Dogs remember things, as any dog owner can tell you. Whether it's knowing that the sound of food hitting the bowl means mealtime or recalling that the jingle of the leash means walk time, man's best friend consistently illustrates his ability to recount the meaning of specific cues. Now, new research shows that canines could also have a more complex form of memory that few nonhuman animals have been shown to possess—one that could even point to a sense of self-awareness.
There are two forms of "explicit memory," which is the kind of memory you use when intentionally recalling a piece of information. The first is semantic memory, which you use to recall information you’ve consciously learned or memorized. The second is episodic memory, which you use to remember everyday experiences and events that your mind encodes without conscious memorization. While you might use semantic memory to recount vocabulary words for a Spanish test, you’d use episodic memory when your friend asks you how your trip to the grocery store went yesterday.
Semantic memory is fairly common in the animal kingdom; chimpanzees can use it to memorize words and dogs can use it to associate commands with the actions they need to perform. But until recently, episodic memory has been considered “uniquely human.” Endel Tulving, the University of Toronto psychologist who first defined semantic and episodic memory in 1972, believed that episodic memory evolved only recently and only in humans. However, new research in the past few years has suggested that a few non-human animals such as chimpanzees, orangutans and bottlenose dolphins may also possess this form of memory.
Episodic memory has been associated with self-awareness: The theory is that, to recall these kinds of memories, you have to be able to imagine yourself in past events. “Many animals—mammals such as mice, squirrels, dogs, elephants, and chimpanzees, as well as most if not all birds—have excellent ‘semantic’ memory,” Tulving writes on his faculty webpage. “That is, they are capable of conscious learning of facts about the world. However, there exists no evidence that they can mentally travel in time in the same was as humans do, to remember the past and to plan for the future.”
When it comes to humans, testing for episodic memory is relatively straightforward; just ask them to recall something they didn't expect to be asked about. For animals, a little more creativity is required, says Etövös Loránd University animal psychologist Claudia Fugazza. Fugazza is the lead author of the first study of its kind on episodic memory in dogs, published last week in the journal Current Biology, which suggests that our canine companions may have more advanced memories than we thought.
To get around the fact that a dog can't tell you about its memories, Fugazza and her team decided to use distraction as a way of forcing dogs to rely on their episodic memory by making them recall an unexpected command. For the study, the researchers guided 17 dog owners as they trained their dogs to imitate them while they performed six different actions involving three different objects: a bucket, umbrella and chair. These "Do As I Do" commands were designed to create an expectation for the dogs: After their owners demonstrated an action, they were expected to follow suit.
The owners then distracted the dogs from that expectation by training them instead to simply lie down on a blue carpet after their owners demonstrated any of the same actions involving the same objects. Now, the dogs wouldn't need to remember which action their owners did; they just needed to lie down afterwards. Then came the key test of the dogs' episodic memory: While the dogs stood on the blue carpet that had been used during the lie down training, their owners demonstrated an action and waited for their dogs to lie down as they expected. They then suddenly gave the command to imitate them.
Could the dogs remember the action to imitate even while they were expected to just lie down after doing it?
Immediately after the demonstration, researchers found, most of the dogs were able to correctly remember which action to imitate. Even after an hour delay from the demonstration, several dogs could still remember which action to imitate.
For Fugazza, these results showed the unexpected potential for dogs to have a more complex memory than previously thought. But the study also suggests that dogs might make good subjects for future studies in animal psychology, in addition to more traditional lab animals like apes, rats and birds, she says. "We think that dogs are a very good model for studying [animal cognition]," Fugazza says. She points to "their advantage of living and having evolved in a human environment,” which means they are easier to train and work with than other study subjects.
However, that familiarity could also cause problems, warns Victoria Templer, a neuroscientist at Providence College in Rhode Island who wasn't involved in this study. Because dogs have evolved to respond so well to humans, she said, scientists would have to work hard to avoid the so-called "Clever Hans effect," in which humans can unknowingly prompt animals for an answer in experiments. For this reason, Templer said she likely would never work with dogs.
Nevertheless, she says she considers the design and results of Fugazza's study to be well-done, and she hopes to see more work like it in this field. "It’s one brick in the wall—we need other bricks in the wall to be able to say [for certain] that dogs have episodic memory," says Templer. So maybe don’t ask Fido how his trip to the grocery store went just yet.