What Sort of Trees Do We Speak? A Computational Model of the Syntax-Prosody Interface in Tokyo Japanese

WHAT SORT OF TREES DO WE SPEAK? A COMPUTATIONAL MODEL OF THE SYNTAX-PROSODY INTERFACE IN TOKYO JAPANESE Pete Whitelock Sharp Laboratories of Europe Ltd. Neave House, Winsmore Lane Abingdon, Oxon., OX14 5UD, Britain ABSTRACT What is the relationship between syntax, prosody and phonetics? This paper argues for a declarative constraint-based theory, in which each step in a derivation adds diverse constraints to a pool. Some of these describe well formed objects in the feature structure domain, in terms of both syntactic and prosodic features. Some characterise the relative prominence of constituents as a partial order over some discrete domain (playing the role of metrical grid). Some are simultaneous equations in the reals, whose solutions represent the pitch level of phonetic objects - high and low tones. The elements of such a theory are illustrated with a treatment of prosodic phrasing and tone scaling in Tokyo Japanese, and the theory is compared to Selkirk and Tateishi's analysis based on the Strict Layer Hypothesis. INTRODUCTION In explorations of the relationship between syntax, phonology and phonetics, it is now generally agreed that hierarchical prosodic representations are an important organising concept. As Pierrehumbert and Beckman (P&B, 1988), vividly put it 'We speak trees, not strings'. One influential view of the geometry of ~ree representations is Selkirk's (1981) Strict Layer Hypothesis. For Selkirk and others, prosodic structures and syntactic structures are objects of different kinds. Yet the nature of the mapping between them remains a question to which explicit, accurate and declarative answers have still to be formulated. This paper presents an alternative view in which phonetic constraints are incrementally associated directly with syntactic derivations. More exactly, derivations must simultaneously meet the well- formedness conditions on syntactic and prosodic labelling, thereby guaranteeing the declarative nature of the syntax-prosody interface. In turn, prosodic labels are associated with a set of equational constraints on phonetic objects. The theory is illustrated with a treatment of prosodic phrasing and tone scaling in standard, i.e. Tokyo, Japanese. The possibility of equating syntactic and prosodic structure in this way follows from a view of syntax with two characteristics. First, some commonly assumed syntactic constituents which never correspond to prosodic units are insufficiently motivated, so such constructions are given an alternative syntactic analysis which respects prosodic constituency. Secondly, the derivation of an expression with a given semantic interpretation, and hence its prosodic structure, may be systematically under-determined by that interpretation. Syntactic structure is thus at least partly motivated by prosodic data, in accord with the concrete view of syntax presupposed in constraint-based grammars. Conversely, the results of Kubozono's (1987) careful phonetic experiments point to the existence of prosodic structures that are organised recursively and in other ways incompatible with the Strict Layer Assumption. Distinctions in syntactic constituency which have been argued to be unimportant for prosodic phrasing do appear to have clear phonetic exponents under controlled conditions, weakening the argument for autonomous prosodic structures. The paper is organised as follows. The elements of the syntactic model used in the analysis of Japanese …

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