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<Paper uid="E89-1015">
  <Title>FOCUS AND ACCENT IN A DUTCH TEXT.TO-SPEECH SYSTEM</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> This paper deals with the prosodic component of a text-to-speech system for Dutch, more in particular with the rules for assigning pitch accents (sentence accents) to words in an input sentence. Whereas other work on accent rules for Dutch speech synthesis (Kager &amp; Quen6, 1987) did not assume a syntactically analysed input, I will here work from the assumption that the text-to-speech system has a large dictionary as well as a syntactic parser at its disposal.</Paragraph>
    <Paragraph position="1"> The paper is organized as follows: in section 2 I shortly introduce the notions focus and (pitch) accent as I will be using them; as my framework, I will choose the Eindhoven model of Dutch intonation Ct Hart &amp; Cohen, 1973; 't Hart &amp; Collier, 1975) in conjunction with Gussenhoven's (1983) accent placement theory. In section 3 I discuss the rules that connect a domain of focus to an accent on a particular word. The assi~mment of focus domMn~ is dealt with in section 4.</Paragraph>
    <Paragraph position="2"> At the end of this section I s-mrn~O my proposals in the form of an accent assignment algorithm~ In section 5 I present some results obtained in a perceptual evaluation of this algorithm. null 2. A two-stage model of accent placement Work on Dutch intonation at the Institute for Perception Research (IPO) in Eindhoven has resulted in an inventory of elementary pitch movements that make up the occurring Dutch intonation contours ('t Hart &amp; Cohen, 1973; 't Hart &amp; Comer, 1975). The phonetic characteristics of these pitch movements are known precisely, and this knowledge can be used in the synthesis of natural-sounding Dutch intonation contours.</Paragraph>
    <Paragraph position="3"> It was found that some of these elementary pitch movements cause the syllable on which they are executed to be perceived as accented. I will use the term pitch accent or simply accent to refer to prominence caused by the presence of such an accent-lending pitch movement. Of course, the intonation model does not predict where in a sentence pitch accents or intonational boundaries will be located, but when these locations are provided as input, the model is capable of generating a natural-sounding contour. In the remainder of this paper I will deal specifically with pitch accent assiLmment.</Paragraph>
    <Paragraph position="4"> It is relatively standard nowadays to view accent phcement as a process involving two stages (of. Ladd, 1980; Gussenhoven, 1983; Fuchs, 1984; Baart, 1987): in the first stage it is decided which constituents of a sentence contain relatively important information (e.g. because they add new information to the background shared by speaker and hearer) and are therefore to be focussed upon; the decision to focus certain parts of a sentence and not focus other parts is based on semantico-pragmatic information and in principle cannot be predicted from the lexico-syntactic structure of a sentence. In the second stage, the exact location of a pitch accent within a focussed constituent is determined; here lexico-syntactic structure does play a crucial role. The following example, cited from Ladd (1980), illustrates these ideas. (In the examples, pitch accent is indicated by means  of capitaliT~tion.) - III(1) even a nineteenth century professor of  CLASSICS wouldn't have allowed himself to be so pedantic In this case, it is probably the speaker's intention to focus on the subject NP; we can say that all the material from a to classics is \[ +focus\], while the rest of the sentence is \[focus\]. Given the speaker's decision to focus on the subject, an accent is placed by rule on the last lexical element within this constituent. In the following sections, I first discuss the rules that place an accent within a focussed constituent in Dutch, and next turn to the problem of assigning focus to the  constituents of a sentence.</Paragraph>
    <Paragraph position="5"> 3. From focus to accent  As will be clear from the paragraphs above, I assume that accent placement is predictable if the focussing structure of a sentence is known (for discussion see Gussenhoven et al., 1987; Baart, 1987). I adopt Gussenhoven's (1983) idea that accent placement is sensitive to the argument structure of a sentence; however, I replace his semantic orientation by a syntactic one and apply the term argument to any constituent which is selected by the subcategorization frame of some lexical head, indudln~ subjects.</Paragraph>
