Time course and functional neuroanatomy of speech segmentation in adults.

The present investigation was devoted to unraveling the time-course and brain regions involved in speech segmentation, which is one of the first processes necessary for learning a new language in adults and infants. A specific brain electrical pattern resembling the N400 language component was identified as an indicator of speech segmentation of candidate words. This N400 trace was clearly elicited after a short exposure to the words of the new language and showed a decrease in amplitude with longer exposure. Two brain regions were observed to be active during this process: the posterior superior temporal gyrus and the superior part of the ventral premotor cortex. We interpret these findings as evidence for the existence of an auditory-motor interface that is responsible for isolating possible candidate words when learning a new language in adults.