A new study is a good reminder that lifestyle changes don’t always need to be expensive or complicated to improve well-being. People who slept with an eye mask — which can go for as little as $5 online — showed improvements in cognitive skills like recall, word association, and reaction time, according to research published in the journal Sleep.
The boosts observed in memory and reaction times have broad implications, says the lead author of the study, Viviana Greco, a PhD candidate at Cardiff University Brain Research Imaging Center in Wales.
“For example, better learning could improve academic and professional performance, while faster reaction times could help in sports, driving, or other situations where quick responses are critical,” says Greco.
Participants Who Wore Sleep Masks Had Better Recall and Reaction Time the Next Day
Previous research has shown that ambient light can negatively influence both how long you sleep and the quality of that sleep, including how much deep or slow-wave sleep (SWS) you get, according to the authors. Even when you turn off all the lights in your bedroom, you may still be exposed to ambient light from your partner’s phone, for instance, or from a streetlight outside your window, or even the moon.
For this study, Greco and her colleagues designed two experiments to explore how wearing an eye mask to block light during overnight sleep might affect memory and alertness.
In the first experiment, 89 adults ages 18 to 35 wore an eye mask (the intervention) while sleeping for one week. After getting used to wearing the mask for the first five days, the participants underwent a series of lab tests to log their recall and reaction time for the final two days.
During the “control” week, participants underwent the same regimen but without a sleep mask.
Researchers found that the subjects who wore the masks performed better on a word-pair association task, which measures the ability to recall events and experiences, and on a psychomotor vigilance test that measures behavioral alertness and sustained attention. These results suggest that the sleep mask was associated with better episodic memory encoding and alertness, wrote the authors.
For the second experiment, 33 adult volunteers between ages 18 and 35 spent two nights sleeping with an eye mask (the intervention) and then two nights sleeping with an eye mask with cutouts so that no fabric covered the subjects' eyes (the control). This was intended to make sure the results weren’t impacted by the overall feeling of wearing a mask.
As with the first study, participants who wore the complete mask performed better on the paired word tasks.
Blocking Out Light May Reduce Disruptions to Circadian Rhythms
Both these studies were well-designed and executed, says Thomas Preston, PhD, a clinical assistant professor in the department of neurology at Stony Brook Medicine in Stony Brook, New York, who was not involved in the research.
“These findings are interesting, though not necessarily surprising. We’ve known for many years that large amounts of ambient light disrupts sleep cycles. It makes people less alert and makes it harder for people to function,” says Dr. Preston.
That may be because our body's internal clock, called the circadian rhythm, synchronizes important bodily processes including sleep, cognition, and health — all according to the day and night cycle, says Greco.
“Disruptions to our circadian rhythm, such as exposure to light at night, can impact memory and alertness. Additionally, it is widely recognized that a good night of sleep is beneficial for cognitive functions," she says.
Slow Wave Sleep: When the Body Restores and Repairs Itself
In the second study, participants also wore an EEG headband to track their sleep stages, and they were also asked to keep a sleep diary.
According to the participants’ sleep diaries, the mask didn’t make a difference in how long they slept or the quality of their sleep.
But the EEG headbands revealed that better learning performance after subjects wore the mask was positively correlated with spending more time in slow wave sleep (also called NREM sleep, or deep nonrapid eye movement sleep).
Slow wave sleep is when the body is in its most restful state. It’s called “slow wave” because brain waves are slowest during this phase of sleep, according to the Sleep Foundation.
It’s during this time that the body physically restores itself. Research suggests that up to 95 percent of human growth hormone is produced during slow wave sleep. Most adults spend between 10 and 20 percent of their time asleep in SWS.
High-Quality Sleep Is Associated With Improved Cognition
Existing evidence supports the connection between higher-quality sleep and improved cognition, and interrupted sleep can have the opposite effect, says Preston.
For example, people with obstructive sleep apnea (OSA), a condition in which people's breathing patterns change during sleep because of airway obstruction, perform more poorly on cognitive tests, says Preston. “In general, they have poorer learning and retrieval of new information, and they have poorer attention and psychomotor processing speed,” he says.
Sleep Aids That Block Out Light and Noise May Improve Function the Next Day
Although the results in both these small studies were statistically significant, the findings weren’t huge in either measure, says Preston. “In your daily life, you may or may not really notice a change. Wearing a mask to sleep won’t turn you into a cognitive superman or superwoman,” he says.
But the new research does add to existing evidence that blocking out ambient light improves sleep quality which, in general terms, is associated with improved cognition, says Preston. “Wearing a sleep mask is potentially a very useful thing to do to improve sleep. Just don’t expect gigantic effects,” he says.
Likewise, blocking out intermittent disruptive noise with ear plugs and or listening to “colored” sound – brown or pink noise, similar to white noise — can help improve sleep as well, says Greco.
For Better Sleep, Say Good Night to Your Phone
Too much time on phones, iPads, and computers close to bedtime can be a real problem for a lot of people, says Preston. “For example, research suggests that when you keep your phone on in your bedroom at night, you’re ‘sleeping with one eye open,’” he says.
In other words, you’re more likely to be vulnerable to alerting stimuli (like tones or a screen lighting up) if the alerting stimulus (your phone) is nearby. That disrupts sleep, he explains.
“I tell people who are having issues with getting enough sleep or quality sleep that the phone must be in another room, and it needs to be off. All screens should be off at least an hour before bed,” says Preston.
A consistent bedtime and waking time, in addition to avoiding alcohol and caffeine before bed, will also improve sleep, according to the Centers for Disease Control and Prevention (CDC).
Lots of little things done right may add up to a better night’s sleep, but don’t beat yourself up when things don’t go according to plan, says Preston. “Often, we put pressure on ourselves to be a top performer in every area, including sleep,” he says.
Preston recommends establishing a good pattern of getting ready for bed at night using the general principles of good sleep hygiene. “If you deviate on occasion, don’t stress about it. That’s probably going to make you toss and turn even more and may make it even harder to sleep,” he says.