Rapid phonetic learning of Mandarin tones in adults: Daily behavioral improvement and brain activity changes

Behavioral and neural changes related to phonetic learning of foreign speech features can emerge rapidly even in adults. However, most phonetic learning studies have relied on pre- and post-training measurements, offering limited insight into learning dynamics. We investigated short-term Mandarin lexical tone learning in adult Finnish speakers naïve to tonal languages using a four-day training program (1 h/day). Pre- and post-training behavioral measures and change detection event-related potentials during passive and active listening were complemented by day-by-day behavioral assessments. Social learning effects were examined by assigning participants to paired (n = 22) or individual (n = 20) training. Training data revealed distinct temporal dynamics: in both groups, sensitivity to tone changes improved early, whereas tone identification accuracy increased gradually. Paired learners showed enhanced sensitivity to tone changes on the first day compared with individual learners, suggesting co-presence-driven attentional facilitation. Both groups improved in discrimination and categorization speed and discrimination accuracy in the pre- and post-tests. Because these tests used acoustically different tone stimuli from a different speaker than in the training, the results indicate transfer of learning across speakers and phonetic contexts. Neural effects emerged in passive listening. In the mismatch negativity time window, responses to both frequent and rare tones shifted in the negative direction after training, reflecting perceptual attunement to trained pitch contours. P3a amplitude increased to rare tones, indicating enhanced automatic orienting to tone changes. These findings demonstrate rapid behavioral gains and experience-dependent neural changes in adult phonetic learning, including early social facilitation and transfer to acoustically different speech materials.