Researchers are looking at how speech sounds are identified by the brain; researchers have long known where speech is processed, but little research has been done on how the process works.
The team found the brain does not respond to phonemes (speech segments like the "b" in boy) but rather detects simpler elements called "features," a University of California-San Francisco news release reported.
The finding could help us better understand reading disorders, which may occur when printed words are imperfectly mapped onto speech sounds," the news release reported.
"This is a very intriguing glimpse into speech processing," Edward F. Chang, MD, senior author of the new study and associate professor of neurological surgery and physiology said in the news release. "The brain regions where speech is processed in the brain had been identified, but no one has really known how that processing happens."
Past studies have only looked at how the brain responds to certain speech sounds, this new research took a complete inventory of the phonemes included in the English language.
The team attached neural recording devices to the brains of six epileptic patients. The patients listened to 500 unique sentences spoken by 400 people while the researchers recorded activity in the superior temporal gyrus.
Most researchers would expect the brain cells to respond to phonemes, but found that instead certain regions of the STG responded to features.
"These regions are spread out over the STG," first author Nima Mesgarani, PhD, now an assistant professor of electrical engineering at Columbia University, who did the research as a postdoctoral fellow in Chang's laboratory. "As a result, when we hear someone talk, different areas in the brain 'light up' as we hear the stream of different speech elements."
"Features" are "distinctive acoustic signatures created when speakers move the lips, tongue or vocal cords," the news release reported. The brain put these things together to understand phonemes.
"It's the conjunctions of responses in combination that give you the higher idea of a phoneme as a complete object," Chang said. "By studying all of the speech sounds in English, we found that the brain has a systematic organization for basic sound feature units, kind of like elements in the periodic table."
