Effects of Surprisal and Entropy on Vowel Duration in Japanese

The interaction between predictability and pre-boundary lengthening on syllable duration in Taiwan Southern Min

This study investigated how predictability and prosodic phrasing interact in accounting for the variability of syllable duration in Taiwan Southern Min. Speech data were extracted from 8 hours of spontaneous speech. Three predictability measurements were examined: bigram surprisal, bigram informativity, and lexical frequency. Results showed that higher informativity and surprisal led to longer syllables. As for the interaction with prosodic positions, there was a general weakening of predictability effects for syllables closer to the boundary, especially in the pre-boundary position, where pre-boundary lengthening was the strongest. However, the effect of word informativity appeared to be least modulated by this effect of boundary marking. These findings are consistent with a hypothesis that prosodic structure modulates the predictability effects on phonetic variability. The robustness of informativity in predicting syllable duration also suggests a possibility of stored phonetic variants associated with a word's usual contextual predictability.

More on the articulation of devoiced [u] in Tokyo Japanese: effects of surrounding consonants

Past work investigating the lingual articulation of devoiced vowels in Tokyo Japanese has revealed optional but categorical deletion. Some devoiced vowels retained a full lingual target, just like their voiced counterparts, whereas others showed trajectories that are best modelled as targetless, i.e., linear interpolation between the surrounding vowels. The current study explored the hypothesis that this probabilistic deletion is modulated by the identity of the surrounding consonants. A new EMA experiment with an extended stimulus set replicates the core finding of Shaw, Jason & Shigeto Kawahara. 2018b. The lingual gesture of devoiced [u] in Japanese. Journal of Phonetics 66. 100-119. DOI:https://doi.org/10.1016/j.wocn.2017.09.007 that Japanese devoiced [u] sometimes lacks a tongue body raising gesture. The current results moreover show that surrounding consonants do indeed affect the probability of tongue dorsum targetlessness. We found that deletion of devoiced vowels is affected by the place of articulation of the preceding consonant; deletion is more likely following a coronal fricative than a labial fricative. Additionally, we found that the manner combination of the flanking consonants, fricative-fricative versus fricative-stop, also has an effect, at least for some speakers; however, unlike the effect of C1 place, the direction of the manner combination effect varies across speakers with some deleting more often in fricative-stop environments and others more often in fricative-fricative environments.

Multiple Sources of Surprisal Affect Illusory Vowel Epenthesis

Illusory epenthesis is a phenomenon in which listeners report hearing a vowel between a phonotactically illegal consonant cluster, even in the complete absence of vocalic cues. The present study uses Japanese as a test case and investigates the respective roles of three mechanisms that have been claimed to drive the choice of epenthetic vowel-phonetic minimality, phonotactic predictability, and phonological alternations-and propose that they share the same rational goal of searching for the vowel that minimally alters the original speech signal. Additionally, crucial assumptions regarding phonological knowledge held by previous studies are tested in a series of corpus analyses using the Corpus of Spontaneous Japanese. Results show that all three mechanisms can only partially account for epenthesis patterns observed in language users, and the study concludes by discussing possible ways in which the mechanisms might be integrated.

Japanese Perceptual Epenthesis is Modulated by Transitional Probability

Perceptual epenthesis is the perception of illusory vowels in consonantal sequences that violate native phonotactics. The consensus has been that each language has a single, predictable candidate for perceptual epenthesis, that vowel which is most minimal (i.e., shortest and/or quietest). However, recent studies have shown that alternate epenthetic vowels can be perceived when the perceptual epenthesis of the minimal vowel would violate native co-occurrence restrictions. We propose a potential explanation for these observed patterns: speech perception, and thus also vowel perceptual epenthesis, is modulated by transitional probability whereby epenthetic vowels must conform to the language specific expectations of the listener. To test this explanation, we present two experiments examining perceptual epenthesis of two Japanese vowels-/u/ and /i/-against their transitional probability in CV sequences. In Experiment 1, Japanese listeners assigned VCCV tokens to VCuCV and VCiCV categories. In Experiment 2, participants discriminated VCCV tokens from VCuCV and VCiCV tokens. The results show that sequences where /i/ is transitionally probable are more likely to elicit /i/ perceptual epenthesis.

Prosody leaks into the memories of words

The average predictability (aka informativity) of a word in context has been shown to condition word duration (Seyfarth, 2014). All else being equal, words that tend to occur in more predictable environments are shorter than words that tend to occur in less predictable environments. One account of the informativity effect on duration is that the acoustic details of probabilistic reduction are stored as part of a word's mental representation. Other research has argued that predictability effects are tied to prosodic structure in integral ways. With the aim of assessing a potential prosodic basis for informativity effects in speech production, this study extends past work in two directions; it investigated informativity effects in another large language, Mandarin Chinese, and broadened the study beyond word duration to additional acoustic dimensions, pitch and intensity, known to index prosodic prominence. The acoustic information of content words was extracted from a large telephone conversation speech corpus with over 400,000 tokens and 6000 word types spoken by 1655 individuals and analyzed for the effect of informativity using frequency statistics estimated from a 431 million word subtitle corpus. Results indicated that words with low informativity have shorter durations, replicating the effect found in English. In addition, informativity had significant effects on maximum pitch and intensity, two phonetic dimensions related to prosodic prominence. Extending this interpretation, these results suggest that predictability is closely linked to prosodic prominence, and that the lexical representation of a word includes phonetic details associated with its average prosodic prominence in discourse. In other words, the lexicon absorbs prosodic influences on speech production.

