Taehong Cho

Articulatory and acoustic studies on domain-initial strengthening in Korean

Abstract This study examines the effect of prosodic position on segmental properties of Korean consonants /n, t, t h , t * / along the articulatory parameters peak linguopalatal contact and stop seal duration, and several acoustic parameters. These parameters were compared in initial position in different domains of the Korean prosodic hierarchy. The first result is that consonants initial in higher prosodic domains are articulatorily stronger than those in lower domains, in the sense of having more linguopalatal contact. Second, there is a strong correlation between linguopalatal contact and duration (both articulatory and acoustic), suggesting that “strengthening” and “lengthening” is a single effect in Korean. We interpret this relation as one of undershoot: in weaker positions, consonants are shorter and undershoot contact targets. The different consonant manners of Korean can be characterized as varying in both duration and contact in this way. Third, there is another, less consistent, kind of lengthening and strengthening specific to Korean, namely that tense and aspirated consonant oral articulations can be longer and stronger word-medially than word-initially. Fourth, the acoustic properties VOT, total voiceless interval, %voicing during closure, nasal energy minimum, and to a lesser extent stop burst energy and voicing into closure, were found to vary with prosodic position and, in some cases, to correlate with linguopalatal contact. They could thus potentially provide cues to listeners about prosodic structure.

Prosodic strengthening and featural enhancement: Evidence from acoustic and articulatory realizations of /a,i/ in English

In this study the effects of accent and prosodic boundaries on the production of English vowels (/a,i/), by concurrently examining acoustic vowel formants and articulatory maxima of the tongue, jaw, and lips obtained with EMA (Electromagnetic Articulography) are investigated. The results demonstrate that prosodic strengthening (due to accent and/or prosodic boundaries) has differential effects depending on the source of prominence (in accented syllables versus at edges of prosodic domains; domain initially versus domain finally). The results are interpreted in terms of how the prosodic strengthening is related to phonetic realization of vowel features. For example, when accented, /i/ was fronter in both acoustic and articulatory vowel spaces (enhancing [-back]), accompanied by an increase in both lip and jaw openings (enhancing sonority). By contrast, at edges of prosodic domains (especially domain-finally), /i/ was not necessarily fronter, but higher (enhancing [+high]), accompanied by an increase only in the lip (not jaw) opening. This suggests that the two aspects of prosodic structure (accent versus boundary) are differentiated by distinct phonetic patterns. Further, it implies that prosodic strengthening, though manifested in fine-grained phonetic details, is not simply a low-level phonetic event but a complex linguistic phenomenon, closely linked to the enhancement of phonological features and positional strength that may license phonological contrasts.

Prosodically conditioned strengthening and vowel-to-vowel coarticulation in English

Abstract The goal of this study is to examine how the degree of vowel-to-vowel coarticulation varies as a function of prosodic factors such as nuclear-pitch accent (accented vs. unaccented), level of prosodic boundary (Prosodic Word vs. Intermediate Phrase vs. Intonational Phrase), and position-in-prosodic-domain (initial vs. final). It is hypothesized that vowels in prosodically stronger locations (e.g., in accented syllables and at a higher prosodic boundary) are not only coarticulated less with their neighboring vowels, but they also exert a stronger influence on their neighbors. Measurements of tongue position for English /a i/ over time were obtained with Carstens electromagnetic articulography. Results showed that vowels in prosodically stronger locations are coarticulated less with neighboring vowels, but do not exert a stronger influence on the articulation of neighboring vowels. An examination of the relationship between coarticulation and duration revealed that (a) accent-induced coarticulatory variation cannot be attributed to a duration factor and (b) some of the data with respect to boundary effects may be accounted for by the duration factor. This suggests that to the extent that prosodically conditioned coarticulatory variation is duration-independent, there is no absolute causal relationship from duration to coarticulation. It is proposed that prosodically conditioned V-to-V coarticulatory reduction is another type of strengthening that occurs in prosodically strong locations. The prosodically driven coarticulatory patterning is taken to be part of the phonetic signatures of the hierarchically nested structure of prosody.

