Acoustician Adam Vogel of University of Melbourne, Australia has found that one can make out how tired a person is just by listening to their voice.
He describes a novel method to acoustically analyze the effects of fatigue on the central nervous system as revealed through speech.
Those concerned with managing tiredness - such as workers, public safety officials - will benefit from the find, he said. It may also be a useful tool for monitoring fatigue in clinical trials where alertness is a key measured outcome.
18 young adults were provided speech samples (sustained vowels, reading counting and reading tasks) every two hours in the study.
Vogel and his colleagues looked at components of speech such as length of pauses and total time to complete a spoken task.
Results indicated that as fatigue progresses, speech slows and variations in pitch increase and tone diminishes.
The team concluded that we have less control over the muscles that produce speech as we become more and more tired.
"Although remaining awake for 24 hours is physically and mentally exhausting, it's actually a great way to make new friends," notes Vogel.
"Most of them just entertained themselves between testing by watching movies, reading or talking amongst themselves."
The study appears this month in The Journal of the Acoustical Society of America.