous motion. The projector or digital display is, in essence, tricking our brains into seeing movement where there is none. Each individual frame of a movie is a static image, and the motion that we see is a psychological and physiological illusion created by the quick succession of these images.

Our brains, however, do more than just passively receive and process visual data. They employ prior knowledge and experience to anticipate and interpret what we see, filling in gaps and making predictions. Cognitive scientists refer to this as the “predictive coding theory.” It explains why we can understand blurry or obscured images in movies, anticipate plot developments and interpret complex cinematic techniques – our brain is constantly making educated guesses based on what it has learned from past experiences.

A Grand Illusion

Every film you've watched, every video clip on your smartphone, every pixelated movement on your computer screen – it's all an illusion. Our perception of motion in these instances is a trick played on our eyes and brains.

Today, as we stand on the cusp of emerging technologies like virtual and augmented reality, it's worth being aware of the intricate biological dance between our eyes and brains that makes movies possible.