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Are you talking about Critical Flicker Fusion here?


Possibly. (I'm unfamiliar with the term, TIL!) As I dimly recall from last century, we are sensitive to flicker in the coarse-resolution field, but insensitive to non-flickering change outside the fine-resolution field.


Then you're probably familiar with the 24 frames per second cinema standard for projecting films. Except each frame is actually projected three times, leading to a shutter speed of 72 frames per second. (In reality there are far more options today with IMAX and video tech, though.)

Even though there's only 24 images on the film per second, this triple exposure results in a smoother experience for the viewer. This is due to how critical flicker fusion works (a.k.a. persistence of vision). [1] (Though another reason for doing it is simply so that the film won't be burnt, since those xenon gas projection lamps run very hot.) See also beta movement and phi phenomenon. [2]

These physiological phenomena are of course very important to consider when making VR devices and games.

In order to create the effect mechanically in the film projector, each frame has to be stationary before the shutter is opened. If not, all you'd see is a blur. Thus, when the film is pulled forward, the shutter blocks the light from projecting the image onto the screen. In fact, during some half of the movie, people are actually sitting is pitch black darkness. Think about that next time you go to the movies! ;)

Please note that peripheral vision has a higher sensitivity to flicker than foveal vision. I'm unsure how interlacing affects that, though, if applickable. This effect might also be different on video systems where various forms of interlacing may or may not be used.

[1]: https://en.wikipedia.org/wiki/Flicker_fusion_threshold

[2]: https://en.wikipedia.org/wiki/Beta_movement

(Please excuse my lack of sourcing. Most of this is off the back of my head, and from books I am no longer in posission of... But the Wikipedia links should give you a good start.)


> Thus, when the film is pulled forward, the shutter blocks the light from projecting the image onto the screen.

Ironically, it sounds like a complement to saccades! Where saccades involve shutting off vision when your eye moves, this involves shutting off projection when the image moves.




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