https://digest.bps.org.uk/2021/12/21/watching-a-lecture-twice-at-double-speed-can-benefit-learning-better-than-watching-it-once-at-normal-speed/

a new paper in Applied Cognitive Psychology….

231 student participants to watch two YouTube videos (one on real estate appraisals and the other on the Roman Empire) at normal speed, 1.5x speed, 2x speed or 2.5x speed. They were told to watch the videos in full screen mode and not to pause them or take any notes. After each video, the students took comprehension tests, which were repeated a week later. The results were clear: the 1.5x and 2x groups did just as well on the tests as those who’d watched the videos at normal speed, both immediately afterwards and one week on. Only at 2.5x was learning impaired.

When the team surveyed a separate group of UCLA students, they found that a massive 85% usually watched pre-recorded lectures at faster than normal speed. However, 91% said they thought that normal speed or slightly faster (1.5x) would be better for learning than 2x or 2.5x. These new results certainly suggest that this isn’t right: double-time viewing was just as good as normal viewing.

While 2x viewing was fine for learning about the material in their studies — real estate appraisals and the Roman Empire — perhaps it might not work for more complex subject matter; again, only more research will tell.

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more on 2x in this IMS blog
https://blog.stcloudstate.edu/ims?s=2x