Download Bill G`s Template, Rules and Tips

STEMMA: a new system for multilingual semio/syntactic parsing
for applications to synthetic speech prosodic stylization
Per Aage Brandt* and Patrizia Bonaventura**
*Department of Modern Languages and Literatures
**Department of Communication Sciences
The generation of phrasal structure is based on
an order of dominance presided by a finite verb,
under which the complements (considered as
“actants” and “circonstants” are organized. The
semantic nodes corresponding to the
complements under the finite verb (head) are
generated according to the following order:
ABSTRACT
The goal of the present study consists in testing the applicability of the
stemmatic model of semio-syntactic analysis, realized by Prof. Brandt (Brandt,
1973; 2004), as a part of the text processing component of a Text-To-Speech
system, to perform multilingual semio-syntactic parsing, in order to automatically
predict accurate melodic contours for speech synthesis. Existing parsers,
usually based on dependency grammar (CONNEXOR, Järvinen and
Tapanainen, 1997), generative (Chomskyan) grammars (Marcus, Santorini, and
Marcinkiewic, 1993), and ‘form and function’ grammars (Visual Interactive
Syntax Learning), process sentences according to the hierarchy corresponding
to their syntactic structure, therefore, needing to resort to a separate semantic
component to disambiguate polysemic expressions.
1. Subject complement (S1 = s(S, finite verb))
2. Predicative complement (S2 = s(S, S1))
3. Object complement (S3 = s(S, S2))
4. Telos complement (i.e. indirect object, as
dativ; S4 = s(S, S3))
5. Arche’ complement (i.e. “agent”, or origin
of action; S5 = s(S, S4))
6. Topos complement (i.e. “time” and “place”
adverbial expressions; S6 = s(S, S5))
7. Logos complement (i.e. adverbial
categories of “logical” determination,
or “manner”; S7 = s(S, S6))
8. Junctive complement (expresses
“coordination” or “juxtaposition”; S8=
s(S, S7)))
STEMMA, on the contrary, provides a semio-syntactic integrated processing of
words and POS. Also, STEMMA differs form other Head-Driven Phrase
Structure Grammars, because it provides a semantically motivated linearized
analysis, by applying directly to superficial structures. Due to this characteristic,
STEMMA is particularly suitable to be integrated as a syntactic analyzer within
the text processing module in a speech synthesizer, to obtain in output isolated
phrasal components of the sentence, that can be associated directly with target
F0 curves (Pierrehumbert, 1981), for pitch contour stylization.
Fig. 5 Organization of stemmatic complements in STEMMA
Fig. 2 Spectrogram and F0 contour of the sentence
Finally, most POS taggers/parsers have been tested on only one or two
languages (AGFL, LTG for English; French: Bick, 2004; Portuguese: Bick, 1998),
whereas STEMMA performance has been preliminary verified on a controlled
corpus of sentences in 4 languages (French, English, Spanish and Danish),
showing 100 % accuracy with respect to the tested structural categories. The
system shows unresolved issues in classification of modal vs. manner aspects
of adverbs and of modal vs. qualitative aspects of adjectives in indo-european
languages; these ambiguities can be resolved by ad hoc manual tagging, but
they do not affect the intonational styles of the containing phrases.
L’artiste peint la nuit
(BLUE LINE Indicates intonational (F0) contour)
Fig. 6 Stemmatic representations of the dual interpretations the
sentences in Figg. 2-4: a. ‘the night’ = object= 3; b. ‘the night’ =
modal, temporal complement = 7
GOAL OF THE STUDY
The goal of the present work consists in testing the applicability of the stemmatic
model of semio-syntactic analysis, realized by Prof. Brandt, as part of the text
processing component of a Text-To-Speech synthesizer, to perform multilingual
semio-syntactic parsing, in order to automatically predict melodic contours for
speech synthesis.
DETECTION OF PROSODIC FEATURES
FOR SYNTACTIC-SEMANTIC
DISAMBIGUATION
Fig. 3 Spectrogram and F0 contour of the sentence
L’artista dipinge la notte
(BLUE LINE Indicates intonational (F0) contour)
Fig. 1 Configuration of a standard Text-To-Speech system
F(rom Sagisaka, Y. (1995) Spoken output technologies. In Cole, R., Mariani, S., Uszkoreit,
H., Zaenen, A. Zue, V. Survey of the state of the art in human languages technology. Center
for the Spoken Language Understanding, Oregon Graduate Institute, Beaverton, Oregon.
pp. 189-226 )
Fig. 4 Spectrogram and F0 contour of the sentence
El artista pinta la noche
(BLUE LINE Indicates intonational (F0) contour)
In this system, synthesis is attained not only by simulation of human speech by
generation of spectra and concatenation of speech segmental units (either
phonemes or diphones, to account for contextual effects), but also by simulation
of higher levels of linguistic processing (morphological, syntactic and semantic
parsing). This complex information, relative to the process of speech generation,
is encoded in rules, derived from phonetic theories and acoustic analyses, and
from theories of morphological, syntactic and semantic structure generation. This
technology is in fact, referred to as “speech synthesis by rule”.
