Audiovisual high variability phonetic training promotes second language lexical tone learning: An event-related potential study

Abstract

This study investigated the efficacy of a modified high variability phonetic training (HVPT) protocol in second language learning. The target Mandarin lexical tones in the training stimuli were acoustically exaggerated at four levels in terms of duration, pitch range, and pitch contour. Seven audiovisual perceptual training sessions were designed to deliver the training stimuli adaptively based on the listener's identification score. Pre- and post-tests used behavioral identification and discrimination tasks with natural speech, synthetic speech, and non-speech control stimuli. ERP experiments were also conducted with synthetic speech stimuli in a passive listening oddball paradigm. A total of 24 adult monolingual American English speakers were randomly assigned to the training group and control group. Behavioral data showed significant improvement in identifying the four lexical tones in the trainees but not in the controls. There was also training-induced enhancement of categorical perception of the lexical tones for the synthetic speech stimuli. Posttest versus pretest comparison in the trainees showed an increased mismatch negativity (MMN) response with decreased MMN peak latency for the across-category lexical tone stimuli. Collectively, the results demonstrate fundamental neural sensitivity changes at the pre-attentive level underlying training-induced behavioral identification and discrimination changes in second language learners.