Slow-motion world for small animals

Starling feeding on apples Starlings were found to have very fast visual systems, a result of observing the world very slowly

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Smaller animals tend to perceive time as if it is passing in slow motion, a new study has shown.

This means that they can observe movement on a finer timescale than bigger creatures, allowing them to escape from larger predators.

Insects and small birds, for example, can see more information in one second than a larger animal such as an elephant.

The work is published in the journal Animal Behaviour.

"The ability to perceive time on very small scales may be the difference between life and death for fast-moving organisms such as predators and their prey," said lead author Kevin Healy, at Trinity College Dublin (TCD), Ireland.

The reverse was found in bigger animals, which may miss things that smaller creatures can rapidly spot.

Speedy creatures

golden mantled ground squirrel,
  • Animals with the fastest visual systems in the database included golden mantled ground squirrels, starlings and pigeons
  • The starling lives in large groups and forms massive swirling flocks which might be related to its need to keep track of where its mates are and avoid collisions
  • One species of tiger beetle runs faster than its eyes can keep up, according to the team. It essentially becomes blind so needs to stop periodically to re-evaluate its prey's position
Speedy goalkeeper

In humans, too, there is variation among individuals. Athletes, for example, can often process visual information more quickly. An experienced goalkeeper would therefore be quicker than others in observing where a ball comes from.

The speed at which humans absorb visual information is also age-related, said Andrew Jackson, a co-author of the work at TCD.

"Younger people can react more quickly than older people, and this ability falls off further with increasing age."

The team looked at the variation of time perception across a variety of animals. They gathered datasets from other teams who had used a technique called critical flicker fusion frequency, which measures the speed at which the eye can process light.

Plotting these results on a graph revealed a pattern that showed a strong relationship between body size and how quick the eye could respond to changing visual information such as a flashing light.

"From a human perspective, our ability to process visual information limits our ability to drive cars or fly planes any faster than we currently do in Formula 1, where these guys are pushing the limits of what is humanly possible," Dr Jackson told BBC News.

"Therefore, to go any quicker would require either computer assistance, or enhancement of our visual system, either through drugs or ultimately implants."

Confused woodlice

The current study focused on vertebrates, but the team also found that several fly species have eyes that react to stimulus more than four times quicker than the human eye.

Sluggish creatures

The leatherback turtle
  • The common European eel, the leatherback turtle, and the blacknose shark had the slowest visual systems
  • Although the eel and blacknose shark are relatively small, they have slow metabolisms which explains their slow visual systems
  • The leatherback is a huge turtle that feeds primarily on slow moving jellyfish and has a very slow metabolism itself, so doesn't need to invest in high visual processing equipment

But some deep-sea isopods (a type of marine woodlouse) have the slowest recorded reaction of all, and can only see a light turning off and on four times per second "before they get confused and see it as being constantly on", Dr Jackson explained.

"We are beginning to understand that there is a whole world of detail out there that only some animals can perceive and it's fascinating to think of how they might perceive the world differently to us," he added.

Graeme Ruxton, of the University of St Andrews, Scotland, another co-author, 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."

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