Serious injuries involving pedestrians wearing headphones have more than tripled since 2004, a U.S. study showed.

Researchers from the University of Maryland found that people often were hit by vehicles because their music blocked out horns or sirens alerting them to danger.

In 70 percent of cases, the headphone-wearing pedestrians died as a result of the injuries they sustained from being hit by traffic.

The researchers studied the data of 116 accidents involving pedestrians wearing headphones between 2004 and 2011. The number of incidents rose from 16 in 2004 to 47 in 2011.

"Everybody is aware of the risk of cell phones and texting in automobiles, but I see more and more teens distracted with the latest devices and headphones in their ears," lead author Dr. Richard Lichenstein said. "Unfortunately, as we make more and more enticing devices, the risk of injury from distraction and blocking out other sounds increases."

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    The study, published in the journal Injury Prevention, found that young men were most at risk, with 68 percent of the 116 victims being male and 67 percent under the age of 30.

    Lichenstein and his team said that the distraction of the music causes "inattentional blindness," when multiple stimuli fed to the brain divide its mental resource allocation.