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Real quick – what did you have for lunch yesterday? Have you been with anyone? Where were you? Can you picture the scene? The ability to remember things that happened to you in the past, particularly to go back and recall incidental details, is a hallmark of what psychologists call episodic memory – and new research shows it’s a human ability to share with birds called Eurasian jays.
With episodic memory, “you’re remembering an incident or incident, hence the name,” said James Davies, first author of the study published May 15 in the journal PLOS One. “You kind of mentally relive it. It’s also about other types of data that make up that experience, so sounds, sights, even your thoughts or mood at the time.”
Episodic memory differs from semantic memory, which is the ability to recall factual information, said Davies, a doctoral student in psychology at the University of Cambridge’s Comparative Cognition Laboratory.
“It’s often helpful to think of episodic memory as remembering, but semantic memory is just knowing,” he said. “It’s not really a conscious memory.”
Although episodic memory is central to most people’s experience of the world, it can be difficult for scientists to prove whether non-human animals have this ability — after all, they can’t tell us what they intend. However, for decades, scientists have been devising experiments to explore the ability of animals to remember past events, and have found evidence of episodic memory in creatures as diverse as pigeons, dogs and chipmunks.
Cormorants — the group of birds that includes crows, ravens and jays — are well-known, and previous studies have shown they are capable of episodic memory that can help them find bits of food they’ve hidden recently. . In 1998, Dr. Nicola Clayton experimented with scrub scrubbers in which the birds seemed to remember what types of food they had hidden in different spots and how long ago.
This involves finding evidence of episodic recall – known as a “what, when, where” protocol – which is now standard among scientists studying animal memory. But Davies, Clayton’s adviser, wanted to find other ways to test this cognitive ability.
“If you’re only using one methodology, there may be some error in that methodology,” Davies said. “If you use multiple different methodologies that test the same thing in very different ways, that leads to much more conclusive evidence.”
The researchers devised a new approach related to Eurasian jays, and what they found may have implications for the study of human memory.
Testing incidental memory
Davies and Clayton’s new experimental design made use of the concept of contingent memory.
“The idea is that with human episodic memory, we remember details of events that, at the time, were not related to anything. We weren’t actively trying to remember this,” said Davies. “But then if you were asked about it a few days later, you might remember those details.”
It seems like an unimportant piece of information that you haven’t consciously committed to memory – for example, remembering what you had for lunch yesterday. This aspect of episodic memory is sometimes called “mental time travel”.
To find out if Eurasian jays are capable of mental time travel, the researchers worked with birds that were trained to find food hidden under cups. Davies set out a set of four identical red plastic cups and allowed the birds to watch him place a piece of food under one of the cups. Then the reeds had to recall which cup the food was hidden under. Easy enough.
For the next phase of the experiment, Davies made small changes to the appearance of the cups, such as adding colorful stickers or strings, but again hid the food under the same cup in the lineup. For a treat-seeking bird, those strings and stickers seemed less important than incidental information—at this point, they only needed to worry about the location of the cup to find the food.
But in the final stage of the experiment, those little details of cup decoration became unexpectedly important. Davies changed the location of the cups so that the birds could no longer rely on the once crucial information about which cup in the row contained food. (The thorns have since been removed from the cups, to rule out that the birds could find the food by smell.) After a 10-minute break, however, the jars were still able to find the cups with the treats.
Davies suggested that the birds’ mental process may have involved asking themselves, “’Where’s the food? I remember going to the one with the black square on it. I’ll go to that one,’” Davies said. The jays seemed to go back into their memories to find details about the cup decorations, and they were very successful in using that information to find the hidden food.
“This study provides strong evidence for episodic memory in Eurasian diseases,” said Dr. Jonathon Crystal, provost 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 contingent encoding, that’s a strong argument that you can remember back in time to the earlier episode, which is at the heart of documenting episodic memory.”
Crystal said studies like this one, which aim to identify animals’ ability to form episodic memories, are important in part because of their potential role in the field of human memory research.
“Alzheimer’s disease is the major memory disease, and of course, the most debilitating aspect of Alzheimer’s disease is a profound loss of episodic memory,” said Crystal.
Since Alzheimer’s drugs for humans are always tested on animals before reaching human trials, he noted that it is important for scientists to be able to determine whether these drugs affect the type of memories that are lost Alzheimer’s patients.
“It’s not enough to improve memory, we need to improve episodic memory,” he said, and a better understanding of how to test for episodic memory in animals could help do that.
Kate Golembiewski He is a Chicago-based freelance science writer covering zoology, thermodynamics and death.
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