An Effective Hierarchical Graph Attention Network Modeling Approach for Pronunciation Assessment

Automatic pronunciation assessment (APA) manages to quantify second language (L2) learners' pronunciation proficiency in a target language by providing fine-grained feedback with multiple aspect scores (e.g., accuracy, fluency, and completeness) at various linguistic levels (i.e., phone, word, and utterance). Most of the existing efforts commonly follow a parallel modeling framework, which takes a sequence of phone-level pronunciation feature embeddings of a learner's utterance as input and then predicts multiple aspect scores across various linguistic levels. However, these approaches neither take the hierarchy of linguistic units into account nor consider the relatedness among the pronunciation aspects in an explicit manner. In light of this, we put forward an effective modeling approach for APA, termed HierGAT, which is grounded on a hierarchical graph attention network. Our approach facilitates hierarchical modeling of the input utterance as a heterogeneous graph that contains linguistic nodes at various levels of granularity. On top of the tactfully designed hierarchical graph message passing mechanism, intricate interdependencies within and across different linguistic levels are encapsulated and the language hierarchy of an utterance is factored in as well. Furthermore, we also design a novel aspect attention module to encode relatedness among aspects. To our knowledge, we are the first to introduce multiple types of linguistic nodes into graph-based neural networks for APA and perform a comprehensive qualitative analysis to investigate their merits. A series of experiments conducted on the speechocean762 benchmark dataset suggests the feasibility and effectiveness of our approach in relation to several competitive baselines.