Effects of Explicit Phonetic Instruction in Shaping Second-Language Perceptual Cue Weighting: Evidence From English /iː/−/ɪ/

Purpose: This study examined how Chinese second-language (L2) learners of English weight vowel duration and spectral cues in the English /iː/−/ɪ/ contrast at both the group and individual levels. It further explored the role of explicit phonetic instruction from correlational and causal perspectives. Finally, it investigated whether the benefits of training were uniform across learners or varied according to individual differences. Method: The current research adopted a pre–post design with 48 Mandarin-speaking L2 English learners randomly assigned to a control group ( n = 23) and an experimental group ( n = 25). In the pretest and posttest, both groups completed a forced-choice identification task using synthesized “bead–bid” continua covarying in spectral and temporal dimensions. Between the pre- and posttest, the experimental group received explicit phonetic instruction designed to raise their metalinguistic awareness of how vowel spectrum and duration functionally differentiate /iː/ and /ɪ/. Results: At pretest, at a group level, participants primarily relied on duration, although individual variability was substantial and aligned with the perceptual learning stages posited by the Second Language Linguistic Perception (L2LP) model. Explicit instruction reduced reliance on duration in the experimental group, while both groups increased reliance of the spectral cue. Instructional benefits varied across individuals: Learners with initially more balanced cue use and those with prior immersion experience were more likely to shift away from duration. Conclusions: These findings support the generalizability of the L2LP model to Mandarin listeners and demonstrate that explicit instruction can effectively promote cue reweighting, particularly when targeting noncontrastive dimensions in the learners' first language. Instructional outcomes were shaped by prior language experience. Supplemental Material: https://doi.org/10.23641/asha.31402767