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.

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You're sitting at the breakfast table, checking your email or reading last night's sports scores, and your spouse asks you a question -- and you don't respond. Then comes the inevitable: "Are you listening to me?" And you nod your head but really haven't heard a thing.

If this scenario sounds familiar, science has just provided you with the perfect excuse -- and it's not "selective hearing." Thanks to research recently published online in the journal Attention, Perception, & Psychophysics, you can blame it on "inattentional deafness."

A newly-identified phenomenon that's common in everyday life, inattentional deafness occurs when your attention and focus are placed on a visual task, so you tune out the sounds around you. For example, you may be immersed in the latest must-read bestseller and miss the announcement for your bus or train stop. You could be fiddling with a new cell phone app while crossing the street and not hear an approaching car. You could be driving down the street and glancing at a hot chick in a skimpy outfit but fail to notice the beeping of a truck backing out of a driveway.

When your mind is busy elsewhere, it seems to turn down the volume on other noises around you. "Inattentional deafness is not about where your eyes are, it's where your mind's eye is," says Nilli Lavie, a professor of psychology and brain sciences at the Institute of Cognitive Neuroscience at University College London.

In the study, Lavie and a colleague conducted a series of experiments on more than 100 volunteers who had perfectly normal hearing and vision. Participants were asked to wear headphones during the test to supposedly help them concentrate. In truth, though, the headphones sometimes unexpectedly produced an audible tone. 

Volunteers first did an easy task -- noticing the colors of two crossed lines on a computer screen. When asked, eight out of 10 remembered hearing the tone during this simple test.

But during a harder task that required more concentration -- identifying the larger of two crossed lines -- the results were reversed: Eight out of 10 missed hearing the same exact tone.

The findings suggest that "your perception of sounds depends not just on your sense of hearing but also on your ability to pay attention," explains Lavie, the study's lead author. "It's the first time that we've shown that people are not able to detect an ordinary tone if they're engaged in a task that demands full attention."

Hearing is thought to have developed as an early warning system that does not hinge on attention. So the British scientists were surprised to discover attention mattered: In this research, hearing abilities changed because of mental processing.

Inattentional deafness is the hearing equivalent of "inattentional blindness," a failure to see unexpected things when your brain is concentrating on something else. Body Odd has previously written about the Invisible Gorilla experiment, where people who were busy counting basketball passes often missed seeing the obvious -- a man in a gorilla suit crossing the court. 

And while they haven't looked at the mechanism that makes you deaf to the world around you, it likely works along similar lines to the ones that blind you. Lavie suspects the part of the brain responsible for interpreting sound is registering a weaker signal because it's involved in another task that's taking up all its attention.

Do you have any funny stories from your own "inattentional deafness"? Pray tell.

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