Discourse Markers in Spontaneous Dialogue: A Corpus based study of Japanese and English

Discourse Markers in Spontaneous Dialogue: A Corpus based study of Japanese and English Masahito KAWAMORU Takeshi KAWABATA t Nippon Telegraph and Telephone, NTT Basic Research Laboratories t kawamori~atom.brl.ntt.co.jp kaw~idea.brl.ntt.co.j p Akira SHIMAZU" Japan Advanced Institute of Science and Technology" shimazu ~j aist. ac.j p Abstract A spontaneously spoken, natural Japanese discourse contains many instances of the so-called redundant in- terjections and of back-channel utterances. These ex- pressions have not hitherto received much attention and few systematic analyses have been made, since they were regarded as useless, spurious expressions. On the basis of the analysis of spoken dialogue cor- pus, we claim that these utterances have the charac- teristics of discourse markers, which delimit and define units of discourse. Our corpus consists of task-oriented dialogues conducted both in Jacanese and in English. The analysis of the Japanese c,:rpus shows that about half of the turns are started with these so-called redun- dant utterances, while the English corpus shows that about 25 % of the turns start with corresponding En- glish expressions. This suggests that at least in the case oi" Japanese, these so-called redundant utterances have much to do with units of discourse, the building blocks of discourse relations, and that they do indeed function as discourse markers. We show that these utterances comprise a well- defined category, characterizable in a regular manner by their prosodic properties. Prosodic patterns of dis- course markers occurring in the recorded corpus have been analyzed. Several pitch patterns have been found that characterize the most frequently used Japanese dis- course markers. Based on these characteristic pitch pat- terns, a system of discourse markers can be designed so that a relatively small number of basic forms are shown to give rise to most of the discourse markers, with into- nation patterns corresponding to the functions of dis- course markers. Introduction Japanese is an agglutinative language with predomi- nantly verb final sentence patterns. It is to be ex- pected, therefore, that Japanese sentence units are rather easy to recognize, and textbooks and written forms of Japanese indeed vindicate such an expecta- tion. A spontaneously spoken Japanese discourse, however, is full of features which are not part of its written coun- terpart: phrases ending with conjunctions, interjections with verbs attached, unfinished utterances and other disfluencies. Aizuchi, or back-channel utterances, and other so- called redundant utterances, such as hai, un, anoo and ee, are especially abundant in Japanese discourse. These are often taken as the manifestation of the irreg- ularity and non-systematic nature of spoken language. Especially when one wants to recognize 'sentences' in discourse, these utterances inevitably stand in one's way, destroying the sentential structures expected by grammar. Because of these utterances, from the stand point of the conventional grammar, clarifying such mat- ters as which utterances constitute one sentence and which utterances belong to two different sentence units becomes extremely difficult. If the task of discerning sentence units~ the building blocks of discourse, is dif- ficult, the difficulty of discerning discourse structure is enormous. If these utterances …

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