Publications

Abstract

Acoustic reduction refers to the frequent phenomenon in conversational speech that words are produced with fewer or lenited segments compared to their citation forms. The few published studies on the production and comprehension of acoustic reduction have important implications for the debate on the relevance of abstractions and exemplars in speech processing. This article discusses these implications. It first briefly introduces the key assumptions of simple abstractionist and simple exemplar-based models. It then discusses the literature on acoustic reduction and draws the conclusion that both types of models need to be extended to explain all findings. The ultimate model should allow for the storage of different pronunciation variants, but also reserve an important role for phonetic implementation. Furthermore, the recognition of a highly reduced pronunciation variant requires top down information and leads to activation of the corresponding unreduced variant, the variant that reaches listeners’ consciousness. These findings are best accounted for in hybrids models, assuming both abstract representations and exemplars. None of the hybrid models formulated so far can account for all data on reduced speech and we need further research for obtaining detailed insight into how speakers produce and listeners comprehend reduced speech.

Abstract

This article introduces a new speech corpus, the Nijmegen Corpus of Casual Czech (NCCCz), which contains more than 30 hours of high-quality recordings of casual conversations in Common Czech, among ten groups of three male and ten groups of three female friends. All speakers were native speakers of Czech, raised in Prague or in the region of Central Bohemia, and were between 19 and 26 years old. Every group of speakers consisted of one confederate, who was instructed to keep the conversations lively, and two speakers naive to the purposes of the recordings. The naive speakers were engaged in conversations for approximately 90 minutes, while the confederate joined them for approximately the last 72 minutes. The corpus was orthographically annotated by experienced transcribers and this orthographic transcription was aligned with the speech signal. In addition, the conversations were videotaped. This corpus can form the basis for all types of research on casual conversations in Czech, including phonetic research and research on how to improve automatic speech recognition. The corpus will be freely available

Abstract

In spontaneous conversations between adults, words are often pronounced with fewer segments or syllables than their citation forms. The question arises whether infant-directed speech also contains phonetic reduction. If so, infants would be presented with speech input that enables them to acquire reduced variants from an early age. This study compared speech directed at 11- and 12-month-old infants with adult-directed conversational speech and adult-directed read speech. In an acoustic study, 216 tokens of the Dutch words allemaal and helemaal from speech corpora were analyzed for duration, number of syllables, and vowel quality. In a perception study, adult participants rated these same materials for reduction and provided phonetic transcriptions. The results show that these two words are frequently reduced in infant-directed speech, and that their degree of reduction is comparable with conversational adult-directed speech. These findings suggest that lexical representations for reduced pronunciation variants can be acquired early in linguistic development

Abstract

This paper describes the pilot study of phonetic segmentation applied to Nijmegen Corpus of Casual Czech (NCCCz). This corpus contains informal speech of strong spontaneous nature which influences the character of produced speech at various levels. This work is the part of wider research related to the analysis of pronunciation reduction in such informal speech. We present the analysis of the accuracy of phonetic segmentation when canonical or reduced pronunciation is used. The achieved accuracy of realized phonetic segmentation provides information about general accuracy of proper acoustic modelling which is supposed to be applied in spontaneous speech recognition. As a byproduct of presented spontaneous speech segmentation, this paper also describes the created lexicon with canonical pronunciations of words in NCCCz, a tool supporting pronunciation check of lexicon items, and finally also a minidatabase of selected utterances from NCCCz manually labelled on phonetic level suitable for evaluation purposes

