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Did he just say he's a gorilla?

You've heard about the elephant in the room, which no one wants to talk about. Now new research describes a gorilla in the room, which not everyone seems to hear.

For the first time, a study has confirmed the existence of "inattentional deafness." This is "when the absence of attention causes people to miss sounds that are otherwise easily detectable," says study author Dr. Polly Dalton, a senior lecturer in cognitive psychology at Royal Holloway, University of London.

In this study, appearing online in the journal Cognition, Dalton and co-author Nick Fraenkel asked 45 people aged 16 to 47 to listen to a recording on headphones. Half of the participants were told to pay attention to the two women talking in the recording, while the others were told to tune in to a conversation between two men.

Halfway through the recording, a man's voice is heard repeatedly saying "I'm a gorilla" for 19 seconds.

Participants were later asked if they heard anything unusual. To hear what the audio sounded like, click here

While 10 percent of the people listening to the men's voices failed to detect the "gorilla," 70 percent of the volunteers listening to the women's voices didn't hear it.

Afterward when researchers explained the study, "most of our participants found it hard to believe that they had missed such an unusual and distinctive sound, particularly given that it lasted for 19 seconds," says Dalton.

The research was modeled after a classic psychology study of "inattentional blindness."

This "invisible gorilla" study found that when people were focused on a visual task -- watching a video and counting the number of basketball passes made by one team --  they failed to notice someone walking across a basketball court dressed in a gorilla suit.

Dalton and Fraenkel monkeyed around with this concept replacing the visible gorilla with an auditory one to see if it would also go undetected.

In a second version of the experiment with 50 different volunteers, the male voice saying "I'm a gorilla" walked closer to the two women talking.

There was even more "inattentional deafness" in this scenario because 35 percent of participants focused on the men's conversation failed to hear the "gorilla" and 55 percent of volunteers concentrating on the women's discussion missed it.

"I think the most surprising aspect of the findings was just how strong the effects of attention could be," points out Dalton. When attention is lacking, it can leave people "deaf" to sounds or "blind" to visual images they would otherwise hear or see. 

One real-life example of inattentional deafness is when you're sitting in a restaurant with a friend, and two people are having an interesting conversation at a nearby table. But you've completely missed everything your friend has been saying to you because you've been listening in -- eavesdropping, really -- to the others' talk. 

Dalton suspects inattentional deafness happens because the brain is prioritizing the signals when concentrating on one task, but it filters out irrelevant information to avoid being distracted.

But don't go blaming inattentional deafness the next time you hear the words "Please, take out the garbage." That's usually a deliberate failure between your ears known as selective hearing, or only hearing what you want to hear.