“Time stretches if you keep busy.” That is the title of a recent article on the New Scientist website that caught my attention, because it seems to contradict the common notion that time appears to pass faster when you’re having fun (which I tend to equate with keeping busy, for some reason). We would probably all agree that when we are bored, with nothing to do, time seems to drag on, so it surprised me that this should be the case when we keep busy, too.
The article describes research investigating how our brains measure time. This is not as trivial as it may sound; by itself, a brain is actually mostly helpless – it relies on the input from the senses and internal signals to gain information on our surroundings and the state of our body, which it then processes to produce an output – our perception of the world and responses to the stimuli we receive.
That processing often involves time as a factor (for example when we need to tell how fast something is moving). For that, however, the brain needs a standard clock it can use as a benchmark. The assumption has been that we have some kind of internal clock that keeps time for our brain, like a metronome for a musician. But we didn’t know if the brain uses any information from our surroundings to keep track of time as well. So, to quote New Scientist:
To test whether external stimuli might also play a role in our ability to process time, Misha Ahrens and Maneesh Sahani at University College London showed 20 subjects a video of either a randomly changing stimulus – statistically modelled on the way that things naturally change randomly in the world around us – or a static image, for a set period of time.
When asked to judge how much time had passed, the volunteers who had been shown the moving stimulus were significantly more accurate. The subjects were also shown the video at two different speeds and asked to rate the duration of each clip. They thought both clips lasted the same amount of time, even though the faster version was shorter (Current Biology, DOI: 10.1016/j.cub.2010.12.043).
This means that the brain perceives time differently when the input from the eyes is different, ie external stimuli do play a role. It seems that the brain has a certain expectation of the rate at which changes occur in the visual input, and our perception of time is calibrated against that standard. That doesn’t mean we do not have an internal clock. It just means that the brain makes use of additional information, when available, to fine-tune the reading on that internal clock.
It also doesn’t mean that time can’t fly when we are having fun…