Impact of face masks on speech comprehension

An outstanding health-policy goal -until the development of a vaccine- is to mitigate the spread of SARS-CoV-2 in the population. It is unclear when such a vaccine will be widely available and how protective it will be. This means that for a long time to come, the most effective means for combatting the virus is the adaptation of human behaviour. Next to social distancing and hygiene practices, many countries recommend or even prescribe the use of face-masks, especially in situations when minimum distances cannot be upheld. A rarely noted side effect of this virologically meaningful measure is that it deprives interpersonal speech communication of an extremely important cue: the lip movements of the speaker. This visual information supports speech comprehension, especially in challenging listening situations (e.g. conversation in a noisy café). While this can be said in general also for normal hearing individuals, it applies even more strongly to individuals with hearing damage, i.e. approximately 1.3 billion humans worldwide according to estimates of the WHO from 2017. This disadvantage of these individuals through face masks has to be seen from two sides: 1) a qualitatively reduced speech comprehension, in particular by missing lip movements; and 2) an increase of the necessary listening effort as a compensatory consequence. Also in light of the fact that hearing damage is an important predictor for developing dementia in future, it is vital to quantitatively determine this putative disadvantage and to understand it ideally in functional terms. The goal of this Urgent-Funding project is to understand how occluded information of lip movements by the use of face masks affects overt speech-related processes (e.g. comprehension, subjective effort) as well as those inferred from neural data (e.g. tracking, physiologically based estimates of comprehension and effort).

The research project aimed to understand how wearing face masks, which block visual speech cues and potentially distort acoustics, affects people's ability to comprehend speech, especially in challenging listening conditions. Speech comprehension is vital for daily life and is already difficult for many, particularly those with hearing impairments, a group that includes about 1.3 billion people worldwide according to WHO. Lip movements help listeners, especially those with hearing difficulties, understand speech better by providing important visual cues. However, face masks, which have become widespread due to public health measures during the COVID-19 pandemic, remove these visual cues and may also impact the sound of speech. To investigate this, the project tested both young adults with normal hearing and older adults with varying degrees of hearing impairment. Participants were asked to listen to speech with and without face masks either only acoustically or with the speaker presented visually additionally, and in some cases, additional background speech was introduced to simulate more challenging listening conditions. Both brain activity and the participants' ability to understand the speech were measured to investigate the underlying processes. The results revealed that the challenge posed by face masks is a combination of blocked visual speech cues and possibly distorted acoustics, particularly in individuals with hearing impairments. For young adults with normal hearing, the loss of visual cues was the primary issue. The study also confirmed previous findings that the neural benefit of visual speech varies significantly between individuals. This individual ability to benefit from visual speech cues strongly predicted how much people relied on visual speech tracking in difficult audio-visual listening situations. Interestingly, this reliance was not correlated with hearing thresholds, suggesting that using visual speech as a compensatory strategy is not necessarily more common among those with hearing impairments. These findings have practical implications, particularly in healthcare, education, and professional settings where communication is crucial. Understanding the impact of face masks on communication can help shape better public health policies and communication strategies, especially for those with hearing impairments. Additionally, these insights could inform the development of new technologies or approaches to assist people in overcoming communication challenges in environments where face masks might continue to be used. In conclusion, while face masks are essential for public health, they present significant communication barriers, especially for individuals with hearing difficulties. This research highlights the importance of considering these challenges in public health policies and underscores the need for alternative communication methods to support those who rely heavily on visual speech cues.