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Thread in response to the conversations I’ve been seeing about face masks and accessibility for deaf people.
There are good research-based reasons for not using clear masks. Some of this research has been led by deaf people. I’m going to post some articles.
There are good research-based reasons for not using clear masks. Some of this research has been led by deaf people. I’m going to post some articles.
But before I post the articles, I’ll say that deaf people generally know what we need. If someone does prefer clear masks, please use them. My own preference is a face shield by itself if I have to choose, but I would prefer a clear mask over a solid mask.
Clear masks have the benefit of leaving visual cues open that would be covered by sold masks. But they have the downside of blocking sound. This article describes some research on the topic. The first and second authors are CI users. https://www.audiology.org/audiology-today-julyaugust-2020/online-feature-more-speech-degradations-and-considerations-search?utm_source=BenchmarkEmail&utm_campaign=2020_0807_COVID_Week_in_Review&utm_medium=email
The major findings of this research: transparent masks block sound more than non-transparent masks and that adding a face shield on top of a mask can reduce the sound by up to 29 dB. Face shields have a major impact even when added to masks that more sound passes through.
For a hearing person, listening through a 29 dB sound blockage would be almost like losing the entire middle ear. Or listening with tightly fit earplugs. The middle ear provides a 30ish dB boost in sound.
Solid masks made of fabric reduce the sound by much less. Here’s an article describing some research on fabric face coverings and speech understanding. Thin fabrics block sound less than thick fabrics. Note: the participants in this study were hearing. https://theconversation.com/the-science-of-how-you-sound-when-you-talk-through-a-face-mask-139817
Traditional surgical masks also block sound to a lesser extent than transparent surgical masks and other transparent masks. The research described here had similar findings as described in the first article: 3-4 vs. 5 dB attenuation of sound. https://www.hearingreview.com/hearing-loss/health-wellness/how-do-medical-masks-degrade-speech-reception
Sound attenuation (i.e. how much is blocked) in summary:
- Transparent cloth mask: 21.2 dB
- Add a clear face shield to that: 29.2 dB
- Surgical mask: 3-5 dB
- Add a face shield: 20 dB
- Transparent surgical mask: 13.3 dB
- Add a face shield: 24.7 dB
- Transparent cloth mask: 21.2 dB
- Add a clear face shield to that: 29.2 dB
- Surgical mask: 3-5 dB
- Add a face shield: 20 dB
- Transparent surgical mask: 13.3 dB
- Add a face shield: 24.7 dB
Think about what this means for cochlear implant and hearing aid users. These devices don’t provide normal hearing. CI users generally have hearing levels around 25-30 dB HL. Let’s assume the best case scenario where the person hears at 20 dB HL across frequencies...
If someone uses a transparent cloth mask, add 21.2 dB to their hearing level. Transparent surgical mask, add 13.3 dB. Add a face shield on top of a transparent cloth mask and that person is now hearing very few speech sounds. Conversational speech is around 60-65 dBA.
Reading lips isn’t just visual. It’s impossible to get everything from a spoken signal just by reading the lips. The more sound access a person has, the better they can read lips. Different studies have reported that only ~30-50% of speech can be understood by reading lips.
So if sound is blocked, a deaf person who reads lips will have a much harder time doing it than usual. There’s a trade off: clear mask allows visual cues but blocks sound, and solid mask lets more sound through but blocks visual cues. There’s no perfect option.
Using a clear face shield alone is effective for some people. I haven’t seen any research on this, but from basic acoustics alone: sound bounces off things. It reverberates. Reverberation is stronger for hard, solid objects like face shields. Softer object absorb sound more.
If you’re speaking through a face shield, the air stream from your speech is hitting the shield and bouncing back at your face while also moving around the face shield. The person who is listening will lose some auditory information because of this.
This is why using a solid mask made of light material is better for *some* deaf people. Deaf people who use hearing tech have different preferences and needs. Some are more comfortable giving up visual cues for better auditory access and others would rather lose dB than visuals.
Two takeaways:
1) Always do what the individual deaf person prefers if there are options of clear masks, solid masks, and face shields.
2) Clear masks alone or plus face shields are not universally the best option for deaf people. This statement is supported by research.
1) Always do what the individual deaf person prefers if there are options of clear masks, solid masks, and face shields.
2) Clear masks alone or plus face shields are not universally the best option for deaf people. This statement is supported by research.
