Summary: Sleep deprivation results in a reduced ability to correctly read the emotional facial expressions of others, a new study reports.
Source: Uppsala University
A new study from Uppsala University shows that young adults when sleep-deprived evaluate angry faces as less trustworthy and healthy-looking. Furthermore, neutral and fearful faces appear less attractive following sleep loss.
The findings are published in the scientific journal Nature and Science of Sleep.
Using eye-tracking, a sensor technology that can detect what a person is looking at in real time, researchers from Uppsala University in Sweden performed an experiment on 45 young men and women to examine how acute sleep loss affects the way humans explore and evaluate happy, fearful, angry and neutral faces.
The participants spent one night with no sleep at all and one night with an eight-hour sleep opportunity. Their eye movements were measured in the mornings following both nights.
“When sleep-deprived, our research subjects spent less time fixating on faces. Since facial expressions are crucial to understanding the emotional state of others, spending less time fixating on faces after acute sleep loss may increase the risk that you interpret the emotional state of others inaccurately or too late,” says Lieve van Egmond, first author and PhD student in the Department of Surgical Sciences at Uppsala University.
“The finding that sleep-deprived subjects in our experiment rated angry faces as less trustworthy and healthy-looking and neutral and fearful faces as less attractive indicates that sleep loss is associated with more negative social impressions of others. This could result in less motivation to interact socially,” says senior author Christian Benedict, Associate Professor of Neuroscience.
“Our participants were young adults. Thus, we do not know whether our results are generalizable to other age groups. Moreover, we do not know if similar results would be seen among those suffering from chronic sleep loss,” says Lieve van Egmond.
How Sleep-Deprived People See and Evaluate Others’ Faces: An Experimental Study
Background: Acute sleep loss increases the brain’s reactivity toward positive and negative affective stimuli. Thus, despite well-known reduced attention due to acute sleep loss, we hypothesized that humans would gaze longer on happy, angry, and fearful faces than neutral faces when sleep-deprived. We also examined if facial expressions are differently perceived after acute sleep loss.
Methods: In the present, within-subjects study, 45 young adults participated in one night of total sleep deprivation and one night with an 8-hour sleep opportunity. On the morning after each night, an eye tracker was used to measure participants’ time spent fixating images of happy, angry, fearful, and neutral faces. Participants also evaluated faces’ attractiveness, trustworthiness, and healthiness on a 100-mm visual analog scale.
Results: Following sleep loss, participants struggled more fixating the faces than after sleep. The decrease in total fixation duration ranged from 6.3% to 10.6% after sleep loss (P< 0.001). Contrary to our hypothesis, the reduction in total fixation duration occurred irrespective of the displayed emotion (P=0.235 for sleep*emotion interaction) and was also present for the upper (P< 0.001) but not the lower part of the faces (except for the lower part of angry faces). Overall, faces were evaluated as less trustworthy (− 2.6 mm) and attractive (− 3.6 mm) after sleep loss (p< 0.05).
Discussion: Facial expressions are crucial for social interactions. Thus, spending less time fixating on faces after acute sleep loss may come along with several problems for social interactions, eg, inaccurate and delayed judgment of the emotional state of others. In addition, more negative social impressions of others may lead to social withdrawal in sleep-deprived humans.