Any dog owner who has tried to sleep in on the weekend knows the answer to this question. Pet dogs (and plenty of cats) sure seem to have some sort of internal clock that lets them know when it's time to eat, sleep and certainly when it's time for you to get out of bed in the morning.
Most dog owners will tell you their pets always seem to know when it's mealtime, when people are expected to leave and come home and when it's time to go to sleep at night.
Obviously, dogs can't read clocks or count minutes, so how do they have a concept of time?
Clock-like neurons in the brain
A new study from Northwestern University has found evidence that animals judge time. Researchers examined the brain's medial entorhinal cortex (MEC), which is associated with memory and navigation. They found a previously undiscovered set of neurons that flip on like a clock whenever an animal is in waiting mode.
"Does your dog know that it took you twice as long to get its food as it took yesterday? There wasn't a good answer for that before," said study leader Daniel Dombeck, in a statement. "This is one of the most convincing experiments to show that animals really do have an explicit representation of time in their brains when they are challenged to measure a time interval."
For the study, which was published in the journal Nature Neuroscience, researchers set up a treadmill with mice in a virtual reality environment. The mice learned to run down a hallway in the virtual reality scene to a doorway. After about six seconds, the door opens and the mouse can go down the hallway and get a reward.
After several training sessions, the researchers made the door invisible in the virtual reality scene, yet the mouse still waited six seconds in the same spot before racing down the track to collect its reward.
"The important point here is that the mouse doesn't know when the door is open or closed because it's invisible," said James Heys, a postdoctoral fellow and the paper's first author. "The only way he can solve this task efficiently is by using his brain's internal sense of time."
Sense of smell
Alexandra Horowitz, author of "Being a Dog: Following the Dog into a World of Smell," says dogs detect time with their noses.
"Smells tell time, in other words, strong odor is probably newer odor, laid down more recently. A weaker odor is something that was left in the past. So being able to detect the concentration of a smell, they're really seeing not only what it is, but how long ago it was left," she tells NPR.
"Smells in a room change as the day goes on. Hot air rises, and it usually rises in currents along the walls and will rise to the ceiling and go kind of to the center of the room and drop. If we were able to visualize the movement of air through the day, what we're really visualizing is the movement of odor through the day. In the mid-afternoon you might feel tangibly on your skin, or see through the light in the window, that it's afternoon and the sun is half-way in the middle of the sky. The dog, I think, can smell that through the movement of that air through the room."
Have you ever noticed that you dog seems to be expecting you at the door when you come home from work?
Your personal scent starts to dissipate the longer you are away and there's a chance that your pet keeps track of how much your smell fades. Watch this experiment as one dog, Jazz, is thrown off expecting his owner's arrival all with the help of some particularly smelly clothes.