Horror Films for Apes Are Teaching Scientists About Long-Term Memory

Eye tracking during scary shows helped scientists reveal that great apes can access memories of single significant events

Great apes, like us, react to a good scare. moodboard/Corbis

Half the fun of watching a scary movie is seeing it for the first time—once you know which room the serial killer uses as a hiding place, there’s no way to replicate the thrill of that initial scream.

Now, one group of researchers has discovered that the same rings true for great apes. These would-be Wes Cravens of the ape world think their findings, published today in the journal Current Biology, have big implications for how scientists think about primates’ memories.

Fumihiro Kano didn’t set out to direct thrillers for apes. The Japan-based researcher is an expert in a cutting-edge technique that lets scientists track apes’ gazes to figure out what grabs and holds their attention. But then Kano teamed up with Satoshi Hirata of the Wildlife Center of Kyoto University to study great apes’ capacity for memory, and he thought of his experience watching apes watch movies.

Great apes found human films “so boring,” he recalls, but they perked up when they watched aggression in films. He wondered if that reaction could help him learn more about great apes’ ability to use their long-term memory.

Since apes can’t use language to access or decode events in their past, scientists have been unable to figure out how to cue memories without turning to techniques like conditioning. This clouds studies of how apes access memories of single events, since conditioning relies on repeating behaviors.

Kano and Hirata wondered if instead they could pair film and eye tracking to learn more about apes’ ability to recall past events. Convinced that violent movies might have what it takes to keep great apes’ attention, they decided to produce a few films of their own.

Using their collective experience with ape behavior, the duo designed two horrific scenarios—one in which beloved caretakers are attacked by a King Kong-like primate, and another in which humans take revenge on an aggressive ape. Armed with a rudimentary script, a camera and an ape costume, they produced two films and showed them to groups of chimpanzees and bonobos while tracking their eye movements. 


“We guessed that 24 hours was long enough to demonstrate long-term memory, but short enough that they’d remember the details,” says Kano. They guessed right. A day later, they showed the apes the videos again. This time, the animals’ eye movements revealed that they were able to anticipate the location of the surprise attacker and the tool used to exact revenge on the fictional ape.

Both bonobos and chimpanzees found the movies terrifying: Not only did their eyes show anticipation of the next scary move, but they also grimaced, vocalized and appeared agitated during the showing. One bonobo was so petrified by the on-screen action that it stopped drinking its grape juice and stared, petrified, as the action played out. 


Kano points out that until now, nobody had known for sure whether apes are capable of accessing long-term memories that aren’t about food. He thinks his team’s research points to intriguing questions about other cognitive skills.

“Now that we know how to determine if an animal recalls a single, really significant event, we can try to duplicate this study with other animals,” he says. He wouldn’t be surprised if human infants, other primates and even other mammals could also access single long-term memories to anticipate events.

But memories are just the beginning, says Kano. Next, he wants to explore whether apes can understand the beliefs or intentions of others—all with the help of his eye tracker and his now-confirmed skills in making movies that can engage (and scare) great apes.

“To humans, this is funny,” he admits, noting that the general public usually “laughs like hell” while watching one of his scary films. “But to apes, this is horrifying.” And who’s to say that romance or even comedy isn’t next for the budding director? Kano chuckles at the idea—and confesses that he doesn’t know of too many other ape auteurs.

“These movies are the peak of years of experience,” he says. “We should be awarded the Ape Oscar or something.” 

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