Abstract

This study examines how lexical frequency and planning problems can predict phonetic variability in the function word ‘the’ in conversational speech produced by non-native speakers of English. We examined 3180 tokens of ‘the’ drawn from English conversations between native speakers of Czech or Norwegian. Using regression models, we investigated the effect of following word frequency and disfluencies on three phonetic parameters: vowel duration, vowel quality, and consonant quality. Overall, the non-native speakers showed variation that is very similar to the variation displayed by native speakers of English. Like native speakers, Czech speakers showed an effect of frequency on vowel durations, which were shorter in more frequent word sequences. Both groups of speakers showed an effect of frequency on consonant quality: the substitution of another consonant for /ð/ occurred more often in the context of more frequent words. The speakers in this study also showed a native-like allophonic distinction in vowel quality, in which /ði/ occurs more often before vowels and /ðə/ before consonants. Vowel durations were longer in the presence of following disfluencies, again mirroring patterns in native speakers, and the consonant quality was more likely to be the target /ð/ before disfluencies, as opposed to a different consonant. The fact that non-native speakers show native-like sensitivity to lexical frequency and disfluencies suggests that these effects are consequences of a general, non-language-specific production mechanism governing language planning. On the other hand, the non-native speakers in this study did not show native-like patterns of vowel quality in the presence of disfluencies, suggesting that the pattern attested in native speakers of English may result from language-specific processes separate from the general production mechanisms

Abstract

This paper addresses the question how to compare reaction times computed by a computational model of speech comprehension with observed reaction times by participants. The question is based on the observation that reaction time sequences substantially differ per participant, which raises the issue of how exactly the model is to be assessed. Part of the variation in reaction time sequences is caused by the so-called local speed: the current reaction time correlates to some extent with a number of previous reaction times, due to slowly varying variations in attention, fatigue etc. This paper proposes a method, based on time series analysis, to filter the observed reaction times in order to separate the local speed effects. Results show that after such filtering the between-participant correlations increase as well as the average correlation between participant and model increases. The presented technique provides insights into relevant aspects that are to be taken into account when comparing reaction time sequences

Abstract

This study investigated whether a shadowing task can provide insights in the nature of reduction processes that are typical of casual speech. We focused on the shortening and presence versus absence of schwa and /t/ in Dutch past participles. Results showed that the absence of these segments was affected by the same variables as their shortening, suggesting that absence mostly resulted from extreme gradient shortening. This contrasts with results based on recordings of spontaneous conversations. We hypothesize that this difference is due to non-casual fast speech elicited by a shadowing task.

Abstract

This paper examines the role of morphological structure in the reduced pronunciation of morphologically complex words by discussing and re-analyzing data from the literature. Acoustic reduction refers to the phenomenon that, in spontaneous speech, phonemes may be shorter or absent. We review studies investigating effects of the repetition of a morpheme, of whether a segment plays a crucial role in the identification of its morpheme, and of a word's morphological decomposability. We conclude that these studies report either no effects of morphological structure or effects that are open to alternative interpretations. Our analysis also reveals the need for a uniform definition of morphological decomposability. Furthermore, we examine whether the reduction of segments in morphologically complex words correlates with these segments' contribution to the identification of the whole word, and discuss previous studies and new analyses supporting this hypothesis. We conclude that the data show no convincing evidence that morphological structure conditions reduction, which contrasts with the expectations of several models of speech production and of morphological processing (e.g., weaver++ and dual-route models). The data collected so far support psycholinguistic models which assume that all morphologically complex words are processed as complete units.

Abstract

This paper investigates the realization of word-final /t/ in conversational standard Dutch. First, based on a large number of word tokens (6747) annotated with broad phonetic transcription by an automatic transcription tool, we show that morphological properties of the words and their position in the utterance's syntactic structure play a role for the presence versus absence of their final /t/. We also replicate earlier findings on the role of predictability (word frequency and bigram frequency with the following word) and provide a detailed analysis of the role of segmental context. Second, we analyze the detailed acoustic properties of word-final /t/ on the basis of a smaller number of tokens (486) which were annotated manually. Our data show that word and bigram frequency as well as segmental context also predict the presence of sub-phonemic properties. The investigations presented in this paper extend research on the realization of /t/ in spontaneous speech and have potential consequences for psycholinguistic models of speech production and perception as well as for automatic speech recognition systems.

