Science Backs Statement: 'You Sound Tired'

March 3, 2011— -- You might think a cup of coffee or a quick walk before heading to your job will cover up your exhaustion from long working hours and little sleep.

That is, until your co-worker outs you by saying, "You sound tired."

Although it's a common phrase used to describe someone who might sound lethargic, many researchers say a closer look into how someone sounds can reveal how dangerous a sleep-deprived person might be.

Researchers at a Pennsylvania State University psychology lab are going beyond what the human ear can detect to measure how changes in speech could detect sleepiness. They found everything from voice inflection to letter pronunciation can indicate how tired you are and whether you may be better off sitting out of work than trying to stay productive.

In one study at the lab, researchers compared the speech of a small group of normal students with groups that were sleep deprived for 36 hours and 48 hours. They found the longer the students stayed awake, the more likely the analysis showed dramatic changes in energy, speech patterns and pronunciation.

"Police" sounded more like "Bolice." Higher energy letters such as T, P and K sounded more like D, B and G, respectively.

"Just the simple letter D tends to change as a person gets tired," said Frederick Brown, researcher and associate professor of psychology at Pennsylvania State University. "And how soon or how delayed they are when try to say it seems to be different than when they're wide awake."

Some of the changes researchers found may be unclear to the normal human ear, said Cynthia LaJambe, a visiting scientist and sleep researcher at Pennsylvania State University.

"We don't know if [sounding tired] means there's a handful of precise speech indicators of sleepiness, or whether [a person is finding] some general change in speech," said LaJambe.

The lab's analysis found that a sleep-deprived voice can suggest anything from fatigue to exhaustion that can result in dangerous behavior.