    <Paragraph position="6"> Input to the accent rules is a binary branching syntactic constituent tree, where apart from syntactic category a node is provided with information concerning its argument status (either argument or not an argument of some lexical head), and where nodes dominating a focussed constituent are assigned the feature \[+focus\], while nodes dominating unfocussed material are \[-focus\]. In order to arrive at an accentuation pattern, three rules and a well-formedness condition are to be applied to this input. A first rule (see (2)) applies iteratively to pairs of sister nodes in the input tree, replacing the syntactic labels with the labels s (for 'strong') or w (for 'weak'), familiar from metrical phonology. By convention, whenever a node is labelled s its sister has to be labelled w and vice versa, the labellings \[s s\] and \[w w\] being excluded for pairs of sister nodes.</Paragraph>
    <Paragraph position="7"> (2) Basic Labelling Rule (BLR): A pair of sister nodes \[A B\] is labelled \[s w\] iff A is an argument; otherwise the labelling is \[w s\].</Paragraph>
    <Paragraph position="8"> The function of the w/s-labelling is to indicate which element of a phrase will bear the accent when the phrase is in focus: after the application of focus assicmment and w/slabelling rules, an accent will be assigned to every terminal that is connected to a dominating \[ + focus\] node by a path that consists exclnsively of s-nodes.</Paragraph>
    <Paragraph position="9"> In (3) I illustrate the operation of the BLR. All left-hand sisters in (3) are labelled w, except for the NP een mooi boek, which is an argument. Granted a focus on the predicate, accent will be assigned to the element boek (there is a path from boek to the \[+focus\] node that consists of s-nodes only).</Paragraph>
    <Paragraph position="10">  (3) (ik) heb een mooi BOEK gekocht  The output of the BLR may be modified by two additional rules. First, the Rhythm Rule accounts for cases of rhythmical accent shift,  see (4).</Paragraph>
    <Paragraph position="11"> (4) Rhythm Rule (RR, applies to the output of the BLR):  Co) B and C are string-adjacent (c) A is not a pronoun, article, ~ preposition or conjunction In (5), where we assume focus on both the main verb and the time adverbial, the accent pattern on the adverbial has been modified by the 1111 (the accent which is normally reali7egi on nacht has been shifted to hele).</Paragraph>
    <Paragraph position="12"> - 112(5) (hij heeft) de HELE nacht GELEZEN he has the whole niEht read</Paragraph>
    <Paragraph position="14"> hele nacht Until now, nothing prevents the label s from being assigned to a node which is \[focus\]. The following rule, adopted from Ladd (1980) takes care of this case. The rule makes sure that a \[-focus\] node is labelled w; by convention, its sister node becomes s.</Paragraph>
    <Paragraph position="15">  While arguments are normally labelled s and therefore likely to receive accent, there are some cases where we do not want an argument to be accented. A case in point are \[-focus\] pronouns. In (Ta) we have an example of a lexical object NP (een speld); in (7b) thi~ NP is replaced by a \[-focus\] pronoun (lets). As a result of the DA rule, it is the particle (op) that receives the accent in (Tb), instead of the  In addition to the rules presented thus far, a well-formedness condition is necessary in order to account for the focus-accent relation. It has been noted by Gussenhoven (1983) that an unaccented verb may not be part of a focus domain if it is directly preceded by an accented adjunct. For instance, in (8a) (8a) (in ZEIST) is een FABRIEK verwoest in Zeist is a factory destroyed the verb (verwoest) is unaccented. There is no problem here: the VP as a whole is in focus, due to the accent on the argument een fabdek. Consider, however, (Sb): (Sb) (in ZEIST) is een FABRIEK door BRAND verwoest in Zeist is a factory by fire destroyed This is a somewhat strange sentence. The accent on door BRAND arouses an impression of contrast and the verb vetwoest is out of focus. A more neutral way to pronounce this sentence is given in (8c): (8c) (in ZEIST) is een FABRIEK door BRAND</Paragraph>
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