Scientists are getting closer to determining the serious implications of some seemingly mundane questions. Does your dog really know he was supposed to get his walk 30 minutes ago? And when your cat pops her tail and ignores you after you return from vacation, does she really know you were gone for two weeks instead of the usual eight hours?
In other words, does the family pet have a human-like memory system that allows it to travel back through time?
The answer to the first two questions is probably yes, but that doesn't mean Fido remembers when and where past events occurred in the same way that a human uses "episodic memory" to travel backward and forward in time. Much research has been devoted to the subject, and while it may seem trivial, it "goes to the heart of human uniqueness," according to psychologist William A. Roberts of the University of Western Ontario, Canada.
For several years now, Roberts has struggled with this fundamental question: Are animals stuck in time? Yes, in the sense that they lack "an ability to remember specific events in their past, what they were, where they happened, when they happened," he said in an interview.
Unlike humans, he added, other animals are not "mental time travelers."
Roberts is the author of a research paper in the journal Science that describes experiments he conducted with rats. He wanted to find out if rats could "remember when something happened in an absolute time dimension going into the past." In other words, could they place the memories in time, as to when it occurred, and where it occurred. That is the episodic memory that allows humans to travel through time, recalling when and where something happened. Can rats do that also?
This is a much easier question to answer for humans than it is for rats, or for cats and dogs. As psychologist Thomas R. Zentall of the University of Kentucky, Lexington, pointed out in a research paper, you can ask a human about past events and see if he or she has episodic memory, but you can't ask a rat and get a useful answer. Instead, you have to set up a maze consisting of a series of arms extending out from the center, and then watch the rat to see if it truly remembers when and where it found a juicy chunk of cheese.
Roberts did just that and found that rats could remember how long ago they found the cheese, and which arm of the maze it was on. If they had found the cheese at four-hour intervals, and were released after four hours, for example, they raced back to the same arm to see if the cheese was there. Thus they knew how much time had passed, and they could use it to their advantage.
"We found that the animals that could use how long ago, or how much time had gone by, were very good at the task [of returning to the same place in search of the cheese,]" Roberts said.
Other rats in the experiment, however, had a much more difficult assignment. They had found the cheese at a specific time of the day. If they were released at the same time the next day, would they use their memory of the preceding day to lead them to the cheese? No way. If all they had to work on was the time of day, they "seemed to be pretty much clueless," Roberts said. They didn't know which arm had produced the cheese at the same time yesterday.
"Humans can specify when an event occurred within a past temporal framework of hours, days, and years, but rats appear to remember only how much time has gone by since an important event occurred," Roberts' study concludes. Thus the rat's memory system is very different from a human's.
But doesn't this all just prove that rats can't tell time? No, Roberts said, because rats, like many other animals, are very good at telling time.
"Any pet owner will tell you that if you feed your dog or cat at a certain time of day the animal will start hounding the food bowl at the appropriate time of day," he added. They are very good at recognizing specific time intervals, like 30 seconds from the last time his ears were scratched, or three hours since the last walk, "but they can't remember time as a dimension that extends into the past."
That's because recognizing time as a abstract progression of events and memories is probably pretty new on this planet, even for humans.
"Early humanoids may not have been very sensitive to time," Roberts said. "It may be that this abstract dimension evolved as people had to keep track of time for different seasons of the year when crops were to be planted and so forth, and we eventually developed time technology. But I'm suggesting that animals don't use calendars and clocks and they are not sensitive to time as a dimension the way we are."
Some animals, however, have been pretty clever at hiding that. An earlier experiment found that scrub jays, members of the famously clever corvidae family of birds, could remember where and when they had discovered food. Thus some researchers concluded that the jays had human-like episodic memory of when and where something happened.
Now, Roberts suggests an alternative explanation.
"Instead of remembering when an event happened within a framework of past time, animals are keeping track of how much time has elapsed since caching or encountering a particular food item at a particular place and using elapsed time to indicate return to or avoidance of that location," he wrote in his report in Science.
They don't need this terribly abstract concept of time, and mental travel through it, to find their lunch, he suggests, so they are very different from you and me.
But that doesn't let the pet owner off the leash. The puppy still knows when you leave and when you are expected to return.
"There's no doubt that animals bond with people and become very dependent on them," Roberts said. "So I'm sure they probably do suffer emotionally when the owner leaves them for an extended period of time."
They may even know when you are long overdue, enjoying a vacation from the pooch, so go ahead, dial your answering system and let your pet hear your voice. Chances are, the pet will be counting the minutes, but not experiencing a mental journey through time, until your return.
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.