A model of speech production based on the acoustic relativity of the vocal tract

The relation of velopharyngeal coupling area and vocal tract scaling to identification of stop-nasal cognates

The purpose of this study was to determine whether the threshold of velopharyngeal (VP) coupling area at which listeners switch from identifying a consonant as a stop to a nasal in North American English was different for speech produced by a model based on an adult male, an adult female, and a 4-year-old child. V1CV2 stimuli were generated with a speech production model that encodes phonetic segments as relative acoustic targets imposed on an underlying vocal tract and laryngeal structure that can be scaled according to sex and age. Each V1CV2 was synthesized with a set of VP coupling functions whose maximum area ranged from 0 to 0.1 cm2. Results showed that scaling the vocal tract and vocal folds had essentially no effect on the VP coupling area at which listener identification shifted from stop to nasal. The range of coupling areas at which the crossover occurred was 0.037-0.049 cm2 for the male model, 0.040-0.055 cm2 for the female model, and 0.039-0.052 cm2 for the 4-year-old child model, and overall mean was 0.044 cm2. Calculations of band limited peak nasalance indicated that 85% peak nasalance during the consonant was well aligned with listener responses.

Anatomic development of the upper airway during the first five years of life: A three-dimensional imaging study

Purpose

Normative data on the growth and development of the upper airway across the sexes is needed for the diagnosis and treatment of congenital and acquired respiratory anomalies and to gain insight on developmental changes in speech acoustics and disorders with craniofacial anomalies.

Methods

The growth of the upper airway in children ages birth to 5 years, as compared to adults, was quantified using an imaging database with computed tomography studies from typically developing individuals. Methodological criteria for scan inclusion and airway measurements included: head position, histogram-based airway segmentation, anatomic landmark placement, and development of a semi-automatic centerline for data extraction. A comprehensive set of 2D and 3D supra- and sub-glottal measurements from the choanae to tracheal opening were obtained including: naso-oro-laryngo-pharynx subregion volume and length, each subregion’s superior and inferior cross-sectional-area, and antero-posterior and transverse/width distances.

Results

Growth of the upper airway during the first 5 years of life was more pronounced in the vertical and transverse/lateral dimensions than in the antero-posterior dimension. By age 5 years, females have larger pharyngeal measurement than males. Prepubertal sex-differences were identified in the subglottal region.

Conclusions

Our findings demonstrate the importance of studying the growth of the upper airway in 3D. As the lumen length increases, its shape changes, becoming increasingly elliptical during the first 5 years of life. This study also emphasizes the importance of methodological considerations for both image acquisition and data extraction, as well as the use of consistent anatomic structures in defining pharyngeal regions.

The relation of velopharyngeal coupling area to the identification of stop versus nasal consonants in North American English based on speech generated by acoustically driven vocal tract modulations

The purpose of this study was to determine the threshold of velopharyngeal coupling area at which listeners switch from identifying a consonant as a stop to a nasal in North American English, based on V₁CV₂ stimuli generated with a speech production model that encodes phonetic segments as relative acoustic targets. Each V₁CV₂ was synthesized with a set of velopharyngeal coupling functions whose area ranged from 0 to 0.1 cm². Results show that consonants were identified by listeners as a stop when the coupling area was less than 0.035-0.057 cm², depending on place of articulation and final vowel. The smallest coupling area (0.035 cm²) at which the stop-to-nasal switch occurred was found for an alveolar consonant in the /ɑCi/ context, whereas the largest (0.057 cm²) was for a bilabial in /ɑCɑ/. For each stimulus, the balance of oral versus nasal acoustic energy was characterized by the peak nasalance during the consonant. Stimuli with peak nasalance below 40% were mostly identified by listeners as stops, whereas those above 40% were identified as nasals. This study was intended to be a precursor to further investigations using the same model but scaled to represent the developing speech production system of male and female talkers.

Identification of voiced stop consonants produced by acoustically driven vocal tract modulations

A recently developed speech production model, in which speech segments are specified by relative acoustic events called resonance deflection patterns, was used to generate speech signals that were presented to listeners in a perceptual test. The purpose was to determine the effect of variations of the magnitude and polarity of the third resonance deflection on identification of the consonant in a V₁CV₂ disyllable while the deflections of the first and second resonances were held constant. Result showed that listeners' identification changed from /d/ to /ɡ/ when the polarity of the third resonance deflection switched from positive to negative.