Just ask: What did you have for lunch yesterday? Who were you with? Where were you? Can you picture the scene? The ability to remember things that happened in the past, especially small, retrospective events, is a hallmark of what psychologists call episodic memory. And new research suggests it may be an ability shared by humans and a species of bird called an jay.
Episodic memory “is so named because it involves remembering an event or episode,” said James Davis, lead author of the study published May 15 in the journal PLOS One. “You kind of mentally relive that experience, along with other kinds of details that make up that experience: sounds and sights, and even your thoughts and moods at the time.”
Davies, a PhD student in psychology at the University of Cambridge's Institute of Comparative Cognition, added that episodic memory is different to semantic memory, which involves recalling factual information.
“It's often helpful to think of episodic memory as remembering, whereas semantic memory is just knowing,” he says. “There's really no conscious recall involved.”
Episodic memory is essential to how most people experience the world, but it can be difficult for scientists to prove whether non-human animals have this ability — after all, they can't tell us what they're thinking. But for decades, scientists have been designing experiments to probe animals' abilities to remember past events, and they've found evidence of episodic-like memory in creatures as diverse as pigeons, dogs, and squid.
Corvids (the family of birds that includes ravens and jays) are famously intelligent, and previous research has suggested they have an episodic-like memory that may help them find food they've hidden for later consumption. In 1998, Dr Nicola Clayton designed an experiment with jays that showed the birds could remember what food they had hidden in different locations, and how long ago they had done so.
This method of finding evidence of episodic memory, called the “what, when, where” protocol, has become standard among scientists studying animal memory, but Davis, who is Clayton's mentor, wanted to find a different way to test this cognitive ability.
“If you're only using one methodology, there's a good chance there's some error in that method,” Davis said. “If you use several different methodologies that test the same thing in completely different ways, you get much more conclusive evidence.”
Researchers have devised a new approach using jays, and their findings could have implications for the study of human memory.
Incidental memory test
Davis and Clayton's new experimental design was based on the concept of incidental memory.
“The idea with human episodic memory is that we remember details of an event that aren't necessarily relevant to anything at the time. We weren't actively trying to remember it,” Davis says, “but if you ask us about it a few days later, we might remember that detail.”
This is seemingly unimportant information that you don't consciously remember, like remembering what you had for lunch yesterday. This aspect of episodic memory is sometimes called “mental time travel.”
To test whether jays are capable of mental time travel, the researchers worked with birds that were trained to find food hidden under cups. Davis lined up four identical red plastic cups in a row and had the birds watch as he placed food in one of the cups. The jays then had to remember which cup the food was hidden under. It was pretty simple.
In the next step of the experiment, Davis made some slight tweaks to the appearance of the cups, such as adding stickers or colorful strings, but then hid food underneath the same cups again. To the foraging birds, the strings and stickers were seemingly inconsequential side information; at this point, all they had to care about in order to find the food was the location of the cup.
But in the final stages of the experiment, this little detail in the cups' decoration turned out to be unexpectedly important: Davis moved the cups around, so the birds could no longer rely on the once-important information about which cup contained food. (Food had been removed from the cups to rule out the possibility that the birds were finding the food by smell.) But after a 10-minute break, the jays were still able to find the cups with the food in them.
Davis suggested that the jay's thought process may have involved asking itself, “'Where's the food? I remember going to the place with the black square on it. Let's go there.'” The jay seemed to be reaching back in its memory to recall details about the cup's decoration, and was highly successful in using that information to find the hidden food.
“This study provides strong evidence of episodic memory in jays,” said Dr. Jonathan Crystal, an associate professor of psychological and brain sciences at Indiana University Bloomington, who was not involved in the project. “If you can answer that unexpected question after coincidental encoding, that makes a strong argument that you can remember previous episodes, which is the core of documenting episodic memory.”
The jays choose the same cup during the memory phase of the experiment. (James Davies via CNN Newsource)
Crystal said the study, which aimed to identify animals' ability to form episodic memories, was also important because of its potential role in the field of human memory research.
“The big memory disease is Alzheimer's disease, and of course the most debilitating aspect of Alzheimer's disease is the profound loss of episodic memory,” Crystal said.
He noted that all human Alzheimer's drugs are tested on animals before being tested in people, so it's important for scientists to take a closer look at whether these drugs actually affect memory loss in people with Alzheimer's.
“It's not enough to just improve memory, you need to improve episodic memory,” he said, adding that this could be made possible by better understanding how to test such memories in animals.
