Apes know a good thriller when they see one

"When you watch a shocking, emotional event in a movie, you remember the event well, and later on, when you watch the same movie, you anticipate the event," says Fumihiro Kano of Kyoto University in Japan. "Thanks to a recent advance of state-of-the-art eye-tracking technologies, we could examine event anticipation by great apes while watching a movie by means of 'anticipatory looks' to the impending events."

Great apes are already known to have excellent long-term memory skills. However, most studies have examined those skills in the context of food-hiding tests, in which apes see food being hidden and then later retrieve the foods. No one had tested to see whether they could also remember events just by watching them in other contexts.

To find out, the researchers made two short films starring themselves and then showed them to six chimpanzees and six bonobos while tracking their eye movements. In one movie, an aggressive person in an ape suit came out from one of two identical doors. In the other film, a human actor grabbed one of two objects and attacked the ape-like character with it.

The eye-tracking data showed that animals anticipated what they were about to see after a single viewing of the movie. On a second viewing of the first movie, the apes directed their attention to the door where they knew the person dressed as an ape would appear. While watching the second film again, the animals looked in anticipation at the object they knew would soon be used as a kind of weapon, even when that object was placed in a different location than they'd seen earlier.

The findings show that great apes encoded information from the film into their long-term memories and later used that information to anticipate events that were about to happen. And all of that memory is reflected right there in the apes' eyes.

Something else surprised and interested the researchers: the apes really seemed to enjoy the movies. "We were giving juice while showing the videos to them," Kano says, "but some of them even forgot to drink [the] juice and stared at the movies!"

The researchers say they now plan to use anticipatory looks to examine other high-level cognitive functions in the apes, such as the ability to understand that others have beliefs, desires, intentions, and perspectives that differ from their own.