How can you hear what someone is saying at a crowded party – even when they are halfway across the room? It’s all about the cocktail party effect.

The cocktail party effect refers to the ability of people to focus on a single talker or conversation in a noisy environment. For example, if you are talking to a friend at a noisy party, you are able to listen and understand what they are talking about – and ignore what other people nearby are saying. It’s basically a form of aural eavesdropping. By wearing two hearing aids, particularly two digital hearing aids that can communicate together instantaneously, people with hearing loss can fight the cocktail party effect. The interaction between the pair simply helps users better determine the location of a sound.

The cocktail party effect was first described by Colin Cherry, a British scientist, in the early 1950s. Cherry conducted a series of experiments to determine how people listen. In the first, he played back two different messages (voiced by the same person) through both ears of a set of headphones. He then asked the participants to write down one of the messages.

After some effort and concentration, they could, eventually, separate one of the messages from another. The real surprise, though, came in the second series of experiments. Here, the participants were played one message to the left ear and one message to the right ear (again voiced by the same person). Suddenly, they could separate the messages from each other - and even shift their attention between the two.