Linguistic Laws in Speech: The Case of Catalan and Spanish

In this work we consider Glissando Corpus—an oral corpus of Catalan and Spanish—and empirically analyze the presence of the four classical linguistic laws (Zipf’s law, Herdan’s law, Brevity law, and Menzerath–Altmann’s law) in oral communication, and further complement this with the analysis of two recently formulated laws: lognormality law and size-rank law. By aligning the acoustic signal of speech production with the speech transcriptions, we are able to measure and compare the agreement of each of these laws when measured in both physical and symbolic units. Our results show that these six laws are recovered in both languages but considerably more emphatically so when these are examined in physical units, hence reinforcing the so-called ‘physical hypothesis’ according to which linguistic laws might indeed have a physical origin and the patterns recovered in written texts would, therefore, be just a byproduct of the regularities already present in the acoustic signals of oral communication.

On the physical origin of linguistic laws and lognormality in speech

Physical manifestations of linguistic units include sources of variability due to factors of speech production which are by definition excluded from counts of linguistic symbols. In this work, we examine whether linguistic laws hold with respect to the physical manifestations of linguistic units in spoken English. The data we analyse come from a phonetically transcribed database of acoustic recordings of spontaneous speech known as the Buckeye Speech corpus. First, we verify with unprecedented accuracy that acoustically transcribed durations of linguistic units at several scales comply with a lognormal distribution, and we quantitatively justify this 'lognormality law' using a stochastic generative model. Second, we explore the four classical linguistic laws (Zipf's Law, Herdan's Law, Brevity Law and Menzerath-Altmann's Law (MAL)) in oral communication, both in physical units and in symbolic units measured in the speech transcriptions, and find that the validity of these laws is typically stronger when using physical units than in their symbolic counterpart. Additional results include (i) coining a Herdan's Law in physical units, (ii) a precise mathematical formulation of Brevity Law, which we show to be connected to optimal compression principles in information theory and allows to formulate and validate yet another law which we call the size-rank law or (iii) a mathematical derivation of MAL which also highlights an additional regime where the law is inverted. Altogether, these results support the hypothesis that statistical laws in language have a physical origin.

Durational Evidence That Tokyo Japanese Vowel Devoicing Is Not Gradient Reduction

A central question in the Japanese high vowel devoicing literature concerns whether vowels are devoiced through a categorical process or via gradient reduction. Examining how vowel height and consonantal voicing condition phrase-internal CV duration in a corpus of spontaneous Tokyo Japanese, it was found that CVs containing high vowels are substantially shorter before voiceless consonants, whilst non-high vowels do not exhibit comparable shortening. This quantitative difference between CV durations suggests a controlled temporal compression of the CV, consistent with views that Japanese vowel devoicing is produced through a categorical process targeting high vowels preceding voiceless consonants, and supports previous observations made of elicited productions.

Contextual predictability influences word and morpheme duration in a morphologically complex language (Kaqchikel Mayan)

The probability is one of the many factors which influence phonetic variation. Contextual probability, which describes how predictable a linguistic unit is in some local environment, has been consistently shown to modulate the phonetic salience of words and other linguistic units in speech production (the probabilistic reduction effect). In this paper the question of whether the probabilistic reduction effect, as previously observed for majority languages like English, is also found in a language (Kaqchikel Mayan) which has relatively rich morphology is explored. Specifically, whether the contextual predictability of words and morphemes influences their phonetic duration in Kaqchikel is examined. It is found that the contextual predictability of a word has a significant effect on its duration. The effect is manifested differently for lexical words and function words. It is also found that the contextual predictability of certain prefixes in Kaqchikel affects their duration, showing that contextual predictability may drive reduction effects at multiple levels of structure. While the findings are broadly consistent with many previous studies (primarily on English), some of the details of the results are different. These differences highlight the importance of examining the probabilistic reduction effect in languages beyond the majority, Indo-European languages most commonly investigated in experimental and corpus linguistics.

Recoverability-driven coarticulation: Acoustic evidence from Japanese high vowel devoicing

High vowel devoicing in Japanese, where /i, u/ in a C₁VC₂ sequence devoice when both C₁ and C₂ are voiceless, has been studied extensively, but factors that contribute to the devoiced vowels' likelihood of complete deletion is still debated. This study examines the effects of phonotactic predictability on the deletion of devoiced vowels. Native Tokyo Japanese speakers (N = 22) were recorded in a sound-attenuated booth reading sentences containing lexical stimuli. C₁ of the stimuli were /k, ʃ/, after which either high vowel can occur, and /ʧ, ϕ, s, ç/, after which only one of the two occurs. C₂ was always a stop. C₁ duration and center of gravity (COG), the amplitude weighted mean of frequencies present in a signal, were measured. Duration results show that devoicing lengthens only non-fricatives, while it has either no effect or a shortening effect on fricatives. COG results show that coarticulatory effects of devoiced vowels are evident in /k, ʃ/ but not in /ʧ, ϕ, s, ç/. Devoiced high vowels, therefore, seem to be more likely to delete when the vowel is phonotactically predictable than when it is unpredictable.

Durational compensation within a CV mora in spontaneous Japanese: Evidence from the Corpus of Spontaneous Japanese

Previous experimental studies showed that in Japanese, vowels are longer after shorter onset consonants; there is durational compensation within a CV-mora. In order to address whether this compensation occurs in natural speech, this study re-examines this observation using the Corpus of Spontaneous Japanese. The results, which are based on more than 200 000 CV-mora tokens, show that there is a negative correlation between the onset consonant and the following vowel in terms of their duration. The statistical significance of this negative correlation is assessed by a traditional correlation analysis as well as a bootstrap resampling analysis, which both show that it is unlikely that the observed compensation effect occurred by chance. The compensation is not perfect, however, suggesting that it is a stochastic tendency rather than an absolute principle. This paper closes with a discussion of potential factors that may interact with the durational compensation effect.