SPEECH SYNTHESIS AND PROSODY
GENERATION
In speech synthesis, it is essential to control prosody, in order to assure
generation of natural sounding melodic patterns. Segmental duration control
is needed to model temporal characteristics (as tempo and rhythm) just as
fundamental frequency control is needed for control of tonal characteristics
(accent, intonation and stress). Duration control is generally implemented by
statistical models that can account for exceptions.
In order to generate an appropriate fundamental frequency (F0) contour,
based only on an input text, however, an intermediate prosodic structure
has to be specified, and text processing is needed, to produce this
intermediate prosodic structure, and to formulate the association rules
between phrasal components and relative intonation contours.
In order to obtain an accurate division in prosodic phrases, the text
processing component has to include at least a syntactic parser, which
derives syntactic groupings. Such groupings are usually associated with
prosodic phrases, but the two structures do not coincide exactly. Also, there
exist some structures which are not correctly parsed by a purely syntactic
analyzer, because they are inherently semantically ambiguous sentences;
such sentences allow two acceptable interpretations, but have a unique
superficial form like “L’artiste peint la nuit” (‘The artist paints the night/ or ‘in
the night’). The dual interpretation is disambiguated by intonation and
prosodic parameters, that differ across languages. Examples in Figg. 2-4
illustrate treatment of localized prosody on the sequence “paints the night”,
treated either as a direct object or a temporal construction, in French,
Spanish and Italian.
PROSODY AND SEMIO-SYNTACTIC PARSING
In this instance, the disambiguation is essential in order to select the appropriate intonation contour for
each of the two realizations of the sentences above. Although this is a pretty straightforward task for
humans, the selection of an appropriate intonation contour is an almost impossible task if performed
within a speech synthesizer, which does not include the sophisticated rules of semantic and syntactic
parsing used by human speakers.
Therefore, a better structural analysis of phrases in text sentences, especially if long and with little
punctuation, is needed, to approximate better the prosodic phrasing, from the structural grammatical
phrasing. In order to achieve this goal, semantic information needs to be introduced at the parsing
level. However, parsers that provide semantic/syntactic analysis exist only in rare experimental forms,
and are not used in commercial speech synthesis applications.
STEMMA
According to stemmatic syntax, a sentence is a grammatical construction, or it is a construction of
constructions, - where by construction we mean a string of words that ‘makes sense’ as a whole (more
precisely: a stable combination of Form and Meaning, or: of a composite Expression and a global
Content, or: of a Phonetic composition and a Semantic whole).
The fundamental problem for linguistics is that the Form of a construction must be linear, whereas the
Meaning of the same construction must be conceptual and therefore instantaneous and structured as a
mental icon.
The grammar of languages is the cognitive organ that articulates linearity and mental iconicity. It
structures the basic linguistic entities of sentences, the linguistic signs – essentially words and
morphemes – in such a way that the same signs participate in form and in meaning, since their signifiers
are phonetic elements, and their signifieds are semantic elements. The stemmatic syntactic model
describes grammar in this sense. It represents basic semantic operations of a construction – phrase or
sentence – as a cascade of operations of complementation preceded by an initial element, a ‘head’ that
serves as an anchoring reference for the operators (‘marks’) that determine the linear form of phrases
(constructions) and sentences (constructions of constructions).
The functionality of the STEMMA model as a generator of semantic
information for creation of rules to implement intonational features in
speech synthesis, has been tested. In particular, in the present study,
the possibility to predict correct intonation contours, based on
stemmatic analysis, to disambiguate the dual possible interpretation of
non marked syntactically ambiguous sentence sets, was verified.
