Here’s Why Words Blur Together When You Listen to a Foreign Language

It’s a lesson that many language learners have learned the hard way: While the words of a familiar language are distinct, the words of an unfamiliar one are often tricky to tease apart, blurring together as a single sound. But why does the brain have such an easy time distinguishing between words in one language, and such a tough time distinguishing between them in another? Does it have to do with your brain, or with the language itself?

According to a pair of parallel studies published in Nature and Neuron, the difference is all thanks to experience. Concentrating on an area of the brain’s temporal lobe called the superior temporal gyrus (STG), the two studies suggest that specialized neurons in the STG learn to identify the beginnings and ends of words over time, after years of exposure to a given language.

“This shows that the STG isn’t just hearing sounds, it’s using experience to identify words as they’re being spoken,” said Edward Chang, the corresponding author of the two studies and a neuroscientist at the University of California, San Francisco, according to a statement. “This work gives us a neural blueprint for how the brain transforms continuous sound into meaningful units.”

Read More: How Learning a Language Changes Your Brain

Familiar and Unfamiliar Languages

When we listen to a familiar language, we easily discern the starts and stops of words, even when they’re barely there. It was long theorized that the STG was uninvolved in this discernment. In fact, the area was once believed to be implicated in only the simplest sound processing, including the isolation of consonant and vowel sounds.

Putting that theory to the test, Chang and a team of researchers took brain recordings of a handful of participants as they heard bits of both familiar and unfamiliar languages. The results revealed that the brain actually learns language patterns in an unexpected place over time, with the STG’s neurons gradually gaining experience in discriminating between words.

Read More: When Did Humans Evolve Language?

Neurons Listen and Learn

Gathering a group of 34 participants for the Nature study, the researchers worked with both monolingual and bilingual individuals, 26 of whom spoke English, Spanish, or Mandarin and eight of whom spoke English and Spanish.

Recording their brain activity as they listened to segments of speech in all three languages and analyzing the recordings with machine learning models, the researchers determined that specialized neurons in the STG behaved differently depending on the language that the participants had heard — activating when they listened to a familiar language and remaining inactive when they listened to an unfamiliar one.

“It explains a bit of the magic that allows us to understand what someone is saying,” said Ilina Bhaya-Grossman, a co-author of the two studies and a Ph.D. student at the University of California, San Francisco, according to the statement.

Starting and Stopping With Words

In the Neuron study, meanwhile, the researchers rounded up a total of 16 participants and turned to brain recordings to demonstrate that these specialized neurons in the STG activate and deactivate in time with the beginnings and ends of words, turning on and turning off as a way to separate speech into smaller components.

“It’s like a kind of reboot, where the brain has processed a word it recognizes, and then resets so it can start in on the next word,” said Matthew Leonard, a co-author of the two studies and a neuroscientist at the University of California, San Francisco, according to the statement.

Providing insights into the importance of language exposure and clarity into the distinctive challenges that differentiate the process of learning a language earlier on or later on in life, the research also contextualizes why injuries to the STG can cause such significant damage to a person’s speech processing abilities.

Read More: Hand Gestures May Have Been the Start of Human Language

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