Schlieren Study of External Airflow during the Production of Nasal and Oral Vowels in French

Schlieren imaging enables real-time visualization of airflow through refraction of light. The potential of schlieren imaging for speech research was first proposed nearly 40 years ago [1]. A recent study tested this proposal [2]. Phonetically trained raters coded schlieren recordings of French vowels as oral versus nasal [2] (Figure 1). Although raters discriminated between the oral and nasal vowels (p < .05), the study could not fully determine whether the perceptual ratings were based on airflow patterns alone. Thus, the current study was undertaken to investigate optical flow analysis in detecting differences between oral and nasal airflow patterns in the same schlieren recordings. Results show that nasal vowels are produced with a larger magnitude of nasal airflow than oral vowels, with some variation between speakers.