Ruby flew down the hall, careened around the corner, and stopped just briefly to jump on me before charging off again. His pointy ears and tail bobbed and wagged in rhythm as he ran laps around the house. I had just come through the door on my first trip home from college and it was the best welcome-home I could ask for. Ruby’s exuberance over seeing me again, after our months apart, is a favorite memory from my college days.
Remembering my reunion with Ruby is an example of an episodic memory – recalling an experience. Such autobiographical memories – tied to specific places, times, and emotions – are integral to our lives as humans. There are other types of memory, for example, your phone number or each State’s capital city are semantic memories – memories for facts that build over time. But, as perfectly described in the lyrics of Bob Dylan’s Precious Memories, episodic memories are the ones that “flood the soul.”
The question for researchers in a recent study published in Current Biology is whether other animals besides humans share the ability for episodic-like memory. Could Ruby encode and recall memories of our experiences together something like I do? The first task for Claudia Fugazza and her colleagues was to design a memory test that would target episodic memory by ruling out reliance on learning, which would instead tap into semantic memory. Memory researchers agree that a crucial aspect of episodic memory is that memories are saved without the knowledge that they have to be remembered in the future. So, any test of episodic memory has to be unexpected.
For their study, the research group in Budapest, Hungary, enlisted the help of 17 pet dogs. Dogs are a particularly well-suited species to test the scope and evolution of cognitive abilities because they happily work with humans. Indeed, the dogs in this study were energetic participants who were all easily were trained to imitate a simple action, such as looking into a bucket or touching an umbrella, with the command “do it.” Previous research had already established dogs could remember such actions after a delay, so to insure a test of episodic memory specifically, researchers had to make sure that the dogs wouldn’t expect to imitate the demonstrated actions. The solution was to provide an alternative expectation. Now, immediately after watching their owners perform a series of actions the dogs were given the command ‘lie down’.
Because replacing dogs’ expectation to imitate with lying down was so important for the memory test, which had to be unexpected, the researchers tried to verify dogs’ new expectation to lie down in two ways. First, they received training until they would reliably lie down immediately after observing the actions, one indication they were indeed expecting the “lie down” command to follow. A second suggestion that dogs were indeed expecting a lie down request was if they acted surprised when they didn’t. Like humans and other animals, when dogs see something unexpected they register their surprise by looking at it longer.
Next came the unexpected – “do it” – the episodic memory test. Instead of the now expected “lie down”, one minute after dogs saw the last action they instead got the command to imitate. First, they did seem surprised, looking longer at their owners than previously. Then, nose to umbrella, paw on the chair… the majority of the dogs imitated their owner’s action. To see if they would still remember the action after a longer delay the dogs left the testing area for an hour before coming back for a second imitation request. Again, many dogs successfully imitated the action they had seen, though fewer then after the one-minute test or compared with a previous study where dogs were expecting to imitate. These results further support the idea that dogs were probably using episodic memory, which for people also fades more quickly than other types of long-term memory.
These results, one of a handful suggesting episodic-like memory in a non-human species, add to our growing knowledge of the richness of other animals’ mental lives. The dog cognition lab in Budapest is one of many around the world; pups in Connecticut can go participate at Yale University and dogs in North Carolina can help out at Duke University – all striving to help us understand how dogs, and humans too, think about and process the world. Dogs have been our partners for centuries. They share our homes and our work, and now we know they might share some of the rich memories of our lives together.