Effects of individual aptitude on ultrasound biofeedback in non-native vowel production

The purpose of this study is to investigate how individual’s linguistic and spatial knowledge affects the training effects of ultrasound biofeedback. We also examined the influence of vowel differences on the training effect as well as the interaction between individual’s aptitude and training targets. Twenty-eight Taiwan Mandarin native speakers participated in the non-native vowel production experiment. Participants were first assessed by their phonetic awareness, phonological awareness, somatosensory acuity, production variability, and spatial reasoning. Participants were trained to produce non-native Cantonese /ɐ/ and Japanese /ɯ/, provided with ultrasound biofeedback. Cantonese /ɐ/ and Japanese /ɯ/ differ with their closest Mandarin counterparts in vowel height and frontness, respectively. The training effect for each vowel was determined by comparing the tongue postures (in ultrasound) between pre-training baseline and post-training performances. The results and findings are threefold: First, ultrasound biofeedback training in learning non-native sounds can be effective after 20 min of training. Second, more robust training effects were reported for the dimension of vowel height than vowel frontness. Last, individual aptitude indeed predicts the effectiveness of the ultrasound biofeedback training. The interaction between individual’s abilities and training targets can be modulated by common predictors, as well as by predictors that correspond to specific dimensions or are specific to those dimensions. This study highlights the relationship between ultrasound training effects and individual aptitude and at the same time provides insight with regards to the selection of training targets, the methods for magnifying training effect, and the screening test of training effect. These findings crucially lend support to both the theoretical framework of speech production and clinical as well as pedagogical application of ultrasound biofeedback.