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.