As a quick recap, there are different kinds of memory. Semantic memory refers to knowledge and information; an example of a semantic memory for me is knowing the different kinds of memory. Episodic memory refers to events, things that have happened in your life; for me, an example would be remembering that I've written posts about memory before. The two are obviously connected, and influence each other. A memory of an event (episodic memory) may teach you a lesson or rule for living (semantic memory). And remembering that I've written posts about memory before (episodic memory) includes remembering the content of those posts (semantic memory).
The researchers examined episodic memory in 17 dogs using an unexpected recall task. If you know you're going to be expected to recall something, you "memorize" it, meaning committing it to semantic memory (also referred to as explicit encoding - you stored it because you know you'll need it later). But if you don't expect that you'll have to recall the information, when you are suddenly asked to recall it, you'll draw on your episodic memory (also referred to as incidental encoding - you stored it even though you didn't expect to need it). They tested this same phenomenon in dogs using a "Do As I Do" task:
Dogs were first trained to imitate human actions on command. Next, they were trained to perform a simple training exercise (lying down), irrespective of the previously demonstrated action. This way, we substituted their expectation to be required to imitate with the expectation to be required to lie down. We then tested whether dogs recalled the demonstrated actions by unexpectedly giving them the command to imitate, instead of lying down.
They found that dogs were able to imitate even when the command was unexpected, though their success rate decreased with longer recall periods (such as asking a dog to remember something from an hour ago - this is a test of memory decay, the loss of a memory as time since the event increases). So they were less able to imitate after a 1 hour delay, but some still could imitate.
Dogs may not be able to hold memories as long as humans can, but these results suggest that dogs can hold episodic memories: "To our knowledge, this is the first time that a non-human species shows evidence of being able to recall complex events (i.e., others’ actions) without motor practicing on them during the retention interval—thus relying on a mental representation of the action that has been formed during incidental encoding, as assessed by an unexpected test."
"Okay," you say, "my dog can remember events. So what?" George Dvorsky, over at Gizmodo, interviewed the study researchers, where they discuss that episodic memory is connected to self-awareness:
As noted, episodic memory has been linked to self-awareness, which is the ability to see oneself as an entity that’s separate and different from others. “So far no test has been successfully applied to study self-awareness in dogs,” Fugazza told Gizmodo. “We believe that our study brought us one step closer to be able to address this question.”