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UBC Theses and Dissertations

Schlieren imaging : visualization of airflow in speech Rowell, Jeffrey


Schlieren imaging is a non-invasive research tool that enables real-time visualization of airflow through refraction of light. Used predominantly in aerospace and ballistics research, its suitability for observing airflow in speech was proposed nearly 40 years ago. To date, this potential has been virtually unexplored. The following proof-of-concept study investigates the visual correlates of nasal versus non-nasal airflow to provide a preliminary demonstration of the tool’s ability to visualize aerodynamic events in speech. Simultaneous schlieren and audio recordings were made of three French nasal/non-nasal minimal pairs spoken by eight native-French speakers. These stimuli were presented to 10 raters in Video-only, Audio-only and Combined Audio-Visual formats. The raters coded each stimulus as either “nasal” or “not nasal”. Accurate designation of Video-only stimuli was significantly above chance response (p < .05), indicating that the difference between airflow for nasal and non-nasal sounds can be visualized and perceived through schlieren imaging alone. Non-significant improvements were observed over time in the Video-only condition. Differences between Combined Audio-Visual and Audio-only stimuli were non-significant and likely influenced by a ceiling effect for the auditory information presented in both conditions. Further research is needed with more difficult auditory-perceptual tasks to explore potential supplementary advantages of schlieren visual feedback alongside auditory ratings of resonance. Future research may also benefit from improved training procedures for schlieren imaging. Nonetheless, schlieren imaging has promising potential for future implementation in both speech research and clinical applications, particularly for speech resonance disorders.

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