Apes remember major events in movies, even on a single viewing

Hooked (Image: Bernd Weissbrod/EPA/Corbis)

We all have our favourite movie moments, ones we love to watch again from time to time. Now it seems chimpanzees and bonobos, too, have the nous to recall thrilling scenes in movies they have previously seen and anticipate when they are about to come up.

The results suggest apes can readily recall and anticipate significant recent events, just by watching those events once.

Rather than use hidden food as a memory test, Japanese researchers made short movies and showed them to apes on two consecutive days.

“We showed a movie instead, and asked whether they remember it when they only watch an event once, and an event totally new to them,” says Fumihiro Kano of Kyoto University in Japan. “Their anticipatory glances told us that they did.”

Plot moment

Kano and his colleague Satoshi Hirata made and starred in two short films. Another of the characters was a human dressed up as an ape in a King Kong costume who carried out attacks on people, providing the key plot moment in the first movie (see video).

Both films were designed to contain memorable dramatic events, and the researchers deployed laser eye-tracking technology to see if the animals preferentially noticed and remembered these moments.

“In our previous studies we found that apes seem to remember emotional events rather than neutral ones, just like humans do,” says Kano. The researchers hoped that enacting an emotionally charged scene involving aggression would help them tease out any inklings of memory.

In the first of the two 30-second-long movies, the ape character bursts in through the door on the right – one of two visible on screen – and attacks one of the two people 18 seconds in.

Through tracking the gaze of six chimpanzees and six bonobos, the researchers found that on a second viewing, the animals preferentially looked at the right-hand doorway around 3 seconds before the ape burst in, demonstrating recall of locational content.

The second movie allowed them to show that the apes could also remember what items were relevant to a plot.

Weapon swap

In the first screening, a human character chose one of two adjacent weapons to launch a revenge attack on the ape 24 seconds in. Cunningly, the second screening used a slightly different version which swapped the positions of the two weapons.

The animals focused their anticipatory glances on the weapon used in the first showing, not where it had been in the first showing, demonstrating that they knew what it would be used for and their expectation that the character would select it again, even though it was in a different place.

“The fact they remembered such details from the previous video was really impressive,” says Kano. He speculates that these skills could potentially be important for survival in the wild, enabling the apes to anticipate and avoid impending danger, to increase social learning by remembering what other apes did, and to negotiate social environments that require memory of cooperative and competitive norms.

Other primate cognition researchers hailed both the result and the idea of using movies to tease it out.

“The authors provide new evidence that apes really are remembering past episodes,” says Laurie Santos of Yale University, who previously investigated how capuchin monkeys react to advertisements specifically made for them.

“Their study goes way beyond the sorts of planning tasks used in previous experiments, showing that apes not only have memories of specific events but also that they’re tracking some of the emotions associated with those events,” she says. “The study may be a real game changer to debates about these episodic memories in animals.”

“This is a nice demonstration of involuntary event memory in chimpanzees and bonobos,” says Josep Call of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “I anticipate this elegant new technique will be adopted by many researchers to investigate what aspects of events apes and other species find memorable.”

The technique’s potential has not been lost on the Japanese duo, who are already planning to reuse it. “We can ask if apes understand other agents’ goals, intentions and beliefs,” says Kano. “Understanding a story plot is cognitively demanding, so a story is useful to examine their cognition.”

Journal reference: Current Biology, DOI: 10.1016/j.cub.2015.08.004