Are you Angry or Happy? Sleep Deprivation Makes it Harder to Tell

In a paper recently published in the journal SLEEP (2010;33(3):335-342), a group of researchers from the University of California at Berkeley report a very provocative finding: being sleep deprived makes it harder to read emotions on strangers' faces.

Who they studied: 37 young (age 18-25), healthy adults who were randomly assigned to either total sleep deprivation (no sleep at all for one night) followed by two nights of recovery sleep or three nights of restful sleep. The group was mostly female (21/35) and, importantly, the authors did not report the ethnicities of the participants.

What they did: To measure ability to detect emotions, subjects were shown a series of pictures of a face that was either (a) Sad, (b) Angry, or (c) Happy. The intensity of the emotions on the face varied from "definitely neutral" to "definitely happy" (or angry or sad). All pictures were of the same person and were in black and white, taken from the standard set of faces developed by Ekman. Importantly, all subjects knew which emotion was being shown -- they were just supposed to rate how intense the emotion was. Presumably, if the rating was more neutral, they saw less of that emotion in the face.

What they found: Across all emotions, in general, the sleep-deprived group was less able to pick up on the intensity of the emotions used -- they were more likely to rate the faces more neutral overall. With respect to specific emotions, the effect was largest for the Angry and Happy faces. In both cases, both groups could identify the most extreme faces at the same rate, but those faces that were not extreme were generally rated as more neutral by those that are sleep deprived. All of these effects disappeared after 1 night of recovery.

What do the findings mean? After a night of no sleep, you tend to see other people's faces as less emotionally intense than if you had slept. And this difference will go away once you get a good night of rest. So if someone is very angry (potentially a dangerous situation), you are less likely to be able to tell. Also if someone is happy, you will be less likely to tell that as well.

Some questions that remain:

1. Since we know that certain cultures are more sensitive to facial emotions, how do these results apply across cultures?

2. Since the subjects in this study were all young, healthy college-aged people, how much of this also applies to adults over 25?

3. Since the only sleep deprivation condition was total sleep deprivation, how does this apply to partial sleep deprivation -- where you get less sleep than you need, but more than none at all?

Paper: Sleep Deprivation Impairs the Accurate Recognition of Human Emotions

Authors: Els van der Helm, MSc; Ninad Gujar, MSc; Matthew P. Walker, PhD 

Link: http://www.journalsleep.org/ViewAbstract.aspx?pid=27729