Why is it so difficult for adults to learn a second language?

This somewhat surprising result allowed the research team to understand how the brain weighs between neuroplasticity and stability

Dr.

By using electrodes on the surface of the brain to track high-resolution neural signals, the research team found that as listeners become familiar with unfamiliar sounds, clusters of neurons scattered in the language cortex seem to fine-tune themselves

"This is the first time we have a deep understanding of what happens in the brain between hearing foreign language sounds for the first time and being able to recognize them," said Leonard, the lead researcher of the study

He said: "This intermediate stage is a crucial step in language learning, but it is difficult to handle because this process is dynamic and unique to everyone

When strange sounds become familiar, brain activity also changes

Leonard said that learning the pronunciation of a new language is the first step in learning to use the language

The team worked with 10 patient volunteers, whose mother tongue is English, aged between 19 and 59, and asked them to recognize the pronunciation of Mandarin Chinese

Each of the volunteers had previously undergone brain surgery, during which electrodes were implanted in their brains to determine the source of the seizures

In the next few days, Leonard and Yi worked with volunteers to play several recordings of men and women of different ages and native Mandarin speakers, using each of the four tones to utter the "horse".

Leonard said that after this short period of time, people have passed the initial stages of learning, and to some extent proficiently classify sounds

He added: "We have also found a lot of changes

Learning new sounds requires fine-tuning the nerve "knob"

When observing the neural signals produced by language learners, they saw a pattern that both surprised them and explained the performance curve they observed

Other published research data indicate that when a person becomes more familiar with language, the activity of the entire language cortex may increase

Yi said that these changes may be related to the regulation of certain tones in a certain area of ​​the brain

"We can see that when people hear the down tone, some groups of cells will respond more strongly to the down tone, while the other group of cells next to it will respond more and more strongly to the down tone," Yi said

In addition, different people, different tones will make which brain area is more active

"It's more like everyone's brain has a unique set of knobs, and when they become familiar with these sounds, these knobs will be fine-tuned," Leonard said
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This may explain why some people learn pronunciation more easily than others, because each individual’s unique brain seeks its own balance between maintaining the stability of the native language and the plasticity required to learn a new language
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Leonard said: "Volunteers can learn the tones of Mandarin without affecting their perception of English or music tones
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These small neural knobs communicate with each other and reach a point where they can complete the task correctly through cooperation
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Han G.
Yi, Bharath Chandrasekaran, Kirill V.
Nourski, Ariane E.
Rhone, William L.
Schuerman, Matthew A.
Howard III, Edward F.
Chang, and Matthew K.
Leonard.
Learning nonnative speech sounds changes local encoding in the adult human cortex .
PNAS , 2021 DOI: 10.
1073/pnas.
2101777118