I have always noticed that when I first glance at a watch/clock with a sweep second hand, it (the sweep second hand) at first appears to be frozen in time, as it were. Is this a recognized optical phenomenon, or my own peculiar illusion?
Bill (Chicago)
Well, television works because when you show a picture on the screen for a fraction of a second, your brain “fills in” the rest and assumes that there is a picture there even when it is blank.
Possibly when you glance at a watch for a fraction of a second, your brain “fills in” the fractions of a second that you were looking at nothing in particular and assumes that the second hand was in the same relative place for longer than it actually was?
I have noticed the phenomenon myself for digital clocks/watches with second hands. I look at it for what seems like more than a second but the second display is stationary all the time. I’m sure it is because I caught it at exactly the right time and my brain fills in a little bit before and after and assumes it has been stationary the whole time.
I is recognized. We have discussed it here before and I remember that a scientist devoted a study or two to it. I will see what I can find.
I think people are assuming that this is a phenomenon of perception of the clock being adjusted by the brain. The natural assumption for me is that your perception of time is slower when switching context - in fact it could possibly be a survival trait, you have more time to react to new stimulus that could prove dangerous.
Is that not because the second hand stops and goes? Having recently bought a wall clock with an advertised “sweep second hand”, I was bemused to see and hear that the hand jerks its way tickingly around the clock face. I had been expecting a smooth, quiet hand. (The clock brand is Equity, not Barnum, and the effect on my pocketbook is the same.)
Well, per online dictionaries, the sweep is like the path traveled – the hub to the edge – and per watchuseek’s thread response, post #9, “The reason standard quartz watches move in on second jumps is to minimize the current drain on the battery.” I welcome a Straight Dope response from a horologist, or from someone who is better than I at searching Cecil and General Questions.
It is a real effect, and it is NOT an “optical” illusion, strictly speaking.
Some time ago, the Canadian Broadcasting Corp. (CBC) Radio show “Quirks and Quarks” ran an episode that had a segment dealing with this. I can not remember the scientist’s name, but how he explained it was that it was caused by our brain function. So it is a neuralogical “illusion”, not an optical one.
What happens is that the part of the brain that “notices” duration takes time to “get into gear”, and so the second hand seems to hang for a bit while it catches up to the information coming in from the eye. Other parts of your brain “know” that the hand should be moving, and hence the discontinuity between what you see, and what you think you should be seeing. I don’t recall the exact part of the brain, but I think it was located in the left limbic lobe…
Regards
FML
I’d really appreciate a cite on this because it’d be fascinating for me to read. I’ve noticed this and many other similar effects myself a long time ago and they’ve always felt like it’s a particular aspect of changing context that makes some parts of my brain go into overdrive to allow for rapid response. I can’t wrap my mind around perceiving it as anything other than my brain working faster, not slower, than normal.
I guess an interesting test could be devised with a buzzer and a computer connected clock. In the test case, the subject does not see the clock when it is suddenly revealed, and if the # of seconds is divisble by 5(in one of the 12 marked positions) you push the buzzer before the hand moves. In the control test a person watches a clock on a computer monitor that displays random # of seconds every second, and pushes the buzzer before the clock switches. It’s not a very definitive test, by any means, but my hypothesis is that the test group will have a shorter average response time.
[nitpick]
This is true of film projection, in which there are moments of black screen between the frames. But the television image (at least on a CRT screen) is created by a constantly moving electron beam that traces out the picture the way you read a page of text: from left to right, line by line, from top to bottom. After the beam passes, the phosphors fade out until the beam comes back for the next frame. But the whole screen is not black between frames. On modern digital screens (LCD, DLP, plasma) all pixels are illuminated all the time, or nearly so.
[/nitpick]
In any case, whether in film or TV, this phenomenon is called “persistence of vision,” and is a function of the physical makeup of the eye. The chemicals produced in the retina that create the visual signal cannot be turned on and off more than about 20 times a second, so we can’t detect the flickering and so perceive a continuous moving image. (Edison, the Lumieres, and other early motion picture pioneers increased the frame rates of their projectors until they exceeded the eye’s ability to see individual frames.)
But persistence of vision is a physical, chemical process, quite different from whatever the brain is doing to create the effect the OP is talking about.
In one of Oliver Sacks’ books, he describes someone who had lost the ability to percieve motion. They would see the world as a series of still images.
It was a very frightening world that person lived in, this thread sounds like the normal version of what that person had abnormally.
This is a link to the original “Quirks and Quarks” episode, the article is the second one down the page - “Time Stands Still”
Regards
FML
I always thought “sweep” second hands were ones that swept in a continuous motion rather than ticking second by second. Not that that has much to do with the question…
I agree. However even the second hands on watches with mechanical movments do not move continuously. Their ‘steps’ are just not in whole seconds. The watch I’m currently wearing as a 37 jewel movement. At a glance it looks as if the second hand’s motion is continuous; but if one looks very carefully it can be seen that there’s still a small amount of ‘jerkiness’ to it. I’m not an expert, but a WAG would be that the second hand stops 16-24 times per second.