Non-native perception and learning of the phonemic length contrast in spoken Japanese: Training Korean listeners using words with geminate and singleton phonemes

To establish an effective training paradigm for a computer-assisted language learning system that enables non-native learners to exploit native-like perceptual cues for identifying length contrasts, e.g., consonant length, in the Japanese language (hereafter, Japanese length contrast), two experiments were conducted to investigate the identification accuracies of native Korean listeners before and after intensive perceptual training. The first experiment assessed the perceptual characteristics that native Korean listeners show when identifying the length contrast in the face of variation in speaking rate. The results suggested that native Korean listeners identify length contrasts by relying on a fixed-length criterion instead of adapting to changes in speaking rate. Also, Korean listeners showed a noticeable bias toward geminate responses for all speaking rates, with a stronger bias for slower speaking rates. The second experiment was based on these perceptual characteristics of Korean listeners. It investigated the extent to which intensive training helps improve listeners' ability to identify Japanese length contrast and to examine whether greater stimulus variability during training leads to more robust training effects. The overall results showed that the perceptual training improved Korean listeners' ability to perceive consonant length contrast. Moreover, misidentification of geminates decreased at post-test. However, the effect of training did not differ greatly between conditions of high stimulus variability during training (training with three speaking rates) and low stimulus variability (training with a single speaking rate). Training also did not generalize to perception of untrained contrast type (vowel length contrast). These results suggest that while perceptual training helps Korean learners learn a new, difficult-to-learn L2 phonemic length contrast, it is still difficult for learners to acquire native-like perceptual criteria.