The stop-like modification of /ð/ : a case study in the analysis and handling of speech variation

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2007.Includes bibliographical references (leaves 138-142).Phonetic variation is pervasive in everyday speech. Studying these variations is essential for building acoustic models and lexical representations that effectively capture the variability of speech. This thesis examines one of the commonly-occurring phonetic variations in English: the stop-like modification of the dental fricative /ð/. This variant exhibits a drastic change from the canonical /ð/; the manner of production is changed from one that is fricative to one that is stop-like. Furthermore, the place of articulation of stop-like /0/ has been a point of uncertainty, leading to the confusion between stop-like /ð/1 and /d/. This thesis aims to uncover the segmental context of stop-like /ð/, possible causes of the modification, whether the dental place of articulation is preserved despite modification, and if there are salient acoustic cues that distinguish between stop-like /ð/ and /d/. Word-initial /ð/ in the read speech of the TIMIT Database, the task-oriented spontaneous speech of the AEMT Corpus, and the non-task-oriented spontaneous speech of the Buckeye Corpus are examined acoustically. It is found that stop-like /ð/ occurs most often when it is preceded by silence or when preceded by a stop consonant. The occurrence is less frequent when /ð/ is preceded by a fricative or an affricate consonant. This modification rarely occurs when /ð/ is preceded by a vowel or liquid consonant. The findings suggest that possible factors that may contribute to the stop-like modification of /ð/include physiological mechanisms of speech production, prosody, and/or other aspects of speaking style and manner. Acoustic analysis indicates that stop-like /ð/ is significantly different from /d/ in burst amplitude, burst spectrum shape, burst peak frequency, and second formant at following- vowel onset.(cont.) Moreover, the acoustic differences indicate that the dental place of articulation is preserved for stop-like /ð/. Automatic classification experiments involving these acoustic measures suggest that they are robust in distinguishing stop-like /ð/ from /d/. Applications of these findings may lie in areas of automatic speech recognition, speech transcription, and development of acoustic measures for speech disorder diagnosis.by Sherry Y. Zhao.Ph.D

How do voiced retroflex stops evolve? Evidence from typology and an articulatory study

The present article illustrates that the specific articulatory and aerodynamic requirements for voiced but not voiceless alveolar or dental stops can cause tongue tip retraction and tongue mid lowering and thus retroflexion of front coronals. This retroflexion is shown to have occurred diachronically in the three typologically unrelated languages Dhao (Malayo-Polynesian), Thulung (Sino-Tibetan), and Afar (East-Cushitic). In addition to the diachronic cases, we provide synchronic data for retroflexion from an articulatory study with four speakers of German, a language usually described as having alveolar stops. With these combined data we supply evidence that voiced retroflex stops (as the only retroflex segments in a language) did not necessarily emerge from implosives, as argued by Haudricourt (1950), Greenberg (1970), Bhat (1973), and Ohala (1983). Instead, we propose that the voiced front coronal plosive /d/ is generally articulated in a way that favours retroflexion, that is, with a smaller and more retracted place of articulation and a lower tongue and jaw position than /t/

Phonetic variability and grammatical knowledge: an articulatory study of Korean place assimilation.

The study reported here uses articulatory data to investigate Korean place assimilation of coronal stops followed by labial or velar stops, both within words and across words. The results show that this place-assimilation process is highly variable, both within and across speakers, and is also sensitive to factors such as the place of articulation of the following consonant, the presence of a word boundary and, to some extent, speech rate. Gestures affected by the process are generally reduced categorically (deleted), while sporadic gradient reduction of gestures is also observed. We further compare the results for coronals to our previous findings on the assimilation of labials, discussing implications of the results for grammatical models of phonological/phonetic competence. The results suggest that speakers’ language-particular knowledge of place assimilation has to be relatively detailed and context-sensitive, and has to encode systematic regularities about its obligatory/variable application as well as categorical/gradient realisation

