Science Questions

Why does the first tick take so long?

Tue, 12th Jan 2016

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Dan Wheeler asked:

When you first look at a clock with a second hand, why does that first second always take so long to tick?


Chris Smith and Ginny Smith tried their hand at this question...An old style alarm clock

Chris - And it's absolutely true isn't it.  You must have all noticed this and I think it comes down to what you're saying basically which is, that the processing delay through your visual system is at least 150-250 milliseconds.  In other words, a pretty high fraction - a fifth of a second goes by between the time that actually something is presented to you and you actually being able to process that information through your visual areas of your brain.  And it may may take up to a third of a second before your consciousness then integrates that and puts that visual stimulus into your conscious experience.  So when you're looking at the clock, there's going to be a delay when you first look at the clock while your visual system compares what is the clock looking like, what did it look like - oh look it's now moved, and then it becomes a streamline process.

Ginny - The other time where you see that  delay is if you've ever done that thing where you've seen something out of the corner of your eye and thought that it was a spider or a snake and had that moment of panic, and then noticed that actually it's the garden hose or it's some, you know, fluff on the side.  You get that moment of panic because you're unconscious parts, the subconscious parts of your brain register the threat and then the conscious parts get the information from your visual system and go - oh no, hang on, it's just a garden hose, calm down.  So then you can really see that difference between how fast your conscious and unconscious processing is.


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It doesn't, just tested. JeepKeen, Sat, 5th Mar 2016

Bored chemist, Sat, 5th Mar 2016

I have perceived this delay with analogue clock second-hand & with digital clock displays which blink every second ... RD, Sat, 5th Mar 2016

Probably some sort of optical illusion. An example that's sort of the same is the rising moon. It looks larger when near the horizon than when it's overhead. This is because our brain expects things to be a certain way. If a hot air balloon was over your head, it would tend to look larger, then get smaller as it approached the horizon. The brain tends to interpret the moon as something that would behave the same way. Your brain thinks the moon should get smaller as it heads toward the horizon, so when it stays the same size, your brain compensates by telling you it's larger than it actually is. I suspect your clock is the same. When you look at it, you expect the second hand to be moving, so when it isn't, your brain exaggerates the effect. Craig W. Thomson, Sat, 5th Mar 2016

A better analogy is when a YouTube video slows or freezes because of a momentary sub-normal data delivery rate. RD, Sat, 5th Mar 2016

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