Speech processing in an echogenic environment. Credit: Jiaxin Gao (CC-BY 4.0, creativecommons.org/licenses/by/4.0/)
Echoes can make speech more difficult to understand, and removing echoes in an audio recording is a notoriously difficult engineering problem. The human brain, however, appears to successfully solve the problem by separating sound into direct speech and echo, according to a study published in Biology PLOS by Jiaxin Gao of Zhejiang University, China, and colleagues.
Audio signals from online meetings and auditoriums that are not properly designed often have an echo that lags at least 100 milliseconds behind the original speech. These echoes significantly distort speech, interfering with the slowly varying sound characteristics most important for understanding conversations, but people still reliably understand echogenic speech.
To better understand how the brain allows this, the authors used magnetoencephalography (MEG) to record neural activity while human participants listened to a story with and without an echo. They compared the neural signals to two computer models: one simulating the brain “adapting” to the echo, and another simulating the brain “separating” the echo from the original speech.
Participants understood the story with over 95% accuracy, regardless of echo. The researchers observed that cortical activity follows the energetic changes associated with direct speech, despite the strong interference of the echo. The simulation of neural adaptation only partially captured the observed brain response: neural activity was best explained by a model that divided the original speech and its echo into distinct processing streams.
This remained true even when participants were asked to direct their attention to a silent film and ignore the story, suggesting that top-down attention is not necessary to mentally separate direct speech and its echo.
Researchers say that auditory stream segregation may be important both for distinguishing a specific speaker in a crowded environment and for clearly understanding an individual speaker in a reverberant space.
The authors add: “Echoes strongly distort the sound characteristics of speech and create a challenge for automatic speech recognition. The human brain, however, can separate speech from its echo and achieve reliable recognition of echogenic speech. »
More information:
Gao J, Chen H, Fang M, Ding N (2024) Original speech and its echo are separated and processed separately in the human brain, PLoS Biology (2024). DOI: 10.1371/journal.pbio.3002498
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Quote: A study on neuronal activity shows that the brain processes direct speech and its echo separately (February 15, 2024) retrieved February 15, 2024 from
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