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

Although adults learn foreign languages more slowly than children, behavioral improvements can still emerge rapidly with training. Previous phonetic learning studies have mostly focused on pre- and post-training comparisons, leaving daily learning trajectories largely unexplored. Here, in Finnish speakers naive to tone languages, we tracked day-to-day changes in Mandarin tone perception during a short training program (1 h/day for 4 days), complemented by pre- and post-training behavioral and event-related potential (ERP) measures. Each learning session comprised exposure to Mandarin tones in continuous and isolated speech with cues, change detection and identification with feedback, and a listen-and-repeat exercise. To assess the role of co-presence, participants learned either in pairs (n = 22) or individually (n = 20). We found that discrimination and categorization speed, as well as discrimination accuracy, improved from pre-to posttest, with performance also increasing across daily training sessions. Paired learners showed higher sensitivity (d') to tone changes on the first day than individual learners, consistent with co-presence-driven attentional facilitation. At the neural level, P3a amplitude to tone changes during passive listening increased after training, reflecting enhanced automatic orienting to novel sounds at whole group level. These findings demonstrate that short-term training induces rapid behavioral gains and selective neural plasticity in adult phonetic learning, with early co-presence effects and transfer to novel speech sounds.