Researchers at the University of California, San Francisco’s (UCSF) Department of Neurological Surgery recently published a study which sheds light on the nature of speech perception in non-native languages. The study, which was conducted on patients with epilepsy, is one of the first to provide linguists and cognitive scientists with insight into how brain activity changes as individuals advance in a second language.
“With this study, we were able to see what’s actually happening in the brain regions involved in differentiating sounds during this initial phase of learning,” said Matt Leonard, one of the study’s principal investigators and an assistant professor of neurological surgery at UCSF.
For this study, the researchers looked into how individuals’ ability to perceive subtle differences in non-native phonemes changes with exposure and practice with the phonemes. Subjects participating in the study were native English speakers who were exposed to the tonal contrasts of Mandarin Chinese.
Mandarin is well-known across the world for its four-way tonal contrast — depending upon the pitch a speaker produces when pronouncing a syllable in Mandarin, the meaning can, and typically does, change (i.e., the syllable “ma” means “mother” when produced with a high, flat tone, while it means “scold” when produced with a high, falling tone). English, on the other hand, does not have such a tonal contrast — words are not differentiated according to the pitch of individual syllables in the same way that Mandarin is.
The participants of the study consisted of a group of epilepsy patients at UCSF and the University of Iowa, who had each had previous brain surgeries in which electrodes were implanted in their brain — these electrodes were originally used to identify the location of their seizures. The electrodes allowed the researchers to identify the regions of the brain that were most active during the process of identifying the differences between certain Mandarin syllables, which consisted of the same consonant-vowel pattern and a different tone.
Over time, the researchers found that each individual processed different tones slightly differently, which could possible account for individual differences in the language learning process. Different tones tended to activate different regions of the brain, however, which region was most heavily activated for each tone appeared to vary for each patient. “It’s more like each person’s brain has a unique set of knobs that are getting fine-tuned while they’re becoming familiar with these sounds,” Leonard said.
“The volunteers were able to learn the tones in Mandarin without affecting their ability to perceive pitch in English or in music,” he added. “These little neural knobs were all communicating with each other to reach the point where they can do the task correctly by working together.”