Traditionally, such ambiguities are structurally analyzed in terms of
syntactic components: for example, sentences containing ambiguities
with respect to a prepositional phrase (PP) attachment, are categorized
based on the phrase modified by the PP: the dual interpretation is
assumed to derive from the fact that the PP can modify either the whole
verb phrase (VP), or only the noun phrase (NP) (e.g. “Demain je
t’ecrirais sans faute”; “He found the woman with the binoculars”;
Avesani, 1997). Previous studies comparing processes of
disambiguation in different languages on sentences with ambiguities on
PP, adverbial or relative attachments, or in scope of negation
(Hirschberg and Avesani, 1997), have shown that intonational phrasing
and nuclear stress variation are used consistently only to disambiguate
some semantic phenomena (e.g. different scope of ‘not’ negation, or
variation in focus on operators as ‘only’); on the other hand, ambiguous
attachment of prepositional phrases, adverbials, and relative clauses
was distinguished less consistently by phrasing and stress patterns by
speakers of different languages.
The present study has examined whether more consistent prosodic
patterns for disambiguation of PP and adverbial attachment sentences,
could be identified across languages and speakers, on the basis of
their stemmatic, as opposed to syntactic, structure. In particular, it was
tested whether some identifiable F0 patterns could be detected within
the domain of each stemmatic node differing in the two sentences, and
whether significant changes in the intonation pattern would take place
in correspondence of the head position; on the basis of these localized
robust patterns, it would be possible to extract rules to model prosody
across languages.
METHOD
The sentences have been pronounced by 2 English speakers, 2 Spanish, 2
Italian and 2 French speakers, in two separate repetitions. The speakers were
instructed to pronounce the sentences as if they were addressing an interlocutor.
The F0 contours have been extracted by Praat and labeled by the ToBI prosody
classification system (Silverman et al. 1992). Similarities and differences of the
contours for same phrases, corresponding to same nodes in stemmatic
Fig. 8 Spectrogram and F0 contour of the sentence
structure and to head positions, have been compared and analyzed, across
“I want you to be at the meeting”, and of the sentence “I am happy
speakers in the same language and across speakers in multiple languages.
that you will be at the meeting”, in different languages
RESULTS
Evidence for use of the same strategy by speakers of the same language has
been obtained; different strategies seem to be used across languages, e.g.
lowered F0 and insertion of pauses in French indicate presence of a modal
node rather than an object one, whereas Spanish and Italian, in our data, make
use of higher F0 on the temporal node with respect to the object one. However,
the use of these disambiguation criteria and parameters, is concentrated on the
position of the head corresponding to the ambiguous node, making it particularly
promising to search for systematic prosodic features occurring in concurrence
with specific stemmatic nodes.
PROSODIC FEATURES AND
SENTENCE MODES
(BLUE LINE Indicates intonational (F0) contour)
CONCLUSIONS
The results of the second study seem to support the
conclusion that variations in F0 contours might be used to
signal differences in stemmatic structure between two
sentences, but such variations cannot appear when only
sentence modality distinguishes two utterances.
These preliminary results seem to indicate that consideration
of semio-syntactic structure of a sentence can contribute to
extraction of natural rules for prosodic stylization to improve
naturalness and intelligibility of synthesized speech
A further experiment was conducted, testing whether a change in prosody is
accompanied to variation in modes of sentences (categorized as ‘volitive,
interrogative, assertive and affective’ in the STEMMA framework), in absence of
stemmatic structure change.
The fundamental role of (stemmatic) syntax is thus to let language combine linear (sequential) order and
conceptual (iconic) order into constructions with both phonetic and semantic properties. Prosodic
intonation of constructions can be considered as a phonetic indicator of specific syntactic structure;
differences in syntactic organization will correspond to different prosody. Prosody connects phonetics to
semantics, or semantics to phonetics, through grammar. In order to study the grammatical bridge
between phonetic form and semantic content, we need to model the elementary grammatical
organization of sentences and their parts; the stemmatic model has been developed in a comparative
perspective to reflect the general structural properties of grammar across languages. Proximity of
linguistic signs that participate in a meaningful whole, or part of whole, does not imply direct contact (cf.
discontinuous complements), but it does imply sequential preferences. It turns out that stemmatic syntax
can account for both afferent (form –> meaning) and efferent (meaning –> form) processes.
Stemmatic syntax describes sentences as cascades of complement nodes, or grammatical connectors
that integrate relations between verbs, subjects, predicates, objects, indirect objects, adverbials of
different kinds, and syntactic embeddings. It represents the ‘logic’ of syntax as a simplified ‘school
grammar’, with a simplified semantics of cases and prepositional phrases to be specified for each
language.
Stemmatic representations of the sentences “I want / I wonder / I know / I
I am happy / that you will be at the meeting” in different languages,
corresponding respectively to ‘volitive, interrogative, assertive and affective’
sentence modes
Fig. 7