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Olivia: Every now and then, you may have wondered how your pets or other animals experience time.  Like, does every day for Fido feel like two, and what about mosquitoes or house flies that only live for a week or a month?  We'll never be able to get inside another animal's head and feel what it's like for them to experience a day, but whether that day is a blip or an eternity probably has something to do with how they process sensory information. 

The leading idea suggests that with slow processing, time feels fast, and with fast processing, time feels slow, so maybe for your puppy, time really does seem different.  Given what we know from our own experiences, this hypothesis makes intuitive sense.  Baseball and tennis players, for instance, will often say that right before they swing their bat or racket, it's like the ball slows down.  There are a bunch of things that can distort time for humans, and psychologists spend a lot of well, time studying them, but at a basic level, biologists think that the broad strokes can be explained by good ol' evolution, and whether it's beneficial for a creature to have fast sensory processing or not.

Fast processing is great, but it's also metabolically expensive.  After all, you've gotta feed the brain, and it may or may not make sense to have super-sonic processing if you're a giant leatherback turtle.  That would be a lot of extra food.  About five years ago, a group of biologists in the UK and Ireland officially tested out these ideas, and they published their results in the journal Animal Behavior.  They hypothesized that body size and metabolism could predict how quickly an animal senses the passing of time.  To figure out how, they measured something called the critical flicker fusion frequency.  This is the speed at which a flashing light no longer appears to be flickering and just looks to be on, and it can give researchers a rough idea of something's visual processing speed.  In fact, it's the same principle behind movies, which really are better described by their old timey names, motion and moving pictures, because what they are is really a series of still images.  It's only when they're flashed quickly enough that we lose track and see movement.  

For humans, the flicker fusion frequency is about 60 times a second, but other animals have radically different measures.  Some see visual changes only once every 15 seconds, while others update things twice as quickly as us.  The team scoured the literature for flicker fusion frequencies for 34 vertebrates from all walks of life, including mammals, birds, reptiles, amphibians, and fishes, and they found that, generally speaking, their hypothesis was right: bigger animals with slower metabolisms had lower fusion frequencies, while smaller, high-metabolism creatures had higher values.  In other words, tiny amped-up chipmunks and pigeons are running and flying around seeing a lot of stuff every second, which makes time seem much slower than it does to us.  

Although this specific study didn't investigate insects, this could also explain why it's so hard to swat away a fly.  It's getting visual information so quickly, it's like your arm is moving at matrix level slo-mo.  Escape just isn't very hard.  Bulky turtles or chill eels, though, see far less, making time seem like warp speed.  Bigger animals can't move as quickly as their smaller-boned counterparts, anyway, so it makes sense that they don't have the ability to sense things on faster time scales.  After all, you shouldn't invest in costly things if you can't make use of them.

This relationship is a good rule of thumb, but it doesn't capture some special cases.  We know of some creatures, for example, that despite their tiny size, have slow visual processing systems.  The tiger beetle, for example, refreshes its view so rarely that it hunts in a disjointed stop/start pattern.  It sprints toward prey, only to abruptly stop so it can re-evaluate where it is in space.  It literally outruns its brain's ability to keep up.  So presumably, a day clicks by pretty fast.

Meanwhile, other animals have special ways of making sure they can devote extra energy to their visual systems, even if they're pretty big.  Predatory swordfish, for instance, have unusually warm eyes and brains, which scientists think allows the fish to be better hunters.  Then, there's the love spot, which isn't what it sounds like.  It's a special section of the eye in male flies that has super fast photoreceptors.  They're linked to speedier neurons for tracking down females for mating, and they suggest that time might pass at different speeds even within a single species. 

That might even be the case for us, too.  There's some evidence that, compared to adults, children experience time as moving more slowly, although it's definitely up for debate.  Still, one way or another, it seems like time isn't perceived the same way across the animal kingdom, because evolutionarily speaking, it doesn't need to be.  

Also, if you're still wondering about your pets, it turns out that cats aren't too far off from us.  They perceive time just a tad more quickly, and for dogs, time is probably about 30% slower, so not quite an extra day.

Thanks for watching this episode of SciShow, a Complexly production.  If you'd like to learn even more about animals and how they interact with the world around them, you can check out one of our sister programs, Animal Wonders, over at YouTube.com/AnimalWondersMontana.  

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