Exploiting Prosody for Automatic Syntactic Phrase Boundary Detection in Speech

The relation between syntax and prosody is evident, even if the prosodic structure cannot be directly mapped to the syntactic one and vice versa. Syntax-to-prosody mapping is widely used in text-to-speech applications, but prosody-to-syntax mapping is mostly missing from automatic speech recognition/understanding systems. This paper presents an experiment towards filling this gap and evaluating whether a HMM-based automatic prosodic segmentation tool can be used to support the reconstruction of the syntactic structure directly from speech. Results show that up to 85% of syntactic clause boundaries and up to about 70% of embedded syntactic phrase boundaries could be identified based on the detection of phonological phrases. Recall rates do not depend further on syntactic layering, in other words, whether the phrase is multiply embedded or not. Clause boundaries can be well assigned to intonational phrase level in read speech and can be well separated from lower level syntactic phrases based on the type of the aligned phonological phrase(s). These findings can be exploited in speech understanding systems, allowing for the recovery of the skeleton of the syntactic structure, based purely on the speech signal