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  • Take a series of still, sequential images.

  • Let's look at them one by one.

  • Faster.

  • Now, let's remove the gaps,

  • go faster still.

  • Wait for it...

  • ...bam!

  • Motion!

  • Why is that?

  • Intellectually, we know we're just looking

  • at a series of still images,

  • but when we see them change fast enough,

  • they produce the optical illusion

  • of appearing as a single, persistent image

  • that's gradually changing form and position.

  • This effect is the basis for all motion picture technology,

  • from our LED screens of today

  • to their 20th century cathode ray forebearers,

  • from cinematic film projection

  • to the novelty toy,

  • even, it's been suggested,

  • all the way back to the Stone Age

  • when humans began painting on cave walls.

  • This phenomenon of perceiving apparent motion

  • in successive images

  • is due to a characteristic of human perception

  • historically referred to as "persistence of vision."

  • The term is attributed

  • to the English-Swiss physicist Peter Mark Roget,

  • who, in the early 19th century,

  • used it to describe a particular defect of the eye

  • that resulted in a moving object

  • appearing to be still when it reached a certain speed.

  • Not long after,

  • the term was applied to describe the opposite,

  • the apparent motion of still images,

  • by Belgian physicist Joseph Plateau,

  • inventor of the phenakistoscope.

  • He defined persistence of vision

  • as the result of successive afterimages,

  • which were retained and then combined in the retina,

  • making us believe that what we were seeing

  • is a single object in motion.

  • This explanation was widely accepted

  • in the decades to follow

  • and up through the turn of the 20th century,

  • when some began to question

  • what was physiologically going on.

  • In 1912, German psychologist Max Wertheimer

  • outlined the basic primary stages of apparent motion

  • using simple optical illusions.

  • These experiments led him to conclude

  • the phenomenon was due to processes

  • which lie behind the retina.

  • In 1915, Hugo Munsterberg,

  • a German-American pioneer in applied psychology,

  • also suggested that the apparent motion

  • of successive images

  • is not due to their being retained in the eye,

  • but is superadded by the action of the mind.

  • In the century to follow,

  • experiments by physiologists

  • have pretty much confirmed their conclusions.

  • As it relates to the illusion of motion pictures,

  • persistence of vision has less to do with vision itself

  • than how it's interpreted in the brain.

  • Research has shown that different aspects

  • of what the eye sees,

  • like form,

  • color,

  • depth,

  • and motion,

  • are transmitted to different areas of the visual cortex

  • via different pathways from the retina.

  • It's the continuous interaction

  • of various computations in the visual cortex

  • that stitch those different aspects together

  • and culminate in the perception.

  • Our brains are constantly working,

  • synchronizing what we see,

  • hear,

  • smell,

  • and touch

  • into meaningful experience

  • in the moment-to-moment flow of the present.

  • So, in order to create the illusion

  • of motion in successive images,

  • we need to get the timing of our intervals

  • close to the speed at which our brains process the present.

  • So, how fast is the present happening according to our brains?

  • Well, we can get an idea

  • by measuring how fast the images need to be changing

  • for the illusion to work.

  • Let's see if we can figure it out

  • by repeating our experiment.

  • Here's the sequence presented

  • at a rate of one frame per two seconds

  • with one second of black in-between.

  • At this rate of change

  • with the blank space separating the images,

  • there's no real motion perceptible.

  • As we lessen the duration of blank space,

  • a slight change in position becomes more apparent,

  • and you start to get an inkling of a sense of motion

  • between the disparate frames.

  • One frame per second,

  • two frames per second,

  • four frames per second.

  • Now we're starting to get a feeling of motion,

  • but it's really not very smooth.

  • We're still aware of the fact

  • that we're looking at separate images.

  • Let's speed up,

  • eight frames per second,

  • twelve frames per second.

  • It looks like we're about there.

  • At twenty-four frames per second,

  • the motion looks even smoother.

  • This is standard full speed.

  • So, the point at which we lose awareness of the intervals

  • and begin to see apparent motion

  • seems to kick in at around eight to twelve frames per second.

  • This is in the neighborhood

  • of what science has determined

  • to be the general threshold of our awareness

  • of seeing separate images.

  • Generally speaking, we being to lose that awareness

  • at intervals of around 100 milliseconds per image,

  • which is equal to a frame rate of

  • around ten frames per second.

  • As the frame rate increases,

  • we lose awareness of the intervals completely

  • and are all the more convinced

  • of the reality of the illusion.

Take a series of still, sequential images.

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B1 中級

TED-Ed】アニメーションの基本。動きの錯視 - TED-Ed (【TED-Ed】Animation basics: The optical illusion of motion - TED-Ed)

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    阿多賓 に公開 2021 年 01 月 14 日
動画の中の単語