Research suggests perception of time is linked to size, explaining why insects find it easy to avoid being swatted

This article is more than 7 years old

This article is more than 7 years old

Flies avoid being swatted in just the same way Keanu Reeves dodges flying bullets in the movie The Matrix – by watching time pass slowly.

To the insect, that rolled-up newspaper moving at lightning speed might as well be inching through thick treacle.

Like Reeves standing back and side-stepping slo-mo bullets, the fly has ample time to escape. And it is not alone in its ability to perceive time differently from us. Research suggests that across a wide range of species, time perception is directly related to size.

Generally the smaller an animal is, and the faster its metabolic rate, the slower time passes.

The evidence comes from research into the ability of animals to detect separate flashes of fast-flickering light.

"Critical flicker fusion frequency" – the point at which the flashes seem to merge together, so that a light source appears constant – provides an indication of time perception. Comparing studies of the phenomenon in different animals revealed the link with size.

"A lot of researchers have looked at this in different animals by measuring their perception of flickering light," said Dr Andrew Jackson, from Trinity College Dublin in the Republic of Ireland. "Some can perceive quite a fast flicker and others much slower, so that a flickering light looks like a blur.

"Interestingly, there's a large difference between big and small species. Animals smaller than us see the world in slo-mo. It seems to be almost a fact of life. Our focus was on vertebrates, but if you look at flies, they can perceive light flickering up to four times faster than we can. You can imagine a fly literally seeing everything in slow motion."

The effect may also account for the way time seems to speed up as we get older, said Jackson, who led the research. He was inspired to conduct the study after noticing the way small children always seem to be in such a hurry.

"It's tempting to think that for children time moves more slowly than it does for grownups, and there is some evidence that it might," he said.

"People have shown in humans that flicker fusion frequency is related to a person's subjective perception of time, and it changes with age. It's certainly faster in children."

TV, computer and cinema screens all flicker but provide the illusion of constant images because of the high frequencies at which they operate.

But dog owners may be surprised to learn that their pets can see TV flickers, said Jackson. Their visual system has a refresh rate higher than that of the TV screen.

The animals studied covered more than 30 species, including rodents, eels, lizards, chickens, pigeons, dogs, cats and leatherback turtles.

The latter are big creatures with a slow metabolic rate, for whom time passes relatively rapidly.

Smaller, more agile creatures had the most refined ability to perceive information in a unit of time, said the researchers writing in the journal Animal Behaviour. In other words, they were able to see more flickers of light per second.

Time perception is just another aspect of evolution and survival, the scientists believe.

"Our results lend support to the importance of time perception in animals where the ability to perceive time on very small scales may be the difference between life and death for fast-moving organisms," said co-author Kevin Healy, a PhD student at the school of natural sciences at Trinity College, Dublin.

Prof Graeme Ruxton, from the University of St Andrews in Scotland, who also took part in the research, said: "Having eyes that send updates to the brain at much higher frequencies than our eyes do is of no value if the brain cannot process that information equally quickly. Hence, this work highlights the impressive capabilities of even the smallest animal brains.

"Flies might not be deep thinkers, but they can make good decisions very quickly."

Some animals may exploit differences in time perception to their advantage, according to Dr Luke McNally, another member of the team from the University of Edinburgh.

"For example, many species use flashing lights as signals, such as fireflies and many deep-sea animals," he said. "Larger and slower predator species may not be able to decode these signals if their visual system isn't fast enough, giving the signallers a secret channel of communication."