Category Archives: Applied

These posts are dedicated to individual and joint applied research projects. That is, research that has an immediate socially useful outcome

Exploring how speech air flow may impact the spread of airborne diseases

I am participating on an American Association for the Advancement of Science (AAAS) 2022 meeting panel on “Transmission of Airborne Pathogens through Expiratory Activities” on Friday, February 18th from 6:00 to 6:45 AM Greenwich mean time. You can register for the meeting by clicking here. In advance of that meeting, the University of British Columbia asked me some Q&A questions exploring how speech air flow may impact the spread of airborne diseases.

The AAAS meeting itself is hosted by Prof. Bryan Gick of the University of British Columbia. It has individual talks by Dr. Sima Asadi on “Respiratory behavior and aerosol particles in airborne pathogen transmission”, Dr. Nicole M. Bouvier on “Talking about respiratory infectious disease transmission”, and myself on “Human airflow while breathing, speaking, and singing with and without masks”.

Dr. Sima Asadi’s talk focuses on the particles emitted during human speech, and the efficacy of masks in controlling their outward emission. For this work, Sima received the Zuhair A. Munir Award for the Best Doctoral Dissertation in Engineering from UC Davis in 2021. She is currently a postdoctoral associate in Chemical Engineering at MIT (Boston).

Dr. (Prof) Nicole M. Bouvier is an associate professor of Medicine and Infectious Diseases and Microbiology at the Icahn School of Medicine at Mount Sinai (New York). Nichole discusses how we understand the roots by which respiratory microorganisms, like viruses and bacteria, transmit between humans, which is fundamental in how we develop both medical and public health countermeasures to reduce or prevent their spread. However, much of what we think we know is based on evidence that is incomplete at best, and full of confusing terminology, as the current COVID-19 pandemic has made abundantly clear.

I myself am new to airborne transmission research, coming instead from the perspective that visual and aero-tactile speech help with speech perception, and so masks would naturally interfere with clear communication. They would do this by potentially muffling some speech sounds, but mostly by cutting off the perceiver form visual and even tactile speech signals.

However, since my natural interests involve speech air flow, I was ideally suited to move into research studying how these same air flows may be reduced or eliminated by face masks. I conduct this research with a Mechanical Engineering team at the University of Canterbury, and some of their results are featured in my individual presentation. Our most recent publication on Speech air flow with and without face masks was highlighted in previous posts on Maps of Speech, and in a YouTube video found here.

Speech air flow with and without face masks

It took a while due to the absolutely shocking amount of work required for the “Gait change in tongue movement” article, but Natalia Kabaliuk, Luke Longworth, Peiman Pishyar‑Dehkordi, Mark Jermy and I were able to get our article on “Speech air flow with and without face masks” accepted to Scientific Reports (Nature Publishing Group). The article is now out (though a pre-review version had been available since we submitted this article to Sci Rep). You can also watch my YouTube video describing many of the results.

Here is an example of a low-stiffness air-flow from a porous mask, which allows leaks from the tops, bottoms, and sides, and forward flow prevention, as taken from Figure 5 of the article.

Figure 5. Audio and Schlieren of speech through a porous face mask (Frame 621, 1st block, CORI Supermask). Image from 88 ms after the release burst for the [kh ] in “loch”. Note that the k’s puff is smoother and less well defined than the one in Fig. 2, but still has eddies that change air-density across the span of the puff. The red-dashed line in the audio waveform indicates the timing of the schlieren frame.

And here is an example of typical higher-stiffness flow from a less porous mask from Figure 8.

Figure 8. Audio and Schlieren of speech with a tightly fitting surgical mask (Frame 334, 1st block, Henry Schlein surgical mask [level 2]). Air slowly flows out above the eyes, floating out and upward continuously. The red-dashed line in the audio waveform indicates the timing of the schlieren frame.

