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.
As much as 20 percent of car accidents can be blamed on sleep deprivation, according to the National Sleep Foundation. Lack of sleep is also associated with chronic diseases such as diabetes and obesity.
Sleep deprivation can be particularly dangerous for jobs including pilots, long-distance drivers or deployed military service members, said Brown.
In fact, LaJambe said the decision to research voices came from a discussion with Malcolm Brenner, an investigator with the National Transportation Safety Board.
For years, Brenner has analyzed pilots' voices on black boxes recovered after airplane crashes. Part of LaJambe and Brown's research looked into pilots' voices to detect any signs of fatigue.
"You can get a pretty good recording from pilots," said LaJambe.
But that's after the fact, LaJambe added. Real time analysis of a pilot's voice to screen for sleep deprivation would be more beneficial, she said.
"If the air traffic controller had a device that could have analyzed the pilot's voice in real time, she would have seen that he sounded sleep deprived," LaJambe said about one recording she heard.
This potential type of screening tool might be applicable to other occupations, as well, and could help judge whether an employee is potentially fit for duty, Brown said.
"If we can figure out precisely how these voice changes occur, then we could make a device that could discriminate the differences and tell what degree of fatigue the speaker is suffering," said Brown. "The fact that you sound sleepy probably means you are."
While the lab's preliminary research is still under publication review, Brown said those who are told they sound tired shouldn't brush it off. In fact, he said, the lab is now trying to find out whether people can truly hear how tired someone can be.
"Right now, we're trying to see an average person can detect the speech differences in those normal or sleep deprived," said Brown. "Because although some of us might sound tired, the degree may not be so clear to the human ear."