Japanese Macaques Show Curiosity in Kyoto University Touchscreen Game

Curiosity appears to operate in monkeys much as it does in people. Present them with a task that is overly straightforward and their attention fades. Make it excessively unpredictable and they abandon it.

Find the balance between those extremes, however, and they return to it repeatedly, even when there is no reward available.

Researchers at Kyoto University’s Institute for the Evolutionary Origins of Human Behavior (EHUB) explored this question with a touchscreen hide-and-seek game. Their findings proved more persuasive than they had anticipated.

The Goldilocks theory of curiosity

Curiosity is an unusual drive. It does not depend on rewards: there is no food, mating opportunity or other physical benefit at the end. Instead, it comes from the urge to discover what happens next, what lies ahead or how something functions.

Humans and other animals both show curiosity, but the precise conditions that spark it remain less certain.

A prominent explanation is known as the Goldilocks principle. It suggests that curiosity is directed towards things with a moderate degree of complexity or uncertainty.

When something is too simple, there is nothing left to work out. When it is entirely random, there is no recognisable pattern to pursue. The brain seems to favour a middle position: a challenge that appears possible to solve, without being solved already.

This pattern has been relatively well established in humans, but has received far less attention in other animals.

The Kyoto team set out to examine it in Japanese macaques without using the food rewards that are usually needed to hold laboratory animals’ attention.

A video game for monkeys

To do so, they created a touchscreen game based on a straightforward hide-and-seek format.

Each time a monkey pressed a button, a puppet appeared at a location on the display. Every button generated a different degree of unpredictability.

With low noise, the puppet emerged in a reasonably predictable position. Under high noise, it could appear almost anywhere on the screen. Medium noise produced a result between those two conditions.

The macaques could choose between medium and low noise, as well as between medium and high noise, while the researchers recorded which buttons they selected.

The pattern was clear: they chose medium noise on every occasion. The monkeys repeatedly pressed the button that placed the puppet in a location uncertain enough to remain engaging, but not so unpredictable that it became meaningless.

Like people tackling a puzzle, they appeared attracted to a degree of complexity that seemed worthwhile to explore.

Monkeys kept playing without rewards

The most notable finding was not solely the button the monkeys preferred, but the length of time they continued playing.

In conventional cognitive studies, food is used to motivate monkeys. Without a treat at the end, it is generally assumed that they will soon become uninterested and move away.

That expectation was incorrect.

“In typical cognitive tasks, monkeys are usually given food rewards to keep them motivated, so I was not very confident they would engage with the game without rewards,” said Sakumi Iki, the study’s first author.

“Yet surprisingly, some monkeys worked on this game for nearly 100 trials even without any reward.”

They completed nearly 100 rounds purely for the experience of playing. That is far from insignificant: it is curiosity operating exactly as curiosity should.

Curiosity may benefit more than monkeys

The research was prompted by a practical issue as well as a scientific question. Animals in laboratories and zoos frequently inhabit settings that provide little mental stimulation.

The researchers sought to establish whether games that genuinely stimulate an animal’s curiosity, rather than merely occupy its time, could become a meaningful means of improving animal welfare.

“I originally studied play behavior in wild monkeys, so I have long wanted to create situations in the laboratory where monkeys’ play behavior could emerge naturally,” said Iki.

The researchers hope that results such as these might ultimately harness curiosity to improve the lives of not only monkeys, but also other captive animals.

Measuring monkey enjoyment

Next, the team will investigate whether the macaques genuinely enjoy playing: whether their involvement corresponds with signs of positive emotion, rather than simply repeated button presses.

If so, it would reinforce the argument for curiosity-led games as an animal-welfare tool, rather than only an interesting research method.

There is also something subtly satisfying about the study itself.

The image of a monkey spending a hundred rounds playing hide-and-seek on a touchscreen is striking in its own right. Nothing compelled it to play, and no food reward was waiting afterwards.

Rather, the monkey continued because curiosity compelled it to discover where the puppet would appear next.

Anyone who has fallen into a late-night rabbit hole, reading about something they never needed to know, will recognise precisely how the macaques felt.

The complete study was published in the journal iScience.