Sleep-Deprived? You Might Sound Drunk

July 14, 2008 -- Lack of sleep alters the brain to such a degree that it can be heard in the way a person speaks, according to a new study that found sleep-deprived people sound almost drunk.

Bystanders might describe this type of speech as "tired-sounding" or "slurred," but experts studying the phenomenon say those descriptions aren't quite accurate.

"Slurred speech is an extreme form of unclearly articulated speech," lead author Suzanne Boyce told Discovery News.

"The differences we pick up are much less extreme, but they go in the same direction," added Boyce, a professor in the Department of Communication Sciences and Disorders at the University of Cincinnati. "We'd call it 'faintly blurred,' rather than 'slurred,' speech."

Boyce and her team theorized that the differences between the speech of people lacking sleep and those who had a good night's rest would be comparable to the differences between conversational and "clear" speakers.

"Clear" speech occurs when a person articulates or even over-emphasizes syllables, words and phrases -- such as when addressing a formal gathering, talking to people who are hard of hearing or for whom the spoken language is not their native tongue.

A word like "police," for example, might sound more like "blees" in conversational speech, but like "poe-lees" in clear speech.

Boyce explained that "the process is largely subconscious," but when people articulate more "they add more acoustic information bits to the acoustic signal." Computers can then detect these bits of information and note "landmarks," such as marking the puff of air released by the mouth when producing "t" or "k" sounds.

The researchers documented these changes and then applied the same analysis to recordings of test subjects who read sentences aloud and were asked to give driving directions approximately 10 hours since last sleep, then 34 and, finally, 58 hours.