Is talker variability a critical component of effective phonetic training for nonnative speech?

The current investigation adopted high variability phonetic training with additional audiovisual input and adaptive acoustic exaggeration to examine the role of talker variability. Sixty native Chinese-speaking adults were randomly assigned to a multiple-talker (MT) training group, a single-talker (ST) training group, and a control (CTRL) group without training. The target sounds were the English /i/-/ɪ/ contrast, delivered in 7 sessions using minimal pair word lists. Pre- and post-tests employed natural word identification, synthetic phoneme identification, and word production. Unlike the CTRL group, both training groups showed significant identification improvements, and the effects generalized to novel talkers and new phonetic contexts. Although training did not improve speech intelligibility, there was a significant gain in the use of the primary spectral cues and a decrease in the secondary durational cue. No differences were observed between the MT and ST groups. By removing the “enhancement” features, however, the training program with independent samples was able to verify the advantages of MT over ST training. These results provide the first evidence for the efficacy of other facilitative training features, independent of talker variability, in retuning second language learners’ attention to critical acoustic cues for the target speech contrast and producing transfer of learning.