Effects of initial position versus prominence in English

Abstract This study investigates effects of three prosodic factors—prosodic boundary (Utterance-initial vs. Utterance-medial), lexical stress (primary vs. secondary) and phrasal accent (accented vs. unaccented)—on articulatory and acoustic realizations of word-initial CVs (/ne/, /te/) in trisyllabic English words. The consonantal measures were linguopalatal Peak contact and Release contacts (by electropalatography), Seal duration, Nasal duration and Nasal energy for /n/, VOT, RMS burst energy and spectral Center of Gravity at the release for /t/; and the vocalic measures were linguopalatal Vowel contact, Vowel F1, Vowel duration and Vowel amplitude. Several specific points emerge. Firstly, domain-initial articulation is differentiated from stress- or accent-induced articulations along several measures. Secondly, the vowel is effectively louder domain-initially, suggesting that the boundary effect is not strictly local to the initial consonant. Thirdly, some accentual effects can be seen in secondary-stressed syllables, suggesting that accentual influences spread beyond the primary-stressed syllable. Finally, unlike domain-initial effects, prominence effects are not cumulative. Thus we conclude that, at least for the kind of word-initial syllables tested here, different aspects of prosodic structure (domain boundary vs. prominence) are differentially encoded.

Prosodic influences on consonant production in Dutch: Effects of prosodic boundaries, phrasal accent and lexical stress

Prosodic influences on phonetic realizations of four Dutch consonants (/t d s z/) were examined. Sentences were constructed containing these consonants in word-initial position; the factors lexical stress, phrasal accent and prosodic boundary were manipulated between sentences. Eleven Dutch speakers read these sentences aloud. The patterns found in acoustic measurements of these utterances (e.g.,voice onset time (VOT),consonant duration,voicing during closure,spectral center of gravity,burst energy) indicate that the low-level phonetic implementation of all four consonants is modulated by prosodic structure. Boundary effects on domain-initial segments were observed in stressed and unstressed syllables,extending previous findings which have been on stressed syllables alone. Three aspects of the data are highlighted. First,shorter VOTs were found for /t/ in prosodically stronger locations (stressed,accented and domaininitial),as opposed to longer VOTs in these positions in English. This suggests that prosodically driven phonetic realization is bounded by language-specific constraints on how phonetic features are specified with phonetic content: Shortened VOT in Dutch reflects enhancement of the phonetic feature {� spread glottis}, while lengthened VOT in English reflects enhancement of {+spread glottis}. Prosodic strengthening therefore appears to operate primarily at the phonetic level,such that prosodically driven enhancement of phonological contrast is determined by phonetic implementation of these (language-specific) phonetic features. Second,an accent effect was observed in stressed and unstressed syllables,and was independent of prosodic boundary size. The domain of accentuation in Dutch is thus larger than the foot. Third,within a

Prosodically driven phonetic detail in speech processing: The case of domain-initial strengthening in English

Abstract We explore the role of the acoustic consequences of domain-initial strengthening in spoken-word recognition. In two cross-modal identity-priming experiments, listeners heard sentences and made lexical decisions to visual targets, presented at the onset of the second word in two-word sequences containing lexical ambiguities (e.g., bus tickets, with the competitor bust). These sequences contained Intonational Phrase (IP) or Prosodic Word (Wd) boundaries, and the second words initial Consonant and Vowel (CV, e.g., [tɪ]) was spliced from another token of the sequence in IP- or Wd-initial position. Acoustic analyses showed that IP-initial consonants were articulated more strongly than Wd-initial consonants. In Experiment 1, related targets were post-boundary words (e.g., tickets). No strengthening effect was observed (i.e., identity priming effects did not vary across splicing conditions). In Experiment 2, related targets were pre-boundary words (e.g., bus). There was a strengthening effect (stronger priming when the post-boundary CVs were spliced from IP-initial than from Wd-initial position), but only in Wd-boundary contexts. These were the conditions where phonetic detail associated with domain-initial strengthening could assist listeners most in lexical disambiguation. We discuss how speakers may strengthen domain-initial segments during production and how listeners may use the resulting acoustic correlates of prosodic strengthening during word recognition.

Optical Phonetics and Visual Perception of Lexical and Phrasal Stress in English

In a study of optical cues to the visual perception of stress, three American English talkers spoke words that differed in lexical stress and sentences that differed in phrasal stress, while video and movements of the face were recorded. The production of stressed and unstressed syllables from these utterances was analyzed along many measures of facial movement, which were generally larger and faster in the stressed condition. In a visual perception experiment, 16 perceivers identified the location of stress in forced-choice judgments of video clips of these utterances (without audio). Phrasal stress was better perceived than lexical stress. The relation of the visual intelligibility of the prosody of these utterances to the optical characteristics of their production was analyzed to determine which cues are associated with successful visual perception. While most optical measures were correlated with perception performance, chin measures, especially Chin Opening Displacement, contributed the most to correct perception independently of the other measures. Thus, our results indicate that the information for visual stress perception is mainly associated with mouth opening movements.

