Impact of Nonmodal Phonation on Estimates of Subglottal Pressure From Neck-Surface Acceleration in Healthy Speakers

Purpose The purpose of this study was to evaluate the effects of nonmodal phonation on estimates of subglottal pressure (Ps) derived from the magnitude of a neck-surface accelerometer (ACC) signal and to confirm previous findings regarding the impact of vowel contexts and pitch levels in a larger cohort of participants. Method Twenty-six vocally healthy participants (18 women, 8 men) were asked to produce a series of p-vowel syllables with descending loudness in 3 vowel contexts (/a/, /i/, and /u/), 3 pitch levels (comfortable, high, and low), and 4 elicited phonatory conditions (modal, breathy, strained, and rough). Estimates of Ps for each vowel segment were obtained by averaging the intraoral air pressure plateau before and after each segment. The root-mean-square magnitude of the neck-surface ACC signal was computed for each vowel segment. Three linear mixed-effects models were used to statistically assess the effects of vowel, pitch, and phonatory condition on the linear relationship (slope and intercept) between Ps and ACC signal magnitude. Results Results demonstrated statistically significant linear relationships between ACC signal magnitude and Ps within participants but with increased intercepts for the nonmodal phonatory conditions; slopes were affected to a lesser extent. Vowel and pitch contexts did not significantly affect the linear relationship between ACC signal magnitude and Ps. Conclusion The classic linear relationship between ACC signal magnitude and Ps is significantly affected when nonmodal phonation is produced by a speaker. Future work is warranted to further characterize nonmodal phonatory characteristics to improve the ACC-based prediction of Ps during naturalistic speech production.

On ejective fricatives in Omani Mehri

Ejective fricatives are extremely rare cross-linguistically. This infrequency is generally attributed to the incompatibility of two aerodynamic requirements: airflow to create noise frication and a high intraoral air pressure to implement ejectivity. Seeking to determine how this incompatibility is solved, this study presents an acoustic investigation of initial and intervocalic ejective fricatives in Mehri, a Modern South Arabian language spoken in Oman. Based on data from 5 Mehri speakers, the analysis of different temporal and non-temporal parameters shows a high degree of variability in the way ejectivity is implemented in fricatives. Much of this variability is shaped by the position of the segments within the word. In initial position, the ejectivity of fricatives translates into a frequent presence of post-frication glottal lags, higher intensity and higher center of gravity. These acoustic attributes are less frequently encountered in intervocalic position. In this position, it is argued, the systematic diphthongization of the following long vowel, induced by ejectivity combined with dorsopharyngealisation, is salient enough to allow the contrast of ejectivity to be recovered.

Affricating ejective fricatives: The case of Tigrinya

The production of an ejective fricative involves an aerodynamic dilemma. An ejective requires increased intraoral air pressure, while a fricative requires air to be continuously vented through a narrow constriction. This venting may defeat the pressure increase. Because ejectivity is realized by forming a complete oral closure, we hypothesize that complete closure (i.e. affrication) may also typify ejective fricatives in some languages. We test this hypothesis through an acoustic production experiment with speakers of Tigrinya. We find substantial evidence that Tigrinya /s’/ is commonly realized as [ts’] and comment on the plausibility of affrication as a general strategy for the realization of ejective fricatives.

Intraoral Air Pressure Discrimination under Conditions of Experimental Velopharyngeal Insufficiency

Objective This study assessed a single subject's ability to detect the difference limen (DLs) for his self-generated intraoral air pressure while his oral and nasal cavities were experimentally coupled. Method The subject, a 46-year-old man, uses a speech bulb prosthesis to cover an unrepaired cleft of his hard and soft palates. The subject's oral and nasal cavities were experimentally coupled by drilling different size holes through the speech-bulb component of the prosthesis to approximate conditions of velopharyngeal insufficiency. There were four hole-size conditions (10, 15, 20, and 30 mm2), a no-prosthesis condition, and pre- and postbaseline conditions with the prosthesis intact. The subject blew into a tube connected to a pressure transducer and was presented with a series of paired pressure loads. The first pressure load of each pair was the referent (1, 3, or 5 cm H2O), and the second was a preselected comparator load of a different amount. The subject blew into the tube with sufficient force to center the voltage meter's needle at the zero mark. The subject then reported whether the second pressure load required more, less, or equal breath pressure, compared with the referent pressure load of that pair. Results Size of the hole coupling the oral/nasal cavities did not significantly affect the subject's difference limen. Conclusion Experimental coupling of the oral/nasal cavities did not affect this subject's ability to detect differences in his self-generated intraoral air pressure.

