Phonetics

Statistical distributions of consonant variants in infant-directed speech: Evidence that /t/ may be exceptional Publication date: July 2019 Source: Journal of Phonetics, Volume 75 Author(s): Laura Dilley, Jessica Gamache, Yuanyuan Wang, Derek M. Houston, Tonya R. Bergeson Abstract Statistical distributions of phonetic variants in spoken language influence speech perception for both language learners and mature users. We theorized that patterns of phonetic variant processing of consonants demonstrated by adults might stem in part from patterns of early exposure to statistics of phonetic variants in infant-directed (ID) speech. In particular, we hypothesized that ID speech might involve greater proportions of canonical /t/ pronunciations compared to adult-directed (AD) speech in at least some phonological contexts. This possibility was tested using a corpus of spontaneous speech of mothers speaking to other adults, or to their typically-developing infant. Tokens of word-final alveolar stops – including /t/, /d/, and the nasal stop /n/ – were examined in assimilable contexts (i.e., those followed by a word-initial labial and/or velar); these were classified as canonical, assimilated, deleted, or glottalized. Results confirmed that there were significantly more canonical pronunciations in assimilable contexts in ID compared with AD speech, an effect which was driven by the phoneme /t/. These findings suggest that at least in phonological contexts involving possible assimilation, children are exposed to more canonical /t/ variant pronunciations than adults are. This raises the possibility that perceptual processing of canonical /t/ may be partly attributable to exposure to canonical /t/ variants in ID speech. Results support the need for further research into how statistics of variant pronunciations in early language input may shape speech processing across the lifespan.

Spontaneous nasalization after glottal consonants in Thai Publication date: July 2019 Source: Journal of Phonetics, Volume 75 Author(s): Sarah E. Johnson, Marissa Barlaz, Ryan K. Shosted, Brad P. Sutton Abstract Spontaneous nasalization is the emergence of distinctive nasalization in contexts lacking an historical etymological nasal. In Thai, low and mid-low vowels nasalize after /h/ and to a lesser degree after /ʔ/. It has been reasoned that nasalization after /h/ may occur because breathiness and nasalization are acoustically similar; both introduce higher energy at low frequencies and increase spectral tilt. Glottal consonants may generally facilitate nasalization because aerodynamically they do not require velopharyngeal closure. We investigated velopharyngeal opening (VPO) during vowels after /h/ and/ ʔ/ and measured spectral tilt (H1–H2). We measured VPO by processing oblique ultra-fast magnetic resonance images of the velopharyngeal port. Four Thai speakers exhibited a complex system of VPO that varied based on vowel height and preceding consonant. Low vowels after /h/ manifested more physiological nasalization than low vowels after /ʔ/, while the former were often produced with higher spectral tilt, which may be indicative of either increased breathiness or nasalization. While VPO is likely responsible for impressions of greater nasalization after /h/, our findings suggest that breathiness and VPO may interact in the spontaneously nasalized vowels of Thai.

Influence of coda stop features on perceived vowel duration Publication date: July 2019 Source: Journal of Phonetics, Volume 75 Author(s): Chelsea Sanker Abstract Four experiments tested what cues contribute to English speakers' perception of vowel duration. Listeners categorized the duration of vowels as 'long' or 'short' for stimuli produced with voiced, voiceless, breathy voiced, or voiceless aspirated stop codas. Listeners demonstrated a strong ability to perceive vowel duration, though perception was continuous rather than categorical. There were several interacting factors influencing perceived vowel duration, based on expectations set by the presence of particular codas and also acoustic effects of the coda on the vowel. When the coda was removed, vowels that had been produced before voiced codas were perceived as longer than vowels produced before voiceless codas, though they exhibited the opposite effect when codas were present. Vowels were also perceived as longer when produced before breathy voiced stops, regardless of whether or not the stop was present. The steeper f0 falls associated with voiced codas within these stimuli likely contributed to the longer perceived duration of vowels from this environment; manipulating f0 contours eliminated effects of the original coda on perceived vowel duration. The effects of the production environment on perceived vowel duration suggest a possible perceptual pathway for the voicing effect on vowel duration.

