A recent study published in the journal Sleep suggests that the simple act of wearing an eye mask to block out light while sleeping can improve cognitive function the next day. In two experiments, the researchers found that participants who slept with an eye mask showed enhanced episodic memory encoding and alertness the following day.
As sleep studies continue to demonstrate, good sleep is vital for the healthy functioning of our brains and bodies. For example, too little sleep or a lack of quality sleep can negatively impact our alertness during daily activities. Studies also demonstrate that one driver of disrupted sleep is ambient light.
The sleep-wake cycle is regulated by the earth’s cycle of light and dark, with the morning sunlight signaling us to be alert and the darkness of night signaling us to fall asleep. But sunlight is not the only source of light that can impact our sleep — ambient sources of light like streetlights and light from electronics can also reach our retinas and affect our sleep.
“Moving to the United Kingdom meant not being able to sleep for a simple reason: houses in Cardiff don’t have shutters!” said study author Viviana Greco, a PhD candidate at Cardiff University Brain Research Imaging Centre and freelance associate editor at Researcher. “Most houses in Cardiff area have only curtains and even blackout curtains are not enough to provide complete darkness.”
“This was particularly problematic during the summer months when the sun rises as early as 4am, making it difficult to sleep. As sleep scientists, we understand the importance of getting enough sleep, and waking up at 4am every day was not ideal. We became then curious to know whether wearing an eye mask overnight to block ambient light could be an easy solution!”
Greco and her colleagues conducted two experiments to explore how wearing an eye mask that blocks ambient light during sleep might impact cognitive performance. While studies have suggested that eye masks can improve sleep among patients in intensive care units, Greco and associates wanted to study the effect of eye masks on regular sleep in the home.
The first study involved a final sample of 89 participants between the ages of 18 and 35. The study was conducted over two weeks. During the experimental week, participants spent 5 nights sleeping in their homes while wearing an eye mask and then took part in 2 days of testing. During the control week, participants spent 5 nights sleeping at home with no eye mask and then 2 days of testing.
The researchers found that participants showed better learning performance on a word-pair association task after wearing the eye mask. They also reacted faster on a psychomotor vigilance test that measured behavioral alertness and sustained attention. Together, this suggests that the sleep mask resulted in better episodic memory encoding and alertness.
A second experiment included 33 participants between the ages of 18 and 35 years old. This time, participants spent two nights sleeping with an eye mask (experimental procedure) and two nights sleeping with an eye mask with cutouts so that no fabric covered the eye region (control procedure). Participants slept at home with a digital light meter placed on their pillows and while wearing an EEG headband to examine their sleep stages.
The results replicated the finding from experiment 1, where participants showed better learning performance on the paired associative learning task after wearing the eye mask. Interestingly, participant sleep diaries did not reveal any differences in hours of sleep or self-rated sleep quality between the eye mask or control conditions.
The results did reveal, however, that better learning performance after wearing the mask was associated with longer slow wave sleep time. Thus, memory improvements after mask-wearing were predicted by time spent in slow wave sleep.
According to the synaptic homeostasis hypothesis, slow wave activity restores the brain’s ability to encode new information by downscaling synapses that have been strengthened during waking hours. Though their study was unable to measure this, the researchers suggest that the eye masks may have led to increased slow wave activity.
The study findings have real-world implications, the authors say, particularly since many everyday tasks, such as driving a car, require us to be alert and perform rapid responses.
“Wearing an eye mask overnight can be an effective and inexpensive solution for improving and benefit cognitive performance,” Greco told PsyPost. “Our results speak about improved reaction times and improved memory performance. The implications of our results are significant on many daytime tasks like driving a car or any educational or cultural context that requires learning.”
The study, “Wearing an Eye Mask During Overnight Sleep Improves Episodic Learning and Alertness”, was authored by Viviana Greco, Damiana Bergamo, Paola Cuoccio, Karen R. Konkoly, Kike Muñoz Lombardo, and Penelope A. Lewis.