Why does the seconds hand appear to move backwards when you first glance at a clock?
In: Biology
This is known as the “stopped clock illusion” and most people see it as a long pause of the second hand rather than it actually moving backwards (but some do see it moving backwards). It comes from the way our brain edits out blurry input from moving eyeballs. When you first look at a clock or watch, your eyeballs moved to get the clock or watch in frame, and the movement produces a blurry image for a split second. Once your eyes stop moving, there’s a clear image for your brain to process and it literally overwrites the blurry image with the clear image. But now the clear image is “what you see” for a few milliseconds longer than you really saw it, so fast moving things (like a second hand) appear stopped or slowed (and in some cases, moving backward) for very brief time – basically the time of the blurry image is replaced with the non-blurry image. We don’t notice this without some fast moving and expected thing in the image (like a second hand).
Latest Answers