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Very quickly: what did you eat yesterday? Were you with someone? Where were you? Can you imagine the scene? The ability to remember things that happened to you in the past, especially to go back and remember small incidental details, is a hallmark of what psychologists call episodic memory – and new research suggests that this is an ability that humans can share with birds called Eurasian jays.
With episodic memory, “you remember an event or an episode, hence the name,” says James Davies, first author of the study published May 15 in the journal PLOS One. “You relive it mentally. It’s also about other details that make up that experience, like sounds, sights, even your thoughts or your mood at that moment.”
Episodic memory differs from semantic memory, which is the recall of factual information, added Davies, a doctoral student in psychology at the University of Cambridge’s Comparative Cognition Lab.
“It is often useful to think of episodic memory as remembering, while semantic memory is just knowing,” he said. “There is not really a conscious recall.”
Although episodic memory is an integral part of how most humans experience the world, it can be difficult for scientists to prove whether non-human animals share this ability; after all, they can’t tell us what they think. However, scientists have been devising experiments for decades to delve into animals’ ability to remember past events, and they’ve found evidence of episodic memory in creatures as varied as pigeons, dogs and squids.
Corvids (the group of birds to which crows, ravens and jays belong) are known for their smartness, and previous studies have suggested that they are capable of episodic memory, which may help them find bits of food they have for later hidden. In 1998, Dr. Nicola Clayton devised an experiment with scrub jays in which the birds seemed to remember what kind of food they had hidden in different places and how long ago.
This way of finding evidence of episodic-like memory – called a “what, when, where” protocol – has become standard among scientists studying animal memory. But Davies, Clayton’s advisor, wanted to find other ways to test this cognitive ability.
“If you only use one methodology, there may be an error in that method,” says Davies. “If you use multiple different methodologies that test the same thing in very different ways, it leads to much more compelling evidence.”
The researchers came up with a new approach involving Eurasian jays, and what they discovered could have implications for the study of human memory.
Incidental memory testing
Davies and Clayton’s new experimental design was based on the concept of incidental memory.
“The idea is that with human episodic memory we remember details of events that were not relevant to anything at the time. We weren’t actively trying to remember this,” Davies said. “But if you were asked about it a few days later, you might remember those details.”
It’s a seemingly insignificant piece of information that you haven’t consciously committed to memory, for example remembering what you ate for lunch yesterday. This aspect of episodic memory is sometimes called “mental time travel.”
To find out whether Eurasian jays are capable of mental time travel, the researchers worked with birds trained to find food hidden under cups. Davies set up a row of four identical red plastic cups and showed the birds how he placed a piece of food under one of the cups. The jays then had to remember under which cup the food had been hidden. Easy enough.
For the next step of the experiment, Davies made minor changes to the appearance of the cups, such as adding stickers or colorful strings, but again hid the food under the same cup in the setup. To a bird looking for a treat, those strings and stickers were seemingly unimportant additional information – at this point all they had to worry about was positioning the cup to find the food.
But in the final phase of the experiment, those small details of the cup decoration became unexpectedly important. Davies changed the position of the heads so that the birds could no longer rely on the once crucial information about which head in the row contained food. (The treats had been removed from the cups by now, to rule out the possibility that the birds found the food by smell alone.) However, after a 10-minute break, the jays were still able to find the cups containing 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’m going there,” Davies said. It seemed that the jays went back into their memories to retrieve 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 jays,” 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 incidental encoding, it becomes a strong argument that you can recall back in time to the earlier episode, which is at the heart of documenting episodic memory.”
Crystal said studies like these, which aim to identify animals’ abilities to form episodic memories, are important in part because of their potential role in the field of human memory research.
“The great disease of memory is Alzheimer’s disease, and the most debilitating aspect of Alzheimer’s disease is of course a profound loss of episodic memory,” Crystal said.
Because Alzheimer’s drugs for humans are invariably tested on animals before they are tested on humans, he noted that it is important that scientists can determine whether these drugs actually affect the types of memories that Alzheimer’s patients lose.
“It’s not enough to just improve memory, we need to improve episodic memory,” he said, and a better understanding of how to test for episodic memory in animals could make that possible.
Kate Golembiewski is a freelance science writer based in Chicago who delves into zoology, thermodynamics and death.
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