Patti Price

Segmental durations in the vicinity of prosodic phrase boundaries

Numerous studies have indicated that prosodic phrase boundaries may be marked by a variety of acoustic phenomena including segmental lengthening. It has not been established, however, whether this lengthening is restricted to the immediate vicinity of the boundary, or if it extends over some larger region. In this study, segmental lengthening in the vicinity of prosodic boundaries is examined and found to be restricted to the rhyme of the syllable preceding the boundary. By using a normalized measure of segmental lengthening, and by compensating for differences in speaking rate, it is also shown that at least four distinct types of boundaries can be distinguished on the basis of this lengthening.

The use of prosody in syntactic disambiguation

Prosodic structure and syntactic structure are not identical; neither are they unrelated. Knowing when and how the two correspond could yield better quality speech synthesis, could aid in the disambiguation of competing syntactic hypotheses in speech understanding, and could lead to a more comprehensive view of human speech processing. In a set of experiments involving 35 pairs of phonetically similar sentences representing seven types of structural contrasts, the perceptual evidence shows that some, but not all, of the pairs can be disambiguated on the basis of prosodic differences. The phonological evidence relates the disambiguation primarily to boundary phenomena, although prominences sometimes play a role. Finally, phonetic analyses describing the attributes of these phonological markers indicate the importance of both absolute and relative measures.

The DARPA 1000-word resource management database for continuous speech recognition

A database of continuous read speech has been designed and recorded within the DARPA strategic computing speech recognition program. The data is intended for use in designing and evaluating algorithms for speaker-independent, speaker-adaptive and speaker-dependent speech recognition. The data consists of read sentences appropriate to a naval resource management task built around existing interactive database and graphics programs. The 1000-word task vocabulary is intended to be logically complete and habitable. The database, which represents over 21000 recorded utterances from 160 talkers with a variety of dialects, includes a partition of sentences and talkers for training and for testing purposes.<<ETX>>

The challenge of spoken language systems: Research directions for the nineties

A spoken language system combines speech recognition, natural language processing and human interface technology. It functions by recognizing the persons words, interpreting the sequence of words to obtain a meaning in terms of the application, and providing an appropriate response back to the user. Potential applications of spoken language systems range from simple tasks, such as retrieving information from an existing database (traffic reports, airline schedules), to interactive problem solving tasks involving complex planning and reasoning (travel planning, traffic routing), to support for multilingual interactions. We examine eight key areas in which basic research is needed to produce spoken language systems: (1) robust speech recognition; (2) automatic training and adaptation; (3) spontaneous speech; (4) dialogue models; (5) natural language response generation; (6) speech synthesis and speech generation; (7) multilingual systems; and (8) interactive multimodal systems. In each area, we identify key research challenges, the infrastructure needed to support research, and the expected benefits. We conclude by reviewing the need for multidisciplinary research, for development of shared corpora and related resources, for computational support and far rapid communication among researchers. The successful development of this technology will increase accessibility of computers to a wide range of users, will facilitate multinational communication and trade, and will create new research specialties and jobs in this rapidly expanding area. >

Automatic text-independent pronunciation scoring of foreign language student speech

SRI International is currently involved in the development of a new generation of software systems for automatic scoring of pronunciation as part of the Voice Interactive Language Training System (VILTS) project. This paper describes the goals of the VILTS system, the speech corpus and the algorithm development. The automatic grading system uses SRIs Decipher/sup TM/ continuous speech recognition system to generate phonetic segmentations that are used to produce pronunciation scores at the end of each lesson. The scores produced by the system are similar to those of expert human listeners. Unlike previous approaches, in which models were built for specific sentences or phrases, we present a new family of algorithms designed to perform well even when knowledge of the exact text to be used is not available.

Combining knowledge sources to reorder N-best speech hypothesis lists

A simple and general method is described that can combine different knowledge sources to reorder N-best lists of hypotheses produced by a speech recognizer. The method is automatically trainable, acquiring information from both positive and negative examples. In experiments, the method was tested on a 1000-utterance sample of unseen ATIS data.

Human-machine problem solving using spoken language systems (SLS): factors affecting performance and user satisfaction

We have analyzed three factors affecting user satisfaction and system performance using an SLS implemented in the ATIS domain. We have found that: (1) trade-offs between speed and accuracy have different implications for user satisfaction; (2) recognition performance improves over time, at least in part because of a reduction in sentence perplexity; and (3) hyperarticulation increases recognition errors, and while instructions can reduce this behavior, they do not result in improved recognition performance. We conclude that while users may adapt to some aspects of an SLS, certain types of user behavior may require technological solutions.

Linguistic constraints in hidden Markov model based speech recognition

A speaker-independent, continuous-speech, large-vocabulary speech recognition system, DECIPHER, has been developed. It provides state-of-the-art performance on the DARPA standard speaker-independent resource management training and testing materials. The approach is to integrate speech and linguistic knowledge into the HMM (hidden Markov model) framework. Performance improvements arising from detailed phonological modeling and from the incorporation of cross-word coarticulatory constraints are described. It is concluded that speech and linguistic knowledge sources can be used to improve the performance of HMM-based speech recognition systems provided that care is taken to incorporate these knowledge sources appropriately.<<ETX>>

Spontaneous speech effects in large vocabulary speech recognition applications

We describe three analyses on the effects of spontaneous speech on continuous speech recognition performance. We have found that: (1) spontaneous speech effects significantly degrade recognition performance, (2) fluent spontaneous speech yields word accuracies equivalent to read speech, and (3) using spontaneous speech training data can significantly improve performance for recognizing spontaneous speech. We conclude that word accuracy can be improved by explicitly modeling spontaneous effects in the recognizer, and by using as much spontaneous speech training data as possible. Inclusion of read speech training data, even within the task domain, does not significantly improve performance.

Male and female voice source characteristics: Inverse filtering results

Abstract Detailed data on voicing source characteristics are of interest in both analysis and synthesis of speech. In this study, a time-domain based method of inverse filtering was used to analyze male and female utterances produced with several voice qualities. Fourteen mono-syllabic utterances (ten in normal voicing style, and 2 each in creaky and breathy voice) by each of 8 speakers (4 men, 4 women) were filtered by a set of zero pairs corresponding to the measured formants. The resulting differentiated flow waveforms were analyzed in the time domain and in the frequency domain at voicing onset, near the middle of the vowel, and near the end of voicing. Though there was variability among subjects of the same sex, the women tended to have shorter closed quotients and longer return quotients (the period between maximal rate of change of flow and minimal flow). In the spectral domain, there tended to be less energy at higher frequencies in the middle of the vowel for the women compared to the men. The magnitudes of the male-female differences are similar to those observed for the creaky-normal voicing differences and breathy-normal differences. These differences may arise from a combination of biological, sociological and acoustical effects.