It is nearly impossible to become completely fluent in a second language unless you start before the age of 10, a new study reveals.
Although they struggle to speak fluently, children who start learning after the age of ten can still become ‘very skilled’ linguists.
Scientists have found the window for peak language learning expires around the age of 17 or 18.
This time-frame in childhood is dubbed the ‘critical period’ and scientists still don’t understand why adults struggle with new languages.
It is nearly impossible to learn a language fluently unless you start before the age of 10, a new study reveals. Children remain ‘very skilled’ at picking up new languages until they reach the age of 17 or 18. This time-frame is called the ‘critical period’ (stock image)
The ‘critical period’ makes the most of a supple mind that can absorb new information and adapt to differences in grammar.
Study author Doctor Joshua Hartshorne, an assistant professor of psychology at Boston College, said: ‘If you want to have native-like knowledge of English grammar you should start by about 10 years old.’
Dr Hartshorne, who conducted the study at Massachusetts Institute of Technology (MIT), added: ‘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.’
People who start learning a language between 10 and 18 will still learn quickly, but they have a shorter window before their learning ability declines.
This limited period of time means they don’t achieve the proficiency of native speakers, according to the research.
The findings are based on an analysis of a grammar quiz taken by nearly 670,000 people, which is by far the largest data-set that anyone has assembled for a study of language-learning ability.
Study co-author Professor Josh Tenenbaum, of MIT, said: ‘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.
‘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 said that while it’s typical for children to pick up languages quicker than adults – a phenomenon often seen in families that immigrate to a new country – the trend has been difficult to study in a laboratory setting.
Dr Hartshorne said: ‘Whatever it is that results in what we see in day-to-day life with adults having difficulty in fully acquiring the language, it happens over a really long timescale.’
Following people as they learn a language over many years is difficult and time-consuming, so the researchers came up with a different approach.
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Learning to speak a second language at any point could help keep your brain sharp as you age, a 2015 study found.
The University of Edinburgh detected a pattern of slower mental decline among the bilingual in a group of 835 people born in 1936.
They were given an intelligence test in 1947 at the age of 11, then retested in their early 70s between 2008 and 2010.
A total of 262 participants could communicate in at least one language other than English.
Of those, 195 learnt the second language before the age of 18.
Those who spoke two or more languages had significantly better cognitive abilities in their 70s than their peers.
The strongest effect of bilingualism was seen in general intelligence and reading tests.
They decided to take snapshots of hundreds of thousands of people who were in different stages of learning English.
By measuring the grammatical ability of many people of different ages, who started learning English at different points in their life, they could get enough data to come to some meaningful conclusions.
Within hours after being posted on Facebook, the 10-minute quiz ‘Which English?’ had gone viral.
Dr Hartshorne said: ‘The next few weeks were spent keeping the website running, because the amount of traffic we were getting was just overwhelming.
‘That’s how I knew the experiment was sufficiently fun.’
After taking the quiz, users were asked to reveal their current age and the age at which they began learning English, as well as other information about their language background.
The researchers ended up with complete data for 669,498 people.
Dr Hartshorne said: ‘We had to tease apart how many years has someone been studying this language, when they started speaking it, and what kind of exposure have they been getting: Were they learning in a class or were they immigrants to an English-speaking country?’
The ‘critical period’ makes the most of a supple mind that can absorb new information and adapt to differences in grammar, which drops off at the age of 17 or 18. Scientists do not know how long this period is or why adulthood makes learning a new language harder (stock image)