Researchers from Royal Holloway, University of London, found that more than two thirds of those eavesdropping on the women failed to notice a man chanting "I am a gorilla" repeatedly for 19 seconds over the conversation.
The study, published in the journal Cognition, was an example of how intense conversation can leave us 'deaf' to the world around us, the researchers said.
A famous study from 1999, in which people watching a basketball game failed to spot a man walk through in a gorilla suit and beat his chest, revealed how focusing on one thing can leave us "blind" to events happening right in front of us.
But this study is the first to show that hearing is similarly affected, the Daily Mail reported.
The researchers placed two men at a table in a room and two women at another table and recorded them talking about getting ready for a party.
Some of their conversation overlapped.
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Halfway into the recording, a man walked through the room, repeating the phrase "I am a gorilla".
The recording was then played to a group of volunteers.
Some listened to the women