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2012-08-29 09:36:34
Have you ever stared at a second hand on a clock and thought that time seemed
to stand still for a moment? It s not just you.
Sometimes, when I look at a clock time seems to stand still. Maybe you've
noticed this to your bemusement or horror as well. You'll be in the middle of
something, and flick your eyes up to an analogue clock on the wall to see what
the time is. The second hand of the clock seems to hang in space, as if you've
just caught the clock in a moment of laziness. After this pause, time seems to
restart and the clock ticks on as normal.
It gives us the disconcerting idea that even something as undeniable as time
can be a bit less reliable than we think.
This happened to me for years, but I never spoke about it. Secretly I thought
it was either evidence of my special insight to reality, or final proof that I
was a little unhinged (or both). But then I found out that it s a normal
experience. Psychologists even have a name for it - they call it the stopped
clock illusion . Thanks psychologists, you really nailed that one.
An ingenious experiment from a team at University College London recreated the
experience in the lab and managed to connect the experience of the stopped
clock to the action of the person experiencing it. They asked volunteers to
look away and then suddenly shift their gaze to a digital counter. When the
subjects tried to judge how long they had been looking at the digit that first
appeared, they systematically assumed it had been on for longer than it had.
Filling gaps
Moving our eyes from one point to another is so quick and automatic that most
of us probably don't even think about what we are doing. But when you move your
eyes rapidly there is a momentary break in visual experience. You can get a
feel for this now by stretching your arms out and moving your eyes between your
two index fingers. (If you are reading this in a public place, feel free to
pretend you are having a good stretch.) As you flick your eyes from left to
right you should be able to detect an almost imperceptibly brief flash of
darkness as input from your eyes is cut off.
It is this interruption in consciousness that leads to the illusion of the
stopped clock. The theory is that our brains attempt to build a seamless story
about the world from the ongoing input of our senses. Rapid eye movements
create a break in information, which needs to be covered up. Always keen to
hide its tracks, the brain fills in this gap with whatever comes after the
break.
Normally this subterfuge is undetectable, but if you happen to move your eyes
to something that is moving with precise regularity like a clock you will
spot this pause in the form of an extra long second . Fitting with this
theory, the UCL team also showed that longer eye-movements lead to longer
pauses in the stopped clock.
It doesn't have to be an eye movement that generates the stopped clock all
that appears to be important is that you shift your attention. (Although moving
our eyes is the most obvious way we shift our attention, I'm guessing that the
inner eye has gaps in processing in the same way our outer eyes do, and these
are what cause the stopped clock illusion.) This accounts for a sister illusion
we experience with our hearing the so-called dead phone illusion , which is
when you pick up an old-fashioned phone and catch an initial pause between the
dial tone that seems to last longer than the others.
These, and other illusions show that something as basic as the experience of
time passing is constructed by our brains and that this is based on what we
experience and what seems the most likely explanation for those experiences,
rather than some reliable internal signal. Like with everything else, what we
experience is our brain's best guess about the world. We don't ever get to know
time directly. In this sense we are all time travellers.