Most people would admit that eavesdropping can be engrossing, but many people don't realize how much attention it commands.
A new study found that people concentrating closely on a conversation are "deaf" to other surrounding sounds.
UK researchers created a lifelike, three-dimensional auditory scene, containing one conversation between two men and another between two women.
Halfway through the recording, researchers introduce a "gorilla man" who walks through the scene repeating the phrase "I'm a gorilla!" for 19 seconds.
Researchers found that participants listening to two women chatting were so captivated by the conversation that they failed to notice that chanting gorilla man speaking over the women's discussion.
Specifically, more than two thirds of participants eavesdropping on the women failed to notice the man, who had repeated "I'm a gorilla" for 19 seconds.
However, people who were concentrating on the men's conversation were much better at detecting the "gorilla man".
Lead author Dr. Polly Dalton from the Department of Psychology at Royal Holloway, University of London said that the latest study serves as an example of how intense conversation can leave us "deaf" to the world around us.
"We're much less aware of the world around us than we tend to think" Dalton said in a statement. "This research demonstrates that we can miss even very surprising and distinctive sounds when we are paying attention to something else."
A famous experiment in 1999 also found that most people watching a basketball game failed to spot a man who walked through the game in a gorilla suit beating his chest, revealing that focusing on one thing can also leave us "blind" to events happening right before our eyes.
"The 'invisible gorilla' effect, where people fail to see a person in a gorilla suit walking through a basketball game, is now quite well-known. Our study provides the first demonstration of a similar 'silent gorilla' effect in hearing," Dalton said.
"We were surprised to find such extreme effects with a listening task, because people often think of hearing as an 'early warning system' that can alert us to unexpected events that occur out of sight," she added.
"The fact that a lack of attention can cause people to miss even distinctive and long-lasting sounds questions this view. This has real-world implications in suggesting, for example, that talking on your mobile phone is likely to reduce your awareness of traffic noises."