Editor's Note: Don't read the text below until you watch the video above and take the "selective attention" test -- it's harder than you think!

Watching a movie. Listening to a debate. Eavesdropping. Whatever the situation, when we pay close attention to spoken words, we can become "deaf" to other sounds--even ones that come from a guy in a goofy gorilla suit, new research suggests.

Psychologists have long known that selective attention (concentrating closely on one particular thing) affects the way you perceive the surrounding world.

This was demonstrated in dramatic fashion in the celebrated "invisible gorilla" experiment. For the research, psychologists Dr. Daniel Simons and Dr. Christopher Chabris asked study participants to watch a fast-paced video in which a group of people pass a basketball and to count how many times certain people tossed the ball. Actually, you try it (watch the video above).

Did you notice the gorilla in the room? In the middle of the video, a person in a gorilla suit walks into the frame--a seemingly obvious intrusion that was noticed by only about half of the participants in Dr. Simons' study. It wasn't that the participants weren't paying attention but their selective attention had caused inattentional blindness.

Now a new study shows that this same phenomenon occurs with hearing. For her "silent gorilla" study, psychologist Dr. Polly Dalton of the Royal Holloway-University of London asked study participants to listen to two recorded conversations--one between two men and another between two women. In the midst of the conversations, a male voice repeated the phrase "I'm a gorilla" for 19 seconds (you can listen to a demo on Dr. Dalton's website).

The "gorilla man" didn't go completely unnoticed. About 90 percent of study participants said they heard it when listening to the men’s conversation--but only 30 percent noticed the intrusive voice when listening to the women’s conversation, Dr. Dalton told The Huffington Post in an email.

"This is nothing to do with women’s conversations being inherently different from men’s," Dr. Dalton said. "In fact, the men and women were all talking about preparing for a party, so there was no difference in the subject matter. Instead, we think that people noticed the gorilla when attending to the men’s conversation because the gorilla himself was male, so he was relevant to the task that those participants were carrying out."

The bottom line, Dr. Dalton said, is that even seemingly obvious distractions can be missed when attention is focused elsewhere--and that this is true whether the distraction is visual or aural in nature.

"The most interesting finding from this research is just how strong these effects of attention can be," she said. "Most of our participants found it hard to believe that they could have missed such a surprising and distinctive sound."

Dr. Dalton's study, conducted with research associate Nick Fraenkel, is slated for publication in the journal Cognition.

Also on HuffPost: