Jeanne Duffy of Brigham and Women's Hospital in Boston said 12 people took part in a one-month study in a sleep laboratory. Participants' sleep was cut back from 10-to-12 hours a night to fewer than 6 hours and the participants were then asked to search for differences in pictures on a computer screen.
The participants who had less sleep performed the task slower than the others, even if they didn't realize it, Duffy said.
"When they cut back on the amount of sleep that they're getting, especially if they do that on a regular basis, they may not realize how impaired they are by their own sleepiness," Duffy said.
The study was published in the Journal of Vision.
Notable deaths of 2014 [PHOTOS]