Imagine you're at a party. The room is packed, people are coming and going, and you barely hear your friend relaying that juicy gossip about the date he had last week.
The fact that you can still follow what he's saying is thanks to yourbrain, which performs very complex operations amidst all that noise. Out of all the sound waves reaching your ears, it successfully isolates the one that interests you, while filtering the rest.
Trying to understand how the brain does this has kept auditory neuroscientists busy since the 1950s, when British cognitive scientistColin CherryIt first coined the expressioncocktail effect(“The cocktail party problemAccording to the original English text (as cited):
This effect was initially studied in experiments in which volunteers were asked to listen to two speeches simultaneously - but then repeat aloud only one of them. Cherry discovered that listeners were able to follow and repeat the pre-selected message with remarkable accuracy, despite both speeches being played simultaneously, one in each ear. In contrast, they remembered very little of the other message.
These experiments laid the groundwork for decades ofResearch on selective attentionBut it was only in the last 15 years that scientists began to study this phenomenon in experiments that more closely resemble the complex and multifaceted way we hear in the real world — using technology that precisely monitors brain activity as speech unfolds.
The most common non-invasive option,electroencephalography(EEG), uses what resembles a swimming cap equipped with tiny sensors. These sensors measure very rapid changes in the electrical activity of populations of neurons (nerve cells in the brain) with a precision of milliseconds.
In a2014 study, neuroscientists discovered that within 200 milliseconds of hearing someone speak, the brain prioritizes the conversation the person is focused on over all other noises. This prioritized attention is more pronounced insecondary cerebral areassuch as theUpper Temporal Turn, who are responsible for organizing the sounds we hear into meaningful speech.
This suggests that our brain, when attentive, is not just amplifying the voice of the person we are listening to, but helping us understand their words while filtering out all other conversations and background noises.
Alternation of Attention
The original problem of the "cocktail party effect" did not investigate the full range of auditory experiences people have, which are often much less static. In everyday life, we repeatedly alternate and reorient our auditory attention — for example, when we hear our name called from across a crowded room or when a door slams.
But what happens in that brief moment when we stop listening to one person and shift our attention to another? Can the brain switch from one voice to another instantly, or does it need to process both for a brief moment? These were the questions we explored inour latest study.With colleagues fromEriksholm Research CentreIn Denmark, which is funded by Oticon, a Danish manufacturer of hearing aids.
Clarifying how the brain handles these rapid shifts in attention can help explain why some conversations are easy to follow, while others become difficult, especially in noisy environments.
Back to the party: there you are, focused on your friend's voice as he or she reveals the identity of his or her latest partner. But then another familiar voice suddenly catches your attention. Your partner (secretly) tells a friend about the surprise birthday gift he or she is planning for you. Your focus immediately shifts to your partner's voice, while you still give the impression of listening to your friend.
When we tested this scenario in our laboratory,We discovered something impressive.During this shift in attention, the brain doesn't simply discard one voice to focus on another. Instead, for a brief period of one to two seconds, the neural signals associated with both voices overlap. In other words, the brain begins to tune into the new speaker before it has completely disconnected from the previous one.
This mechanism can help explain how we navigate the ever-changing soundscape around us, shifting our attention from one voice or sound to another while still retaining enough information about the previous interlocutor to make the transition seamless. This efficient processing strategy could be described as the brain maintaining a "smooth attention continuum."
Improvement in the design of hearing aids?
These discoveries have some important real-world applications. For instance, traditional hearing aids are often designed to prioritize sounds coming from in front of the listener, which is obviously limiting in many situations.
But, using advanced techniques ofDecodification of AttentionBy 2050, hearing aids could beneurotically controlledNot only to highlight the speaker to whom attention is focused at the moment, but also to switch between different speakers, almost in real-time, as the listener's attention is dynamically reoriented.
In a more general sense, understanding how the brain changes, retains, and combines information from different speakers can give us a clearer picture of how attention shapes what we ultimately hear, understand, and remember.
The approach presented in our study may be particularly useful for studying how attention strategies vary among individuals, especially in noisy environments — and for relating these differences to the mental effort they employ to follow and understand speech.
Ultimately, this brings us closer to understanding how the brain makes successful communication possible — in parties and elsewhere.
Sara Carta received funding from the William Demant Foundation and Taighde Éireann – Research Ireland.
Giovanni Di Liberto receives funding from the William Demant Fonden and Taighde Éireann – Research Ireland. He is also supported by Research Ireland in ADAPT, the Research Ireland Centre for AI-Driven Digital Content Technology at Trinity College Dublin.