What kind of memory do dogs possess? I got interested in this question when I noticed that if my dog sees a cat under a particular bush, no matter how infrequently we pass by that bush, he always checks to see if the cat is there. I also noticed that once a postal carrier gave him a treat, he associated all mail carriers with treats - and quickly learned that not all carriers carry dog treats. Nonetheless, he still works hard to get the attention of all carriers just in case because he has been rewarded on the most powerful schedule of reinforcement - an intermittent one. But, that's another topic to be covered at some other time.
So back to a dog's memory. Similar to humans, dogs generally use two types of memory: short-term and long-term. As any human lucky enough to live with a dog can likely verify, a dog's short-term memory is quite short. In fact, dogs will remember that you fed them or gave them a treat for only about 70 seconds. This likely explains why my dog likes to lick his bowl several times to see if there's any food in it even though he ate less than an hour before.
Dogs' long-term memory is very different from ours. We store information about events or episodes we've experienced (episodic memory) and by recall of general facts (semantic memory). A dog remembers by associating a specific activity with what they see, smell or hear or whether they have a positive or negative memory of it (associative memory). For example, we rescued our current dog who was neglected and very likely abused for the first few years of his life. His first human was a male. When he came to live with us, he seemed very timid and nervous around any males, especially those with deep voices. I can only assume that his interactions with males, especially with a deep voice, were mostly negative and so he associated this negative memory with all males. Fortunately, these negative memories have now been replaced with positive ones and he has no hesitation with men.
Specific sounds associated with food or chews often highlights how associative memory in dogs operates. For example, if my dog hears a certain drawer open (and he can hear it from a floor away), he whips downstairs because he assumes he will get a chew. Associative memory in dogs also highlights why it's critical to correct bad behavior at the time the behavior is being displayed. If you choose to delay disciplining your dog until you get home, for example, for jumping up on someone while you were out on a walk, the incident happened too long ago and your dog will not associate your discipline with the jumping up behavior. This is also the reason that if you punish your dog for peeing on the floor while you were gone (which, by the way you should never do), he/she will have no idea why you are upset.
Many humans wonder whether their dog would remember them if they had to be re-homed or were lost or stolen. We have all read about a dog and his human being reunited after years of separation where the dog clearly remembers his human. But, is this just a one off situation or would most dogs remember their humans? We can look to associative memory for the answer. While your dog may not remember the last day she saw you, she will remember your face, smell, and the many positive feelings associated with you (or negative in the case of a neglectful or abusive human). These associations will continue for the rest of the dog's life.
While dogs form memories around a variety of associations, it's believed that extremely positive or negative experiences are those that are firmly stored in long-term memory. Although though dogs learn throughout their lifetime, they form the most important impressions as puppies. These often emotion laden memories have the power to affect your dog's behavior for a lifetime. This explains why my current dog seems to be "retraumatized" when ever we go on vacation. Even though we leave him in the care of loving, responsible people his reaction to being left is much different than any dog I've had in the past.
By the time he was 2.5 years old, he had been given up twice. As mentioned previously, his first, long-term, human neglected him and more than likely abused him. The second human in his life gave him back to the shelter within 30 days stating that "he ruined everything in their house." Funny enough, he has never destroyed a single thing in our house. It's my belief that the trauma he experienced in his early life has impacted him for a lifetime. When we leave him with others, it seems he associates it with the trauma and abandonment he experienced early on. Now almost 7, this behavior has not changed although we have always come back for him and he has now lived with us for the vast majority of his life. Sadly, I also realize that it is unlikely to ever change.
In reality, a lot about a dog's long-term memory isn't well understood. As more research is being conducted, it's now believed that dogs' long-term memory may be even is more complex than previously thought. As more research is completed, it will be really interesting to learn more. Nonetheless, what is known about the short-term and long-term memory of dogs is both fascinating and instructive. Humans should incorporate this knowledge when they train, discipline and interact with their dogs to not only shape their behavior but to also build stronger bonds with them.