LEILA FADEL, HOST:
All this month, NPR's looking into the science of time - how we perceive time and how that perception shapes our world and culture. But NPR's global health correspondent Michaeleen Doucleff had another question on her mind - how do dogs measure time?
MICHAELEEN DOUCLEFF, BYLINE: For years, when I visited my husband's family during the holidays, they would tell me the same story over and over.
You know the story, right, Matt?
MATT: Of course, yes.
DOUCLEFF: That's my husband Matt. And the story was about the family's dog.
MATT: Donut.
DOUCLEFF: And what type of dog was Donut?
MATT: She was a hound mix. You know, we knew that she was a hound because she likes to roam.
DOUCLEFF: Matt had Donut all through his childhood, from elementary school through high school.
So during the day, Donut spent most of the time inside, right?
MATT: Yeah, sleeping.
DOUCLEFF: But then, every school day, Donut would do something uncanny - at exactly the same time, right before the school bus brought Matt home.
MATT: Well, she would go to the back porch and sit down and wait for my brother and I to walk home and then greet us when we came home.
DOUCLEFF: So she was kind of like a canine alarm clock?
MATT: Yeah, she was always punctual and never early and never late.
DOUCLEFF: And for years I've wondered, how did Donut do it? How did she tell time?
ALEXANDRA HOROWITZ: I'm not at all surprised that Donut would be able to predict the arrival of the school bus.
DOUCLEFF: That's Alexandra Horowitz at Columbia University. She studies canine cognition. She says dogs, like people, use many clues to tell time. They listen to their bodies' physiological signs, such as a growing rumble in their tummies. They notice the amount of light shining into a room.
HOROWITZ: We all notice, oh, it's getting a little bit dark.
DOUCLEFF: But Horowitz says Donut is likely using something else to calculate when the bus is going to arrive. And that's...
HOROWITZ: Olfaction.
DOUCLEFF: ...Her nose.
HOROWITZ: Dogs are living in basically an olfactory world. And they're probably able to track time through smell.
DOUCLEFF: Now, when I first heard this, I was incredulous. How do dogs smell something like time? But then Horowitz explained it to me. And it starts with us humans.
HOROWITZ: Humans smell. You know, we stink, right? You know, we might not want to think we do, even the very clean among us.
DOUCLEFF: And we spread that odor all over our room.
HOROWITZ: We leave our odor signature everywhere.
DOUCLEFF: So you can imagine, back in the '90s, when Matt was getting ready for school in the morning, his house filled with his unique scents, from his stinky socks to the new shampoo he used, and those smells hung around even after he went to school.
HOROWITZ: If we've been in that space, we've left some of us there.
DOUCLEFF: But as time went by, the scent of Matt faded from the room.
HOROWITZ: The odors deteriorate. The smell gets less strong.
DOUCLEFF: Then at 3 p.m. each day, when the bus was on its way, the smell of Matt probably reached about the same level every day, and Donut would have noticed that level.
HOROWITZ: Given that things like school buses arrive at about the same time every day, pretty quickly they would associate a weaker odor with the person being about to return.
DOUCLEFF: They're, like, really, like, smelling time in some sense, right?
HOROWITZ: Yeah.
DOUCLEFF: Versus we're, like, seeing it and feeling it; they're, like, really smelling time go by.
HOROWITZ: We have to imagine that they might experience faces and recognize things and have memories, even in smell.
DOUCLEFF: Now, Horowitz is quick to point out that nobody has ever tested this hypothesis scientifically. But other researchers agree that Donut was likely using odors to predict the time of Matt's arrival. Lucia Lazarowski studies canine olfaction at Auburn University. She says dogs trained to track down missing people also smell time, and that's because as they follow a trail in space, they are sampling changes in the plume of scent.
LUCIA LAZAROWSKI: Tracking and trailing dogs are probably using the intensity of odors to determine the direction of a track or a trail.
DOUCLEFF: And so even when dogs are keeping track of physical space, they're also tracking time. And so for dogs, space and time are woven together, which, if you think about it, is reminiscent of the way scientists think about space and time. Who knew that while Matt was in elementary school working on multiplication, Donut had already mastered some fundamentals of physics.
Michaeleen Doucleff, NPR News.
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