a smiling man How does the brain process language? It is a question for which scientists did not have a definitive answer until recently. Researchers at the University of California San Francisco (UCSF) conducted a study to determine just how the brain breaks down speech sounds. While scientists have known where the brain handles language for some time, the findings, which indicate that language is processed on the level of linguistic ‘features’, offer deeper insight into the basis of human language.

While some previous studies have analyzed speech processing with only a few sounds or synthesized speech, the scientists at UCSF used spoken natural sentences with a complete range of English phonemes (phonemes are individual sounds like k, n, or o). The participants were six people undergoing surgery related to epilepsy. The researchers monitored their brains by placing neural recording devices directly on the surface of the brain to capture activity in the superior temporal gyrus (STG, also known as Wernicke’s area), which is related to speech perception. The participants listened to 500 unique English sentences uttered by 400 discrete individuals.

The researchers assumed that the STG would be most responsive to phonemes, but they found that the brain actually processes language at a more elemental level using what linguists call features. Features are a reference to the broad aspects of sounds that make up a phoneme. For example, when producing sounds like p, t, or k, there is a small burst of air from the lips. The STG identifies these types of distinctive acoustic patterns to process sounds before it addresses phonemes and larger units of speech.

The findings are a significant step in understanding speech processing. Before this study, scientists knew where in the brain speech was processed, but not how. This information could support further research in language disorders like dyslexia.

“It’s the conjunctions of responses in combination that give you the higher idea of a phoneme as a complete object. By studying all of the speech sounds in English, [what] we found is that the brain has a systematic organization for basic sound feature units, kind of like elements in the periodic table,” said Edward Chang, MD, senior author of the study and associate professor of neurological surgery and physiology at UCSF.

This research is published in the journal Science Express, an online version of Science.

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