Prosody, Syntax and Parsing

PROSODY, SYNTAX AND PARSING John Bear and Patti Price SRI International 333 Ravenswood Avenue Menlo Park, California 94025 Abstract We describe the modification of a grammar to take advantage of prosodic information provided by a speech recognition system. This initial study is lim- ited to the use of relative duration of phonetic seg- ments in the assignment of syntactic structure, specif- ically in ruling out alternative parses in otherwise ambiguous sentences. Taking advantage of prosodic information in parsing can make a spoken language system more accurate and more efficient, if prosodic- syntactic mismatches, or unlikely matches, can be pruned. We know of no other work that has suc- ceeded in automatically extracting speech informa- tion and using it in a parser to rule out extraneous parses. 1 Introduction Prosodic information can mark lexical stress, iden- tify phrasing breaks, and provide information useful for semantic interpretation. Each of these aspects of prosody can benefit a spoken language system (SLS). In this paper we describe the modification of a gram- mar to take advantage of prosodic information pro- vided by a speech component. Though prosody in- cludes a variety of acoustic phenomena used for a variety of linguistic effects, we limit this initial study to the use of relative duration of phonetic segments in the assignment of syntactic structure, specifically in ruling out alternative parses in otherwise ambiguous sentences. It is rare that prosody alone disambiguates oth- erwise identical phrases. However, it is also rare that any one source of information is the sole feature that separates one phrase from all competitors. Tak- ing advantage of prosodic information in parsing can make a spoken language system more accurate and more efficient, if prosodic-syntactic mismatches, or unlikely matches, can be pruned out. Prosodic struc- ture and syntactic structures are not, of course, com- pletely identical. Rhythmic structures and the neces- sity of breathing influence the prosodic structure, but not the syntactic structure (Gee and Grosjean 1983, Cooper and Paccia-Cooper 1980 ). Further, there are aspects of syntactic structure that are not typically marked prosodically. Our goal is to show that at least some prosodic information can be automatically ex- tracted and used to improve syntactic analysis. Other studies have pointed to possibilities for deriving syn- tax from prosody (see e.g., Gee and Grosjean 1983, Briscoe and Boguraev 1984, and Komatsu, Oohira, and Ichikawa 1989) but none to our knowledge have communicated speech information directly to a parser in a spoken language system. 2 Corpus For our corpus of sentences we selected a subset of a corpus developed previously (see Price et aL 1989) for investigating the perceptual role of prosodic infor- mation in disambiguating sentences. A set of 35 pho- netically ambiguous sentence pairs of differing syntac- tic structure was recorded by professional FM radio news announcers. By phonetically ambiguous sen- tences, we mean sentences that consist of the same string of phones, i.e., that suprasegmental rather than segmental information is the basis for the distinction between members of the pairs. Members of …

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