Masks can be made to fit tighter, as in well-designed KN95/N95 masks and masks with metal strips at the nose to prevent upward-escaping air flow. However, for all the masks we studied, the tradeoff was not entirely avoided. And with that, here is our abstract:

Face masks slow exhaled air flow and sequester exhaled particles. There are many types of face masks on the market today, each having widely varying fits, filtering, and air redirection characteristics. While particle filtration and flow resistance from masks has been well studied, their effects on speech air flow has not. We built a schlieren system and recorded speech air flow with 14 different face masks, comparing it to mask-less speech. All of the face masks reduced air flow from speech, but some allowed air flow features to reach further than 40 cm from a speaker’s lips and nose within a few seconds, and all the face masks allowed some air to escape above the nose. Evidence from available literature shows that distancing and ventilation in higher-risk indoor environment provide more benefit than wearing a face mask. Our own research shows all the masks we tested provide some additional benefit of restricting air flow from a speaker. However, well-fitted mask specifically designed for the purpose of preventing the spread of disease reduce air flow the most. Future research will study the effects of face masks on speech communication in order to facilitate cost/benefit
analysis of mask usage in various environments.

Ultrasound Transducer Stabilizer for Children.

Our three-dimensional printable ultrasound transducer stabilizer has been a huge success. It is in use here at the University of Canterbury, as well as the University of Michigan, Hiroshima University, University of California, Los Angeles, and soon at the University of British Columbia. (And it is available at Western Sydney University).

However, Phil Hoole at Ludwig Maximilian University of Munich figured out that the transducer stabilizer does *not* work with Children. He developed a solution to that problem, and I am making it available here. Within this zip file, there is a new probe holder. The base and clip-holder should be printed as is. Each remaining file needs to be scaled to 75% of their size and then printed. Each file marked with X2 needs to be printed *twice*.

I will put photos of this version of the probe-holder online once I have printed new copies and sewn all the pieces together sometime in October.

Rivener – a maskless airflow estimation and nasalance system

Myself, Jenna Duerr, and Rachel Grace Kerr recently published an article documenting the main instrumental uses for Rivener, our mask-less air flow estimation and nasalance system. This device records audio and low-frequency pseudo-sound with microphones placed at the nose and mouth, separated by a baffle and placed in a Venturi tube to prevent that pseudo-sound from overloading the circuitry.  The device can record all the aspects of hearing-impaired speech without interfering with the audio quality of the speaker or requiring physical contact with the system.  If you want a detailed description of what the system can do, here is an unpublished “white paper” documenting the strengths and limitations of the system in detail.

3D-printable ultrasound probe stabilizer for speech research

Christopher Carignan, Wei-rong Chen, Muawiyath ShujauCatherine T. Best, and I recently published an article about our new 3D-printable ultrasound transducer stabilizer (probe holder). 

Ultrasound tongue imaging of speech requires the imaging probe to remain stable throughout data collection. Previous solutions to this stabilization problem have often been too cumbersome and/or expensive for wide-spread use. Our solution improves upon previous designs in both functionality and comfort, while also representing the first free and open-source 3D printable headset for both academic and clinical applications of ultrasound tongue imaging.

The non-metallic design permits the simultaneous collection of ultrasound and electromagnetic articulometry. For clinicians, the headset eliminates the need for holding the imaging probe manually, allowing them to interact with patients in an unencumbered way.

The printable materials we provided work for midsaggital imaging of the tongue using a few select ultrasound transducers like the Logiq E 8C-RS and the Telemed transducers for Articulate Instruments systems, but can be modified easily to allow for other probes, or for coronal tongue imaging.

The system costs from $200 (for a 100 micron print) to $600 USD (for a 20 micron print) in materials to produce, making it quite affordable.  It is also very comfortable compared to most stabilization systems, and is accurate to within about 2mm of motion in any direction, and 2 degrees of rotation in any direction.  More details can be found in the article documenting the system.

Here is an image of the system, fully assembled and worn:

Transducer stabilizer

Transducer stabilizer