Scientists have discovered that chimpanzees and orangutans can use memory cues to remember things — very specific things — weeks to years later, much like humans do.
“There is good evidence challenging the idea that nonhuman animals are stuck in time,” according to Gema Martin-Ordas, a comparative psychologist at Aarhus University in Denmark. Her team conducted a first-of-is-kind study to determine if cues could cause apes to remember a past problem-solving event.
Martin-Ordas told io9 there are two types of long-term memory. Semantic memory is about the things we know — the facts we’ve learned as we’ve lived our lives. Episodic or “autobiographic” memories, on the other hand, are associated with a particular place and time and can be triggered by memory cues. That’s the type of memory we experience when, for example, a scent or a sound suddenly brings an experience from long ago flooding back.
Martin-Ordas and her team wondered whether orangutans and chimpanzees could join together a set of multiple cues they’ve seen only a few times — a process called “binding” and common to humans — to form a memory, and then recall that memory based on seeing those cues.
In a fascinating experiment, Martin-Ordas and her researchers worked with eight chimps and four orangutans at the Liepzig Zoo in Germany in 2009. Taking the apes individually, they showed each one a nice hunk of banana that was placed on a platform hooked to the exterior of a caged testing room. The banana piece could only be retrieved by using a long stick thrust through a slot.
While each ape watched, Martin-Ordas then hid two sticks in another room, only one of which was long enough to reach the banana. After observing all of this activity, the chimp or orangutan was then let loose into the room where the sticks were hidden. To get their treat, they needed to find the right sized stick, take it back to the area where the banana was waiting, and use the stick through the slot to snag the banana.
Martin-Ordas and the apes went through this scenario four times. She hid the sticks in different drawers each time, but the apes always got to see where they were put. They knew that only the longer stick would reach the banana.
Then time went by, during which many other behavorial experiments with Martin-Ordas came and went using the same set of rooms. Amazingly, in 2012 — three years later — 11 of the 12 apes remembered this particular experiment. When placed back into the same room with same researcher and the same banana on a platform, within 5 seconds they began searching the room for the longer stick so they could get their treat.
A set of seven control apes who hadn’t been exposed to the scenario didn’t search for any tool to get to the banana, even after five minutes in the room.
“I was really surprised that they could remember this event and they did it so fast,” Martin-Ordas told ScienceMag.org. She said was testing the apes’ reaction to “a constellation of cues: me, the room, and the specific problem.”
The same apes could also remember a similar experiment two weeks after having seen it only one time. Researchers demonstrated how a ball placed on a see-saw sort of gadget would provide the user a frozen yogurt treat.
Martin-Ordas told the Los Angeles Times that two weeks later, “[i]nstead of showing them the whole event, when they came into the room we only showed them the task. And we used the task, and me, and the room, as the cues to see if we could trigger their memory.” Eleven of 12 apes remembered what to do and got their yogurt treat successfully. (The orangutan who forgot how the first experiment worked accomplished this one successfully, by the way).
Thanks to this research, we’ve learned something we never knew before about our primate cousins, the chimpanzee and the orangutan. Jonathon Crystal, a comparative psychologist at Indiana University, Bloomington told ScienceMag.org, “Three years is a remarkably long time to draw on a memory—not just for animals, but for us. It’s breathtaking.”
Think about these great apes and smile the next time you can’t remember where you put your car keys.
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