Neural correlates of foreign speech imitation: The effects of age and music.

Adult learners of a foreign speech are often marked by having a foreign accent; however, children and adults with singing training tend to have better pronunciations than adults without music training. The assimilation hypothesis proposes that people tend to assimilate foreign speech to native speech during perception and production, which may explain foreign accent. Unfortunately, the neural mechanisms underlying the age and music effects are still unclear. In this study, we compared brain activation patterns in three groups of participants, namely, children, adults with singing training, and adults without music training (control adults) during native (Chinese) and foreign speech (Spanish) imitation with each word repeated three times. We found greater representational similarity between Chinese and Spanish in both groups of adults than in children during both speech perception and production, supporting the assimilation hypothesis. Furthermore, we found group-specific effects for the similarity between different times of imitation, suggesting different mechanisms. Specifically, control adults showed greater similarity between different times of Spanish word imitation than the other two groups in the medial orbital frontal cortex involved in adaptive learning/memory; children showed greater similarity than the other two groups in the bilateral inferior premotor/postcentral gyri involved in sensorimotor learning; adults with singing training showed greater similarity than the other two groups in the left superior temporal gyrus involved in auditory feedback. It suggests that singing training facilitates reliance on auditory discrimination, while children rely on somatosensory and speech motor control to learn foreign speech sounds, implicating different mechanisms of age and singing training effects. Our results provide insights in understanding the neural mechanisms of age and music effects in foreign speech learning.