Effects of Palatal Expansion on Speech Production

Introduction: Rapid palatal expanders (RPEs) are a commonly used orthodontic adjunct for the treatment of posterior crossbites. RPEs are cemented to bilateral posterior teeth across the palate and thus may interfere with proper tongue movement and linguopalatal contact. The purpose of this study was to identify what specific role RPEs have on speech sound production for the child and early adolescent orthodontic patient. Materials and Methods: RPEs were treatment planned for patients seeking orthodontics at Marquette University. Speech recordings were made using a phonetically balanced reading passage (“The Caterpillar”) at 3 time points: 1) before RPE placement; 2) immediately after cementation; and 3) 10-14 days post appliance delivery. Measures of vocal tract resonance (formant center frequencies) were obtained for vowels and measures of noise distribution (spectral moments) were obtained for consonants. Two-way repeated measures (ANOVA) was used along with post-hoc tests for statistical analysis. Results: For the vowel /i/, the first formant increased and the second formant decreased indicating a more inferior and posterior tongue position. For /e/, only the second formant decreased resulting in a more posterior tongue position. The formants did not return to baseline within the two-week study period. For the fricatives /s/, //, /t/, and /k/, a significant shift from high to low frequencies indicated distortion upon appliance placement. Of these, only /t/ fully returned to baseline during the study period. Conclusion: Numerous phonemes were distorted upon RPE placement which indicated altered speech sound production. For most phonemes, it takes longer than two weeks for speech to return to baseline, if at all. Clinically, the results of this study will help with pre-treatment and interdisciplinary counseling for orthodontic patients receiving palatal expanders

Changes in the McGurk Effect Across Phonetic Contexts

To investigate the process underlying audiovisual speech perception, the McGurk illusion was examined across a range of phonetic contexts. Two major changes were found. First, the frequency of illusory /g/ fusion percepts increased relative to the frequency of illusory /d/ fusion percepts as vowel context was shifted from /i/ to /a/ to /u/. This trend could not be explained by biases present in perception of the unimodal visual stimuli. However, the change found in the McGurk fusion effect across vowel environments did correspond systematically with changes in second format frequency patterns across contexts. Second, the order of consonants in illusory combination percepts was found to depend on syllable type. This may be due to differences occuring across syllable contexts in the timecourses of inputs from the two modalities as delaying the auditory track of a vowel-consonant stimulus resulted in a change in the order of consonants perceived. Taken together, these results suggest that the speech perception system either fuses audiovisual inputs into a visually compatible percept with a similar second formant pattern to that of the acoustic stimulus or interleaves the information from different modalities, at a phonemic or subphonemic level, based on their relative arrival times.National Institutes of Health (R01 DC02852

Spoken word classification in children and adults

Purpose: Preschool children often have difficulties in word classification, despite good speech perception and production. Some researchers suggest they represent words using phonetic features rather than phonemes. We examine whether there is a progression from feature based to phoneme based processing across age groups, and whether responses are consistent across tasks and stimuli. Method: In Study 1, 120 3 to 5 year old children completed three tasks assessing use of phonetic features in classification, with an additional 58 older children completing one of the three tasks. In Study 2, all of the children, together with an additional adult sample, completed a nonword learning task. Results: In all four tasks, children classified words sharing phonemes as similar. In addition, children regarded words as similar if they shared manner of articulation, particularly word-finally. Adults also showed this sensitivity to manner, but across the tasks there was a pattern of increasing use of phonemic information with age. Conclusions: Children tend to classify words as similar if they share phonemes or share manner of articulation word finally. Use of phonemic information becomes more common with age. These findings are in line with the theory that phonological representations become more detailed in the preschool years

Ejectives in Scottish English: a social perspective

This paper presents the results of an analysis of the realization of word-final /k/ in a sample of read and casual speech by 28 female pupils from a single-sex Glaswegian high school. Girls differed in age, socioeconomic background, and ethnicity. Ejectives were the most usual variant for /k/ in both speech styles, occurring in the speech of every pupil in our sample. Our narrow auditory analysis revealed a continuum of ejective production, from weak to intense stops. Results from multinomial logistic regression show that ejective production is promoted by phonetic, linguistic and interactional factors: ejectives were used more in read speech, when /k/ occurred in the /-ŋk/ cluster (e.g. tank), and when the relevant word was either at the end of a clause or sentence, or in turn-final position. At the same time, significant interactions between style, and position in turn, and the social factors of age and ethnicity, show that the use of ejectives by these girls is subject to a fine degree of sociolinguistic control, alongside interactional factors. Finally, cautious comparison of these data with recordings made in 1997 suggests that these results may also reflect a sound change in progress, given the very substantial real-time increase in ejective realizations of /k/ in Glasgow over the past fourteen years

