Why does the seconds hand appear to move backwards when you first glance at a clock?


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).

When your eyeball moves it will only capture a blur of motion. You do not see this because there is a mechanism in your brain which turns you blind while the eye is moving and also when you blink. However you do not see blackness or anything else, you just do not see anything. So when you try to remember the position of the seconds hand half a second ago you remember that you looked at the clock and you must have been looking at the clock at that time and seen the position of the seconds hand. But you do not actually remember what it was. This is fine though because your brain is constantly purging unimportant memories so you must be able to figure out why the memory was purged. Most people report seeing the seconds hand stay still because they would have seen the seconds hand move and remember it so it could not have moved and therefore must have been standing still for a bit. But some people instinctively know that the seconds hand moves every second so it must have moved but you do not remember it being in the previous position so it can not have moved forwards and therefore it must have moved backwards. The brain does not realize that the memory of the seconds hand moving is not the memory that is purged but rather it is the fact that you went blind for a split second, something which happens far more often, is the memory that is purged. And your brain does these things all the time and will rather rely on deductive reasoning rather then having to remember things.

It is the “stopped clock illusion & is a result of what is known as a “Saccade”, or being “saccadic”…
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