MAS.632 Conversational Computer Systems - MIT OpenCourseWare

Higher Levels of Linguistic Knowledge
Chapter 1 presented an analysis of human voice communication as a hierarchical
stack of linguistic layers. In this schema (depicted in Figure 1.1), each layer
of the stack is progressively more removed from the acoustical events associated
with speech. The higher layers pertain to the meaning and intention of an
utterance rather than to the actual sounds used to convey individual words.
As proposed in Chapter 1, analyzing conversation into layers is useful for computational
purposes because each layer is likely to necessitate its own representation.
The discussion of speech recognition and synthesis technologies emphasized
the lower linguistic layers of communication, i.e., speaking or recognizing words.
Syntactic and semantic constraints were introduced as aids to connected speech
recognition and influences on intonation and stress. The previous chapter focused
on interactive techniques to recover from speech recognition errors with the goal
of properly decoding the words in an input utterance. From the user's perspective,
speech recognition is not about identifying words; rather, it is a means
whereby a computer system understands and acts upon the user's desires. Performance
and utility of speech systems are ultimately judged against the highest
layers of speech understanding. To this end, this chapter presents representations
of syntactic, semantic, pragmatic, and discourse structure that serve the
reader as an introduction to topics in natural language processing. The chapter
includes several case studies to illustrate the wide range of conversational interactions
made possible by models of discourse.