Abstract

In spontaneous speech, words may be realised shorter than in formal speech (e.g., English yesterday may be pronounced like [jɛʃeɩ]). Previous research has shown that context is required to understand highly reduced pronunciation variants. We investigated the extent to which listeners can predict low predictability reduced words on the basis of the semantic/syntactic and acoustic cues in their context. In four experiments, participants were presented with either the preceding context or the preceding and following context of reduced words, and either heard these fragments of conversational speech, or read their orthographic transcriptions. Participants were asked to predict the missing reduced word on the basis of the context alone, choosing from four plausible options. Participants made use of acoustic cues in the context, although casual speech typically has a high speech rate, and acoustic cues are much more unclear than in careful speech. Moreover, they relied on semantic/syntactic cues. Whenever there was a conflict between acoustic and semantic/syntactic contextual cues, measured as the word's probability given the surrounding words, listeners relied more heavily on acoustic cues. Further, context appeared generally insufficient to predict the reduced words, underpinning the significance of the acoustic characteristics of the reduced words themselves.

Abstract

This paper presents a corpus study that investigates the co-occurrence of reduced word forms in natural speech. We extracted Dutch past participles from three different speech registers and investigated the influence of several predictor variables on the presence and duration of schwas in prefixes and /t/s in suffixes. Our results suggest that reduced word forms tend to co-occur even if we partial out the effect of speech rate. The implications of our findings for episodic and abstractionist models of lexical representation are discussed.

Abstract

This paper discusses four experiments on Dutch which show that distinctive phonological features differ in their relevance for word recognition. The relevance of a feature for word recognition depends on its phonological stability, that is, the extent to which that feature is generally realized in accordance with its lexical specification in the relevant word position. If one feature value is uninformative, all values of that feature are less relevant for word recognition, with the least informative feature being the least relevant. Features differ in their relevance both in spoken and written word recognition, though the differences are more pronounced in auditory lexical decision than in self-paced reading.

Abstract

This study addresses the question to what extent the production of regular past tense forms in Dutch is a¤ected by analogical processes. We report an experiment in which native speakers of Dutch listened to existing regular verbs over headphones, and had to indicate which of the past tense allomorphs, te or de, was appropriate for these verbs. According to generative analyses, the choice between the two su‰xes is completely regular and governed by the underlying [voice]-specification of the stem-final segment. In this approach, no analogical e¤ects are expected. In connectionist and analogical approaches, by contrast, the phonological similarity structure in the lexicon is expected to a¤ect lexical processing. Our experimental results support the latter approach: all participants created more nonstandard past tense forms, produced more inconsistency errors, and responded more slowly for verbs with stronger analogical support for the nonstandard form.

Abstract

Listeners cannot recognize highly reduced word forms in isolation, but they can do so when these forms are presented in context (Ernestus, Baayen, & Schreuder, 2002). This suggests that not all possible surface forms of words have equal status in the mental lexicon. The present study shows that the reduced forms are linked to the canonical representations in the mental lexicon, and that these latter representations induce reconstruction processes. Listeners restore suffixes that are partly or completely missing in reduced word forms. A series of phoneme-monitoring experiments reveals the nature of this restoration: the basis for suffix restoration is mainly phonological in nature, but orthography has an influence as well.

Abstract

In this paper, we show that both token and type-based effects in lexical processing can result from a single, token-based, system, and therefore, do not necessarily reflect different levels of processing. We report three Simple Recurrent Networks modeling Dutch past-tense formation. These networks show token-based frequency effects and type-based analogical effects closely matching the behavior of human participants when producing past-tense forms for both existing verbs and pseudo-verbs. The third network covers the full vocabulary of Dutch, without imposing predefined linguistic structure on the input or output words.

Abstract

This paper discusses some pitfalls in corpus research and suggests solutions on the basis of examples and computer simulations. We first address reliability problems in language transcriptions, agreement between transcribers, and how disagreements can be dealt with. We then show that the frequencies of occurrence obtained from a corpus cannot always be analyzed with the traditional X2 test, as corpus data are often not sequentially independent and unit independent. Next, we stress the relevance of the power of statistical tests, and the sizes of statistically significant effects. Finally, we point out that a t-test based on log odds often provides a better alternative to a X2 analysis based on frequency counts.