Neural changes accompanying overnight nonnative phonetic learning

Abstract

Sleep is important in the consolidation of learning, including the perceptual learning of non-native speech sounds. Previous work investigating the role of post-training sleep on nonnative phonetic learning has demonstrated that sleep significantly improves identification for a trained talker in the absence of further training. In addition, sleep appears to facilitate generalization of learning to non-native tokens produced by an untrained talker. We investigated the neural correlates of these behavioral observations using fMRI. Participants were trained in the Hindi dental-retroflex contrast in the evening on Day 1. Immediately following training, participants performed the category identification task in the scanner, and then again 12 hours later. Sleep duration was monitored via wrist Actigraphs. On Day 1, significant differences in activation for the Trained vs. Untrained Talker were identified in the supramaginal gyrus and adjacent parietal areas, whereas on Day 2, activation for both talkers was observed to move into the temporal lobes bilaterally. After sleep, and in the absence of further training, decreases in activation were observed in right superior temporal gyrus, right precentral gyrus, and left prefrontal cortex. Based on these findings, we argue that newly acquired nonnative sounds are processed in classic (i.e., more native-like) speech regions following sleep.