Impaired Ability to Recognize Facial Expressions is Linked to Sleep Deprivation

A study out of the University of Arizona Psychology Department found that a rough night’s sleep may impair your ability to read the room when it comes to facial expressions.

Published in Neurobiology of Sleep and Circadian Rhythms, the research reported that participants who were sleep deprived had a harder time recognizing happy and sad facial expressions than those who were well rested.

However, it is notable that sleep-deprived participants did not show any impairment in recognizing other emotional facial expressions like anger, surprise, fear, and disgust.  That may be because those expressions and emotions are more primitive, and they are wired differently in our brains to help us survive dangers.

Research was led by the UA professor of psychology, psychiatry, and medical imaging, Dr. William D.S. Killgore.

Social emotions like sadness and happiness do not indicate threat like anger and fear do, so they are emotions that are not as necessary for immediate survival.  When we are sleep deprived, we are more likely to dedicate all resources to recognizing only things that put us in immediate danger.

Dr. Killgore notes that even when you are sleep deprived, you should still be able to identify when someone is trying to harm you.  In that kind of situation, being able to read whether someone is happy or sad is not that important, so social emotions are put on the backburner when your body is trying to fight the effects of exhaustion.

Dr. Killgore collected data from previous research that focused on how sleep deprivation affects emotional, social, and moral judgements.

Fifty-four people were analyzed in this study.  They each were shown a photograph of the same man’s face expressing different degrees of emotions like sadness, anger, fear, happiness, disgust, and surprise.  The participants then had to determine which of those emotions was being expressed on the man’s face.

The images were intentionally somewhat ambiguous, using commonly confused expressions that were morphed and modified by a computer program.  For example, one expression may have shown 30% surprise and 70% sadness.  This was done to analyze the participants’ ability to recognize more subtle expressions.  A total of 180 images of blended facial expressions were shown in each session.

The baseline response to the photographs when well-rested were compared to their responses after one night of sleep deprivation.

The more obvious facial expressions, like a frown or grin, could be identified without any problem, regardless of how much sleep that person got the night before; however, tired participants had a tough time recognizing subtle expressions of sadness and happiness, even though their ability to identify other emotions was not impaired.

After a good night’s sleep, the participants had no problems recognizing those sad and happy expressions, immediately returning to baseline level after recovery sleep.

The difference between the two was not as significant as some might hope; however, it is enough evidence to suggest that long-term sleep deprivation could have a significant effect on social interactions.

Dr. Killgore notes that in this society, most people are not able to get the recommended seven to eight hours of sleep each night, with the average being less than six hours of sleep.  This could impair the ability to read common emotions and, therefore, interfere with daily interactions.  For instance, you may respond inappropriately to a person who is sad because you thought they were angry.  Social emotions are uniquely human, so not being able to identify those in other people could lead to some serious complications in everyday life.  You would be unable to read what your spouse or partner needs from you as well.

This research was built onto the existing work focused on how sleep deprivation affects the brain’s prefrontal cortex, which is responsible for making decisions, judgements, and using emotions.

An earlier study from Harvard found that sleep deprivation causes a disconnect between the prefrontal cortex and the amygdala, which is the part of the brain that helps you respond to emotions.

Essentially, these two parts of the brain control emotions and help us recognize those expressions on others, and sleep deprivation causes them to lose their communication.  The point of this study was to test that theory from the Harvard study, and Dr. Killgore is confident that it does.


Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development.


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