Sara Carta & Giovanni Di Liberto
Imagine you are at a crowded cocktail party. People are coming and going, yet you can follow your friend as they share some juicy gossip. The fact that you can follow what they are saying is down to your brain performing complex operations amid all the noise. Out of all the sound waves reaching your ears, it successfully isolates the one of interest while filtering out the rest.
Trying to understand how the brain does this has occupied auditory neuroscientists since the 1950s, when British cognitive scientist Colin Cherry coined the term “the cocktail party problem”. Early experiments asked volunteers to listen to two speeches simultaneously but repeat only one aloud. Cherry found that listeners could follow the pre-selected message remarkably well, despite both speeches playing at the same time, one in each ear. In contrast, they recalled very little of the other message.
These experiments laid the foundation for selective attention research. However, only in the past 15 years have scientists studied this phenomenon in experiments reflecting the complex ways we listen in the real world, using non-invasive technology like electroencephalography (EEG) to track brain activity as speech unfolds.
In a 2014 study, neuroscientists found that within 200 milliseconds of hearing someone speak, the brain favours the conversation being focused on over all other noise. This prioritised attention shows up most markedly in secondary brain areas such as the superior temporal gyrus, which piece together sounds into meaningful speech.
Yet real-life listening is rarely static. In everyday scenarios, we repeatedly switch our auditory attention — when hearing our name across a room or when a door slams. What happens in that brief moment when we stop listening to one person and turn our attention to another? Does the brain switch instantly, or does it briefly process both?
We investigated these questions in our latest study with colleagues from the Eriksholm Research Centre in Denmark, funded by hearing aid manufacturer Oticon.
Consider being focused on your friend’s voice when another familiar voice reaches your awareness: your partner secretly telling someone about a surprise gift for you. Your attention shifts immediately to your partner, while you maintain the appearance of listening to your friend.
When testing such scenarios, we found something striking. During this reorienting phase, the brain does not simply drop one voice and turn to the other. Instead, for a short period of between one and two seconds, the neural signals associated with both voices overlap. The brain starts tuning into the new speaker before completely letting go of the old one, maintaining a smooth “attention continuum”.
These insights carry important real-world applications. Traditional hearing aids often favour sounds coming from in front of the listener. Using enhanced attention-decoding techniques, future devices could be neurally steered to enhance the speaker currently attended to, switching dynamically between different voices almost in real time.
Ultimately, understanding how the brain manages these rapid shifts brings us closer to unravelling how successful communication happens — at cocktail parties and everywhere else.