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.