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See Inside Scientific American Mind Volume 25, Issue 4

Small Animals Live in a Slow-Motion World

Time seems to pass more slowly for lighter animals with faster metabolisms


TIME FLIES (BUT NOT IF YOU'RE A FLY) To a fly, an incoming swat appears to move in slow motion (as many would-be bug killers have suspected all along). That's because flies process about four times more visual information per second than humans do—they see 250 frames per second to our 60.


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One “dog year” supposedly equals seven human years. But does one year feel like seven years to a dog? Evidence suggests that distinct species do indeed experience passing time on different scales. A recent study in Animal Behavior reveals that body mass and metabolic rate determine how animals of different species perceive time.

Time perception depends on how rapidly an animal's nervous system processes sensory information. To test this ability, researchers show animals a rapidly flashing light. If the light flashes quickly enough, animals (and humans) perceive it as a solid, unblinking light. The animal's behavior or its brain activity, as measured by electrodes, reveals the highest frequency at which each species perceives the light as flashing. Animals that can detect the blinking at higher frequencies are perceiving time at a finer resolution. In other words, movements and events will appear to unfold more slowly to them—think slow-motion bullet dodging in an action movie.

The scientists who ran the new study gathered data from previous experiments on the rate at which visual information is processed in 34 vertebrates, including lizards, birds, fish and mammals. The scientists hypothesized that the ability to detect incoming sights at a high rate would be advantageous for animals that must perform the equivalent of bullet dodging—responding to visual stimuli very quickly to catch elusive prey or escape predators, for instance. These animals tend to be lighter and have faster metabolisms. The data bore out the hypothesis: species that perceived time at the finest resolutions tended to be smaller and have faster metabolisms.

These findings show that differences in how a mouse and an elephant sense time are not arbitrary but rather are finely tuned by interactions with their surroundings. A link between time perception, body structure and physiology suggests that different nervous systems have developed to balance pressures from the natural environment with energy conservation. Rapid perception might be essential for a hawk but would waste a whale's precious energy. As for Fido, a year really does seem longer to him than it does to you, but probably not by a factor of seven. Dogs can take in visual information at least 25 percent faster than humans—just enough to make a television show look like a series of flickering images.

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