The study involved 37 healthy adults between 18 and 25 years of age. Seventeen participants were assigned to the control group. They slept normally at home for a night. The other 20 participants were kept awake in a sleep lab for about 31 hours.
Then everyone performed an emotional face recognition task at about 4 p.m. Both groups returned home for a night of sleep. Then they repeated the task the next day.
The task involved the presentation of black and white photos of the same man. The images were taken from Dr. Paul Ekman’s Pictures of Facial Affect set. In the photos the man made happy, sad, angry and neutral expressions.
Each of the three emotional pictures was morphed to the neutral face using computer software. This produced a set of 10 images for each emotion representing an equal gradient of change.
For each emotion the 10 images were presented in random order on a laptop computer screen. Participants had to rate the strength of emotion for each face.
Results show that the ability to recognize angry and happy facial expressions was blunted in the sleep-deprived group. They were able to detect extreme emotions. But they struggled to detect expressions of moderate intensity. There was no change in the recognition of sad expressions.
These differences were most reliable and significant in women. The impairment was corrected by one night of recovery sleep.
The authors suggested that facial expressions may be the most significant visual cue in human communication. Abnormal face processing can lead to impaired social interactions.
They also wrote that accurate emotional face judgments are of critical importance for many professionals. Examples include emergency responders, medical staff and soldiers. This ability also is vital for new parents.
The results also suggest that healthy young women may be more sensitive to some effects of sleep loss. This may help explain why women are more likely than men to develop major depression.
Last year the Sleep Education Blog reported that being awake for 12 hours or more may impair the ability to recognize a familiar face. Read more about sleep deprivation.
Image by nebojsa mladjenovic