Learning a new language is often said to be easiest for young children, but the window is open for much longer than once thought.

According to a new study by a team of researchers from MIT, Boston College and Harvard University, the window is open until the age of 17 or 18.

For the study, the researchers created an online English grammar quiz, so they could use the collected data to analyze the “critical period” for language learning.

“It’s been very difficult until now to get all the data you would need to answer this question of how long the critical period lasts,” Josh Tenenbaum, an MIT professor of brain and cognitive sciences and an author of the paper, said in a statement. “This is one of those rare opportunities in science where we could work on a question that is very old, that many smart people have thought about and written about, and take a new perspective and see something that maybe other people haven’t.”

The researchers also found that it is nearly impossible for people to reach a level similar to that of a native speaker, unless they begin learning a new language by age 10.

“If you want to have native-like knowledge of English grammar you should start by about 10 years old,” Joshua Hartshorne, an assistant professor of psychology at Boston College, who conducted the study as a postdoc at MIT, said in a statement. “We don’t see very much difference between people who start at birth and people who start at 10, but we start seeing a decline after that.”

The paper is published in the journal Cognition.

Team’s new approach

To understand the cognitive process of language learning, the researchers wanted to gather accurate, representative data.

In past research, it was found that children, particularly in immigrant families who move to a new country, tend to pick up languages more easily than adults.

The problem is, this trend is difficult to study in a laboratory setting.

In fact, adults were found to be better at learning under laboratory conditions where both adults and children were taught new elements of a language — a result that did not accurately represent the process of long-term language learning.

So, the researchers came up with a different approach to combat this issue.

Since they wanted to understand language learning from multiple perspectives and stages, they decided to measure the grammatical ability of people at different ages who began learning English at varying points in their lives.

The quiz

To reach a wide-ranging population, Hartshorne decided to create an entertaining grammar quiz, called Which English?, which they hope would go viral.

With the help of MIT undergraduates, he pored over scientific papers on language learning so as to understand English grammar rules that would likely confuse a non-native speaker.

Questions such as “Yesterday John wanted to won the race” were designed to test grammar, while additional questions were included to reveal which dialect the test-taker speaks.

For example, a Canadian English speaker might find the sentence “I’m done dinner” correct, while most others would not.

Hartshorne included these questions to add an enticing, fun aspect to the game.

His strategy worked. Within hours of being posted to Facebook, the quiz went viral.

In total, the researchers collected data on 669,498 people.

After taking the 10-minute-long quiz, users were asked to state their current age, the age in which they began learning English, and additional information about their language background.

“We asked them how much time they had spent in an English-speaking country,” said Hartshorne. “If you have never been to an English-speaking country and you aren’t a native bilingual with an English-speaking parent, you probably aren’t learning in an immersion environment. That’s not certain — they might go to an American school in their country — but it is going to be true enough of the time.”

To analyze the data, the researchers developed a variety of computational models to see which would be most in line with their results.

The findings

They concluded that the best explanation for their results is that grammar-learning ability remains strong until about 17 or 18 years old, when it begins to decline.

This suggests that the critical period for learning a language is much longer than previously thought.

“You have a bit more time than we believed,” said Hartshorne. “But it is also more work and takes longer than we had thought.”

Additionally, the researchers found that while adults are still good at learning foreign languages, they lose an important grammatical ability if they begin learning as a teenager or adult.

Based on their findings, people who start learning a language between 10 and 18 have a shorter window before their ability declines, making it difficult to achieve the proficiency of native speakers.

Implications

Though the research provided surprising information about the critical period of language learning, it is still unknown what causes it to end around age 18.

Hartshorne plans on running some additional studies on non-native language acquisition, as well as studies on grammar and accent learning, to further develop this research.

“We are currently working on doing similar studies in Spanish and Mandarin — two other languages with a lot of non-native speakers,” said Hartshorne.

He also encourages other scientists to make use of their data, which has been made available online, for additional research.

“There are lots of other things going on in this data that somebody could analyze,” he said in a statement. “We do want to draw other scientists’ attention to the fact that the data is out there and they can use it.”