Respiratory and Laryngeal Responses to an Oral Air Pressure Bleed During Speech

Researchers have hypothesized that the respiratory and laryngeal speech subsystems would respond to an air pressure bleed, but these responses have not been empirically studied. The present study examined the nature of the responses of the respiratory and laryngeal subsystems to an air pressure bleed in order to provide information relevant to the nature of motor control for speech. Participants produced a syllable train consisting of 7 syllables of [pα] 10 times with and without an air pressure bleed in place. Acoustic, aerodynamic, and respiratory kinematic data were collected. In the bleed condition, peak intraoral air pressure and average oral airflow during the [α] were lower, lung and rib cage volume excursions were longer, and rib cage volume terminations were more negative. This study provides empirical data demonstrating a clear interaction among the speech subsystems. Both active and passive mechanisms are suggested by the subsystems' responses.

Single Motor Unit Activity in Levator Veli Palatini during Speech and Nonspeech Tasks

Objective This article assesses the control of velar movement by relating observed recruitment patterns of single motor unit activity in levator veli palatini observed during speech and nonspeech tasks in a single subject to intraoral pressure demands. Methods Electromyographic activity was recorded from a single motor unit in levator veli palatini during repetitions of “Say ____ again” with selected consonant-vowel-consonant and consonant-vowel syllables, sustained high pressure consonants, and blowing tasks. Single motor unit firing characteristics (e.g., frequency of occurrence, firing frequency) were related to intraoral air pressures recorded during the sustained consonant and blowing tasks. Results Levator single motor unit activity was always present during the /s/ in “say” and the first and second /s/ in /sis/. Activity was observed less consistently during the production of the /s/ in /sus/, the /p/ in /p Λ/, and the /g/ in “again.” Single motor unit firing frequency ranged from 16.1 Hz to 22 Hz during phrase productions. Recruitment was observed during sustained productions of high-pressure consonants when intraoral pressures exceeded 15 cm H2O. Increases in intraoral air pressure were associated with 25% to 85% increases in single motor unit firing frequencies. During nonspeech blowing tasks, single motor unit activity was observed when intraoral air pressure exceeded approximately 12 cm H2O. Increases in intraoral air pressure were again associated with increased single motor unit firing rates. Conclusions Results showed evidence of both preprogrammed and feedback-controlled responses by levator veli palatini to changes in task intraoral pressure demands.

Temporal Characteristics of Velopharyngeal Function in Children

Objective This investigation was designed to examine the performance of children with normal speech on temporal aspects of aerodynamic tasks related to velopharyngeal closure. Design The investigation was a descriptive evaluation of variability in aerodynamic features related to velopharyngeal function during multiple repetitions of the word “hamper.” Setting Children without speech or velopharyngeal difficulties were seen in an experimental laboratory setting for the evaluation procedures. Participants Twenty-seven subjects were recruited for the experiment. Three subjects were rejected because of behavioral difficulties, and the remaining 24 subjects were subdivided into 4 groups of 6 children (3 males and 3 females) aged 3, 6, 9, and 12 years. The children, who were from local schools and day care centers, volunteered to participate in the experiment. All of the children had age-appropriate speech, language, and hearing abilities, as determined by screening tests administered by one of the examiners (L.T.). Main Outcome Measures Mean and variability of pressure-flow measures of peak intraoral air pressure and peak nasal airflow and the temporal measures accompanying each air pressure or airflow pulse were evaluated for the age groups of children examined in the experiment. Results The aerodynamic procedures employed to evaluate velopharyngeal closure during speech were reliable for use with young children. There was a numerical trend toward decreased duration of the temporal parameters with increasing age. Thus, children demonstrated durational values similar to those previously reported for normal-speaking adults. In general, peak oral air pressure and nasal airflow values were like those of previous investigations and demonstrated low variability across all age groups of children tested. Conclusions The data from the present investigation provide a preliminary base for comparison of temporal features of velopharyngeal closure for the aerodynamic evaluation of children with impaired velopharyngeal function.