Researchers from Zhejiang University, China, led by Jiaxin Gao, have shed light on the remarkable ability of the human brain to untangle speech from echoes, a feat that continues to baffle engineering solutions. In their study published in PLOS Biology, they investigated how our brains effortlessly decipher direct speech amidst echoing reverberations, a common occurrence in environments like online meetings and auditoriums.
Despite echoes lagging at least 100 milliseconds behind the original speech, which heavily distorts the sound, humans still grasp conversations with remarkable accuracy. Employing magnetoencephalography (MEG), the researchers monitored brain activity while participants listened to narratives both with and without echoes. They then compared these neural responses to computational models simulating two possible brain mechanisms: adaptation to the echo and separation of direct speech from its echo.
Surprisingly, participants maintained over 95% accuracy in comprehending the narrative, irrespective of the echo’s presence. The researchers found that cortical activity closely tracked changes in energy associated with direct speech, even amidst significant echo interference. While one model simulating neural adaptation partially explained observed brain responses, a more convincing explanation emerged from a model positing separate processing streams for direct speech and its echo.
Remarkably, this segregation persisted even when participants were instructed to focus on a silent film, suggesting that top-down attentional processes are not necessary for the brain to disentangle direct speech from echoes.
The implications of this research extend beyond mere comprehension in noisy environments. The ability to segregate speech from echoes aids in isolating specific speakers in crowded settings and enhances understanding in reverberant spaces. Moreover, the authors note the significance for automatic speech recognition, as echoes pose a formidable challenge that the human brain adeptly overcomes.
Source: Public Library of Science