Though our perception of time can be stunningly precise — given a beat to keep, professional drummers are accurate within milliseconds — it can also be curiously plastic. Some moments seem to last longer than others, and scientists don’t know why.

Unlike our other senses, our perception of time has no defined location in our brain, making it difficult to understand and study. But now researchers have found hints that our sense of time stems from specialized units in our brain, channels of neurons tuned to signals of certain time lengths.

“We know keeping track of time is incredibly important, it allows us to coordinate movements, interpret body language,” said optometrist James Heron of the University of Bradford in the UK, lead author of the study in Proceedings of the Royal Society B, Aug. 10. “We know the brain does this routinely and accurately, but we’re not sure how. Our evidence strongly suggests the presence of neural units in the brain that are tuned to different durations.”

Researchers who study the brain’s perception of time have previously proposed several ways our mental clock might work. It could be like a metronome, ticking at a regular rate, allowing us to keep track of time by unconsciously counting the clicks. Or it may judge time based on the amount of energy needed to process a signal. The more attention we give to something, the longer the processing seems to take.

Heron and his colleagues believe our mental chronometer runs, at least partially, on neuron channels that respond to a specific “frequency of time.” The new experiment exposed people to one hundred beeps or flashes of a certain duration, which adapted the people to signals of that length.

They then tested the participants’ time judgment by giving them a beep and a flash and asking which had lasted longer. What they found was flashes and beeps that were close in duration to the signals the people had been adapted to were consistently judged to be significantly longer than they really were.

“If I present you with lots of flashes that last 150 milliseconds, then a 300 doesn’t feel like 300, it feels more like 400,” Heron said.

The closer the signals were to the duration they were adapted to, the further off peoples’ guesses were.

“The channel-based system seems the best explanation for this,” Heron said. “It was as if we fatigued the channels tuned to that duration, and the channels near it, but the channels further away were still fresh.”

While not changing our understanding of psychology, Heron’s conclusions give an intriguing “peek at the machinery under the hood,” said neuroscientist David Eagleman, director of the Laboratory for Perception and Action at Baylor College of Medicine.

“What we know about vision and hearing suggests that different populations [of neurons] in the brain are tuned to different properties,” said Eagleman, author of Incognito, “so the idea that there may be populations of neurons tuned to different durations is plausible and in line with previous electrophysiology data.”

The workings of the brain are far from simple, however, and the channel-based model doesn’t explain why, for example, time seems to pass more slowly when we are in a life threatening situation like falling off a roof or a car crash.

“There is a lot going on in the brain,” Eagleman said. “You’re not just passively tracking the river of time. You’re actively constructing it.”

Image: Alex Lomix/Flickr.

Citation: “Duration channels mediate human time perception.” By James Heron, Craig Aaen-Stockdale, John Hotchkiss, Neil Roach, Paul McGraw and David Whitaker. Proceedings of the Royal Society B. August 10, 2011.