Changes in the McGurk Effect across Phonetic Contexts. I. Fusions

The McGurk effect has generally been studied within a limited range of phonetic contexts. With the goal of characterizing the McGurk effect through a wider range of contexts, a parametric investigation across three different vowel contexts, /i/, /α/, and /u/, and two different syllable types, consonant-vowel (CV) and vowel-consonant (VC), was conducted. This paper discusses context-dependent changes found specifically in the McGurk fusion phenomenon (Part II addresses changes found in combination percepts). After normalizing for differences in the magnitude of the McGurk effect in different contexts, a large qualitative change in the effect across vowel contexts became apparent. In particular, the frequency of illusory /g/ percepts increased relative to the frequency of illusory /d/ percepts as vowel context was shifted from /i/ to /α/ to /u/. This trend was seen in both syllable sets, and held regardless of whether the visual stimulus used was a /g/ or /d/ articulation. This qualitative change in the McGurk fusion effect across vowel environments corresponded systematically with changes in the typical second formant frequency patterns of the syllables presented. The findings are therefore consistent with sensory-based theories of speech perception which emphasize the importance of second formant patterns as cues in multimodal speech perception.National Institue on Deafness and other Communication Disorders (R29 02852); Alfred P. Sloan Foundation and National Institute on Deafness and other Communication Disorders (R29 02852

Developmental trends in voice onset time: some evidence for sex differences

This study reports on an investigation into the voice onset time (VOT) patterns of the plosives /p b t d/ in a group of 30 children aged 7 (n = 10), 9 (n = 10) and 11 (n = 10) years. Equal numbers of girls and boys participated in the study. Each child named a series of letter objects to elicit /p b t d/ in a syllable onset position with a fixed vowel context. VOT data were examined for age, sex and plosive differences with the following hypotheses: Firstly, that there would be sex differences in the VOT patterns of preadolescent children. Secondly, that the sex differences in VOT patterns would be linked to age and development, and that these would eventually become marked by the age of 11 years, by which time adult-like VOT values should have been achieved. Finally, that the extent of sex and age differences would be dependent upon the plosive being investigated. Results indicated patterns of decrease with age in the VOT values of /p b/ for the boys, with some evidence of increases in the VOT values of /t/ for the girls. In addition, 'voiced' and 'voiceless' cognates showed a more marked bimodal distribution in the girls' VOT patterns. This bimodal distribution was investigated by examining the degree of difference between the VOT values of voiced and voiceless cognate pairs /p b/ and /t d/, and examining the effects of age, sex and cognate pair. These results indicated that more marked sex differences in the 'voiced'/'voiceless' contrast emerged between the data of the 9- and 11-year-olds, a pattern, which was more marked for the alveolar plosives. These preliminary results confirmed all three hypotheses. The findings are presented and discussed both within a developmental and sociophonetic framework

Developmental trends in voice onset time: some evidence for sex differences

This study reports on an investigation into the voice onset time (VOT) patterns of the plosives /p b t d/ in a group of 30 children aged 7 (n = 10), 9 (n = 10) and 11 (n = 10) years. Equal numbers of girls and boys participated in the study. Each child named a series of letter objects to elicit /p b t d/ in a syllable onset position with a fixed vowel context. VOT data were examined for age, sex and plosive differences with the following hypotheses: Firstly, that there would be sex differences in the VOT patterns of preadolescent children. Secondly, that the sex differences in VOT patterns would be linked to age and development, and that these would eventually become marked by the age of 11 years, by which time adult-like VOT values should have been achieved. Finally, that the extent of sex and age differences would be dependent upon the plosive being investigated. Results indicated patterns of decrease with age in the VOT values of /p b/ for the boys, with some evidence of increases in the VOT values of /t/ for the girls. In addition, 'voiced' and 'voiceless' cognates showed a more marked bimodal distribution in the girls' VOT patterns. This bimodal distribution was investigated by examining the degree of difference between the VOT values of voiced and voiceless cognate pairs /p b/ and /t d/, and examining the effects of age, sex and cognate pair. These results indicated that more marked sex differences in the 'voiced'/'voiceless' contrast emerged between the data of the 9- and 11-year-olds, a pattern, which was more marked for the alveolar plosives. These preliminary results confirmed all three hypotheses. The findings are presented and discussed both within a developmental and sociophonetic framework