Perceptual overshooting in second language prosody: A non-linear restructuring of English boundary cues among Mandarin-English learners

The perception of prosodic phrase boundaries remains a core difficulty for second language (L2) learners. Drawing on the categorical perception framework, which examines how listeners apply continuous or categorical auditory memory strategies (i.e., gradient or categorical perception) to map acoustic waves onto linguistic representations, this study investigates the effects of acoustic properties, first language (L1) transfer, and L2 proficiency on the perception of L2 prosodic boundaries cues. Three experiments were conducted to assess the perception of three specific boundary cues (pauses, final lengthening, and pitch). Participants included English-speaking monolinguals along with Mandarin L1 speakers with high- and low-proficiency in L2 English. The results revealed that the degree of categorization was descending: pauses > final lengthening > pitch, demonstrating that physical properties significantly influence the perception of boundary acoustic cues. Furthermore, for lengthening and pitch cues, the high-proficiency L2 group exhibited sharper identification slopes and higher discrimination peaks than monolinguals. This overshooting effect reflects a non-linear developmental trajectory in L2 prosody acquisition. These findings challenge the traditional view of L2 speech perception, which assumes that learners gradually and linearly acquire native-like speech.