Cue-shifting between acoustic cues: Evidence for directional asymmetry Publication date: July 2019 Source: Journal of Phonetics, Volume 75 Author(s): Meng Yang, Megha Sundara Abstract Previous research shows that experience with co-varying cues is neither sufficient nor necessary for listeners to integrate them perceptually. Auditory Enhancement theorists explain this by positing that listeners integrate two cues more readily if the cues enhance each other's percept. To isolate the role of enhancement from that of experience, we forced English adult listeners to shift attention between two enhancing cues that they do not use phonemically, pitch and breathiness, by reversing the informativeness of the two cues in a cue weighting experiment. Listeners were able to shift attention from pitch to breathiness and vice versa if the two cues were in an enhancing relation. When this relationship was reversed, listeners could shift attention from pitch to breathiness but not in the opposite direction. Clearly, both the change in informativeness and the enhancing properties of the cues influenced the listeners' re-weighting of these cues. However, the directional asymmetry was not predicted. Moreover, the same asymmetry was observed in two new groups of listeners who have native language experience with either pitch or breathiness. We discuss the consequences of such asymmetric enhancement effects, rising from either processing limitations or articulatory contingencies, for language change.

Formant dynamics of Spanish vocalic sequences in related speakers: A forensic-voice-comparison investigation Publication date: July 2019 Source: Journal of Phonetics, Volume 75 Author(s): Eugenia San Segundo, Junjie Yang Abstract This study investigates the dynamic acoustic properties of 19 vocalic sequences of Standard Peninsular Spanish, showing their potential for forensic voice comparison. Parametric curves (polynomials and discrete cosine transform) were fitted to the formant trajectories of the 19 Spanish vocalic sequences of 54 male speakers, comprising monozygotic (MZ) and dizygotic (DZ) twin pairs, non-twin brothers and unrelated speakers. Using the curve-fitting estimated coefficients as input to a multivariate-kernel-density formula, cross-validated likelihood ratios were calculated to express the probability of obtaining the observed difference between two speech samples under the hypothesis that the samples were produced by the same speaker and under the hypothesis that they were produced by a different speaker. The results show that the best-performing system is one that fuses the 19 vocalic sequences with a geometric-mean fusion method. When challenging the system with related speakers, the results show that MZ twin pairs affect performance but, more importantly, that non-twin sibling pairs can deteriorate performance too. This suggests that more investigations are necessary into a range of similar-sounding speakers beyond MZ twins. Several nurture aspects are highlighted as explanatory factors for the strikingly high similarity of a specific non-twin sibling pair.

Alignment of f0 peak in different pitch accent types affects perception of metrical stress Publication date: May 2019 Source: Journal of Phonetics, Volume 74 Author(s): Katharina Zahner, Sophie Kutscheid, Bettina Braun Abstract In intonation languages, pitch accents are associated with stressed syllables, therefore accentuation is a sufficient cue to the position of metrical stress in perception. This paper investigates how stress perception in German is affected by different pitch accent types (with different f0 alignments). Experiment 1 showed more errors in stress identification when f0 peaks and stressed syllables were not aligned – despite phonological association of pitch accent and stressed syllable. Erroneous responses revealed a response bias towards the syllable with the f0 peak. In a visual-world eye-tracking study (Experiment 2), listeners fixated a stress competitor with initial stress more when the spoken target, which had penultimate stress, was realized with an early-peak accent (f0 peak preceding stressed syllable), compared to a condition with the f0 peak on the stressed syllable. Hence, high-pitched unstressed syllables are temporarily interpreted as stressed – a process directly affecting lexical activation. To investigate whether this stress competitor activation is guided by the frequent co-occurrence of high f0 and lexical stress, Experiment 3 increased the frequency of low-pitched stressed syllables in the immediate input. The effect of intonation on competitor fixations disappeared. Our findings are discussed with respect to a frequency-based mechanism and their implications for the nature of f0 processing.