Effects of Morpheme Boundaries on Intergestural Timing: Evidence from Korean

This paper examines the effects of morpheme boundaries on intergestural timing, and demonstrates that low-level phonetic realization is influenced by morphological structure, i.e. compounding and affixation. It reports two experiments, one using electromagnetic midsagittal articulography (EMA) and one electropalatography (EPG), examining Korean data. The results of the EMA study show that intergestural timing is less variable for adjacent gestures across the word boundary inside a lexicalized compound than inside a nonlexicalized compound, and inside a monomorphemic word than across a morpheme boundary. The EPG study (which examined the timing in palatalization of a coronal) shows that both [ti] and [ni] have more variability in gestural timing when heteromorphemic than when tautomorphemic. Furthermore, the phonetic details of gestural overlap shed light on the asymmetry on palatalization between tautomorphemic and heteromorphemic gestural sequences (e.g. ni vs. n-i), presumably driven by paradigmatic contrast and preference of overlap. In short, what emerges from two experiments is that gestures are coordinated more stably within a single lexical item (a morpheme or a lexicalized compound) than across a boundary between lexical items. In accounting for the stability of intergestural timing within a lexical entry, several hypotheses were discussed including the Phase Window, Bonding Strength, Phonological Timing and Extended Phase Window model newly proposed here. The implication is that the morphological structure may be encoded in the phonetic realization, as is the case with other linguistic structure (e.g. prosodic structure).

Communicatively driven versus prosodically driven hyper-articulation in Korean

Abstract This study investigated how three different kinds of hyper-articulation, one communicatively driven (in clear speech), and two prosodically driven (with boundary and prominence/focus), are acoustic-phonetically realized in Korean. Several important points emerged from the results obtained from an acoustic study with eight speakers of Seoul Korean. First, clear speech gave rise to global modification of the temporal and prosodic structures over the course of the utterance, showing slowing down of the utterance and more prosodic phrases. Second, although the three kinds of hyper-articulation were similar in some aspects, they also differed in many aspects, suggesting that different sources of hyper-articulation are encoded separately in speech production. Third, the three kinds of hyper-articulation interacted with each other; the communicatively driven hyper-articulation was prosodically modulated, such that in a clear speech mode not every segment was hyper-articulated to the same degree, but prosodically important landmarks (e.g., in IP-initial and/or focused conditions) were weighted more. Finally, Korean, a language without lexical stress and pitch accent, showed different hyper-articulation patterns compared to other, Indo-European languages such as English—i.e., it showed more robust domain-initial strengthening effects (extended beyond the first initial segment), focus effects (extended to V1 and V2 of the entire bisyllabic test word) and no use of global F0 features in clear speech. Overall, the present study suggests that the communicatively driven and the prosodically driven hyper-articulations are intricately intertwined in ways that reflect not only interactions of principles of gestural economy and contrast enhancement, but also language-specific prosodic systems, which further modulate how the three kinds of hyper-articulations are phonetically expressed.

Prosodic strengthening of German fricatives in duration and assimilatory devoicing

Abstract This study addressed prosodic effects on the duration of and amount of glottal vibration in German word-initial fricatives /f, v, z/ in assimilatory and non-assimilatory devoicing contexts. Fricatives following /ə/ (non-assimilation context) were longer and were produced with less glottal vibration after higher prosodic boundaries, reflecting domain-initial prosodic strengthening. After /t/ (assimilation context), lenis fricatives (/v, z/) were produced with less glottal vibration than after /ə/, due to assimilatory devoicing. This devoicing was especially strong across lower prosodic boundaries, showing the influence of prosodic structure on sandhi processes. Reduction in glottal vibration made lenis fricatives more fortis-like (/f, s/). Importantly, fricative duration, another major cue to the fortis-lenis distinction, was affected by initial lengthening, but not by assimilation. Hence, at smaller boundaries, fricatives were more devoiced (more fortis-like), but also shorter (more lenis-like). As a consequence, the fortis and lenis fricatives remained acoustically distinct in all prosodic and segmental contexts. Overall, /z/ was devoiced to a greater extent than /v/. Since /z/ does not have a fortis counterpart in word-initial position, these findings suggest that phonotactic restrictions constrain phonetic processes. The present study illuminates a complex interaction of prosody, sandhi processes, and phonotactics, yielding systematic phonetic cues to prosodic structure and phonological distinctions.