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New research from teh University of California, San francisco is offering a closer look at how the human brain decodes language, pinpointing a key region responsible for distinguishing individual words within a stream of speech. Published in the journals Neuron and Nature, the studies challenge long-held beliefs about language processing and demonstrate the superior temporal gyrus’s (STG) critical role in identifying word boundaries – a skill honed thru experience. The findings, based on brain activity recordings from 34 volunteers, could have implications for understanding language learning and speech disorders.
Our brains are remarkably adept at processing our native languages, but when faced with unfamiliar sounds, speech can seem like an incomprehensible blur. Now, researchers at the University of California, San Francisco, are shedding light on this phenomenon, revealing how the brain learns to recognize the building blocks of language – and where one word ends and the next begins.
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For years, scientists believed that brain regions responsible for understanding speech were also responsible for identifying word boundaries. However, new research indicates a specific area of the brain, called the superior temporal gyrus (STG), plays a crucial role in this process. Understanding how the brain distinguishes words is fundamental to understanding speech perception and language learning.
Previously, the STG was thought to be involved only in basic sound processing, such as identifying consonants and vowels. But the new studies reveal that this region also contains neurons that learn to track where words begin and end through years of experience listening to a language.
“This demonstrates that the STG doesn’t just hear sounds, but uses experience to identify words as they are being spoken,” said Edward Chang, chief of neurosurgery at the university. “This work provides us with a neural model of how the brain transforms continuous sound into meaningful units.”
Chang led both studies, which were published in the journals Neuron and Nature.
In the Nature study, researchers recorded brain activity from 34 volunteers who were being monitored for epilepsy. The majority of participants were native speakers of Spanish, Mandarin, or English. Eight were bilingual, but none spoke all three languages.
Participants listened to phrases in English, Spanish, and Mandarin – languages they were both familiar with and unfamiliar with.
Researchers found that when participants heard their native language or a language they knew, specialized neurons in the STG were activated. However, when participants heard an unfamiliar language, these neurons remained inactive. This finding suggests the brain relies on prior experience to parse language.
“This explains a little bit of the magic that allows us to understand what someone is saying,” said Ilina Bhaya-Grossman, a doctoral candidate in the UCSF-UC Berkeley Bioengineering Joint Program and one of the authors of the Nature study.
The study published in Neuron further detailed how these specialized neurons detect the start and end of words.
Given that fluent speakers utter several words per second, these neurons need to rapidly reconfigure to register the next word. This rapid processing is essential for real-time language comprehension.
“It’s like a kind of reset, where the brain processes a word it recognizes and then reconfigures itself to start processing the next word,” said Matthew Leonard, associate professor of neurosurgery and co-author of the study.