Language change and linguistic inquiry in a world of multicompetence: Sustained phonetic drift and its implications for behavioral linguistic research Publication date: May 2019 Source: Journal of Phonetics, Volume 74 Author(s): Charles B. Chang Abstract Linguistic studies focusing on monolinguals have often examined individuals with considerable experience using another language. Results of a methodological review suggest that conflating ostensibly 'multicompetent' individuals with monolinguals is still common practice. A year-long longitudinal study of speech production demonstrates why this practice is problematic. Adult native English speakers recently arrived in Korea showed significant changes in their production of English stops and vowels (in terms of voice onset time, fundamental frequency, and formant frequencies) during Korean classes and continued to show altered English production a year later, months after their last Korean class. Consistent with an Incidental Processing Hypothesis (IPH) concerning the processing of ambient linguistic input, some changes persisted even in speakers who reported limited active use of Korean in their daily life. These patterns thus suggest that the linguistic experience obtained in a foreign language environment induces and then prolongs restructuring of the native language, making the multicompetent native speaker in a foreign language environment unrepresentative of a monolingual in a native language environment. Such restructuring supports the view that one's native language continues to evolve in adulthood, highlighting the need for researchers to be explicit about a population under study and to accordingly control (and describe) language background in a study sample.

Intonational structure mediates speech rate normalization in the perception of segmental categories Publication date: May 2019 Source: Journal of Phonetics, Volume 74 Author(s): Jeremy Steffman Abstract The question of if and to what extent listeners' perceptual phonetic categories are sensitive to prosodically driven variability has been a topic of interest in the literature. The present study reports on two experiments which address this question in light of recent research. In Experiment 1, listeners categorized a VOT continuum as /p/ or /b/ in a target syllable (/pɑ/ or /bɑ/). The target was placed in a carrier phrase where the duration and f0 of the pre-target syllable were manipulated. Results suggest listeners are sensitive to intonational structure in their computation of speech rate, interpreting a short syllable with low-rising f0 (created from an L-H% boundary tone in English intonational phonology) as an increase in speech rate. This perceived increase in rate shifts the category boundary of the subsequent target VOT. Experiment 2 showed listeners similarly adjusted categorization of a vowel duration continuum, where vowel duration is a cue to a following obstruent's voicing (categorized as "coat" or "code"). Taken together, these results suggest that listeners are sensitive to intonational structure in their perception of segmental contrasts and use the distribution of tonal targets over a given temporal interval in computing speech rate.

Acoustic correlates of word stress in Papuan Malay Publication date: May 2019 Source: Journal of Phonetics, Volume 74 Author(s): Constantijn Kaland Abstract The current study investigates acoustic correlates of word stress in Papuan Malay. This language is claimed to exhibit word stress, although empirical evidence is lacking. Moreover, related languages have been shown not to have stress, counter to earlier claims. Studies on stress in Austronesian languages have furthermore struggled to separate phrase level intonation phenomena from word level stress. The current study investigates a set of twelve potential acoustic correlates of stress, covering spectral, temporal and amplitudinal aspects of the speech signal. The measurements are taken from spontaneous Papuan Malay narratives. A subsequent comprehensive acoustic analysis was carried out and designed to avoid common pitfalls in the study of word stress. Results indicate that measures of duration, formant displacement and spectral tilt provide consistent evidence for the production of word stress in Papuan Malay.

Twenty-eight years of vowels: Tracking phonetic variation through young to middle age adulthood Publication date: May 2019 Source: Journal of Phonetics, Volume 74 Author(s): Susanne Gahl, R. Harald Baayen Abstract Research on age-related changes in speech has primarily focused on comparing "young" vs. "elderly" adults. Yet, listeners are able to guess talker age more accurately than a binary distinction would imply, suggesting that acoustic characteristics of speech change continually and gradually throughout adulthood. We describe acoustic properties of vowels produced by eleven talkers based on naturalistic speech samples spanning a period of 28 years, from ages 21 to 49. We find that the position of vowels in F1/F2 space shifts towards the periphery with increasing talker age. Based on Generalized Additive Mixed Effects models, we show that this shift is not fully attributable to changes in vowel duration or to segmental context. We discuss the implications of our results for research on aging and speech, and for research in which durational shortening and spectral characteristics of vowels are assumed to reflect a unitary process of phonetic reduction.

Alexandros Sfakianakis
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