Macquarie University hearing researchers have discovered how our brains learn to 'listen to the room', and how this can help us understand speech in noisy, echo-filled spaces.
Silent treatment: Senior author Distinguished Professor David McAlpine, pictured, ran the research using the Macquarie University, reverberation-free anechoic chamber.
The research, funded by the Australian Research Council and published online in eLife, looks at how we can unconsciously adjust to different kinds of background noise.
Building on earlier work that showed animals' brains quickly adapt to changes in sound levels, the new study is the first to show how humans adapt to echoey environments to improve their speech understanding.
The study placed volunteers with normal hearing in the University's anechoic chamber, a specially designed space that is free of reverberation.
Using recordings from real spaces, including an underground car park, a lecture theatre, and an open-plan office, the researchers simulated different levels of reverberation, or echo.
Participants listened to short speech commands in conjunction with background noise and reported what they heard.
It's important to recognise that listening is an immersive experience, shaped by our environments, our brains and how the two interact.
Senior author of the paper, Distinguished Professor David McAlpine, says participants improved at understanding speech over time, even in difficult spaces.
"What was surprising was that they learned best in the 'Goldilocks' zone, which are spaces with 'just the right' amount of echo — about 400 milliseconds of reverberation, which is typical of many modern spaces like lecture theatres," Professor McAlpine says.
"Environments with too much echo, like marble-filled lobbies or underground car parks, both made learning to listen much harder as did, counterintuitively, rooms with no echo at all.
"This sweet spot or 'Goldilocks' zone, seems to match the average reverberation of spaces we spend most of our time in.
"It's possible we've designed our buildings to fit our brains — or that our brains have adapted to these buildings."
Listening is more than hearing
First author of the study Dr Heivet Hernández-Pérez says hearing speech in a slightly echoey environment gives the brain time to adjust and recognise patterns.
Listening: Hearing researchers Dr Heivet Hernández-Pérez and Distinguished Professor David McAlpine, pictured, in the Australian Hearing Hub's anechoic chamber.
"It's not about remembering the room consciously. It's about your brain learning the structure of the environment and using that to make sense of speech, even without you realising it. Our ears hear, but our brains listen.
"They're constantly adapting through feedback loops, learning and changing on the fly."
As part of the study, the team used magnetic brain stimulation to briefly disrupt an area of the brain involved in learning.
Over the course of the 45-minute test, people got better at recognising speech because their brains were learning the 'sound of the room'.
When they did, participants' ability to adapt to different sound environments dropped significantly.
"This shows us there are specific brain circuits responsible for this kind of learning," Dr Hernández-Pérez says.
"Understanding how they work could help us develop better, more inclusive sound environments, whether we're talking about public spaces or personalised hearing technology.
"It's important to recognise that listening is an immersive experience, shaped by our environments, our brains and how the two interact.
"We're not just hearing sounds. We're hearing the world through those sounds."
Shaping technology and inclusive spaces
Professor McAlpine says the team's findings will also feed into the design of hearing and listening devices, such as hearing aids and headphones.
"Most hearing technology tries to eliminate all background noise and echo," Professor McAlpine says.
"But if some reverb actually helps people hear better, then we may be throwing out something that the brain finds useful."
The team is now designing new studies to explore how neurodivergent people and people with hearing loss experience reverberation, and whether their 'Goldilocks' zones are different from those of neurotypical listeners.
Distinguished Professor David McAlpine is Academic Director of Macquarie University Hearing.
Dr Heivet Hernández-Pérez is a Research Fellow in the Macquarie University Hearing Research Centre and the Macquarie University Department of Linguistics.
