Training-induced brain activation and functional connectivity differentiate multi-talker and single-talker speech training.

In second language acquisition studies, the high talker variability training approach has been frequently used to train participants to learn new speech patterns. However, the neuroplasticity induced by training is poorly understood. In the present study, native English speakers were trained on non-native pitch patterns (linguistic tones from Mandarin Chinese) in multi-talker (N = 16) or single-talker (N = 16) training conditions. We focused on two aspects of multi-talker training, voice processing and lexical phonology accessing, and used functional magnetic resonance imaging (fMRI) to measure the brain activation and functional connectivity (FC) of two regions of interest in a tone identification task conducted before and after training, namely the anterior part of the right superior temporal gyrus (aRSTG) and the posterior left superior temporal gyrus (pLSTG). The results showed distinct patterns of associations between neural signals and learning success for multi-talker training. Specifically, post-training brain activation in the aRSTG and FC strength between the aRSTG and pLSTG were correlated with learning success in the multi-talker training group but not in the single-talker group. These results suggest that talker variability in the training procedure may enhance neural efficiency in these brain areas and strengthen the cooperation between them. Our findings highlight the brain processing of newly learned speech patterns is influenced by the given training approach.