Investigation of Learning Trajectory of Mandarin for Tibetan Speakers

When acquiring a spoken language, speakers adapt their speech organs to the articulatory manners and places and thus form a specific articulatory space. For second language (L2) learning, the acquisition process is essentially the one for the learners to approach the standard speech of native speakers in articulatory and acoustical domains by overcoming interferences from their first language. Based on this view, this study investigates learning trajectories in L2 acquisition by measuring the changes in the distance between vowel structures observed from L2 learners and the natives. The vowel structures were constructed for six Mandarin vowels from about 7,200 tokens using the Laplacian eigenmaps. Each vowel was described by a vector with the phase and amplitude of its cluster center and its standard deviation in the vowel structure, and the distance was defined by the difference of the vectors between the learners and the natives. 30 Tibetan Mandarin learners with three Mandarin proficiency levels and 10 Mandarin native speakers participated in this study. The results showed that: i) the higher the Mandarin proficiency of Tibetan speakers is, the closer the structure of their Mandarin vowels is to that of the natives, and ii) the learning trajectory of the six Mandarin vowels, except for vowel /o/, shows a monotonic tendency, that is, as the Tibetan speakers' Mandarin proficiency level increases, the distance reduces for each vowel.