The market for wearable sleep trackers continues to grow, but did you know that tracking your sleep might actually be doing more harm, than good? In recent years, several studies have demonstrated that our perception of sleep quality can have a measurable impact on cognitive performance, as well as how alert or sleepy we feel. Discover why these findings relate to sleep tracking and discover how we might be able to harness these effects to influence our health and cognitive performance.
20 Years Of Wearable Devices
I’ve used some kind of wearable device for almost 20 years. I started out with a simple wrist-worn heart rate monitor to record my cycling training. Subsequently, I’ve lost count of the number of wearables I’ve owned, and these devices have evolved from merely being a training tool, to become part of my everyday life. I purchased my first wearable with a sleep tracking feature shortly before our second child was born. He wasn’t a great sleeper.
What Good Is Tracking If Sleep Is Out Of Your Control?
Each morning, as soon as my alarm had blasted me into a state of semi-consciousness, I pressed the button to illuminate the screen of my watch and assessed the damage. The device left me under no illusion that my sleep quality and duration was anything other than atrocious. One evening, just before I settled down for what I anticipated to be another restless night, I had a revelation. Sleep tracking was useless because there was nothing I could do to improve my sleep during that particular season of my life. The knowledge of how bad my sleep was only made me feel worse. Consequently, while I continued to track my sleep, I stopped looking at the results, and I was surprised to notice how much better I felt.
I continue to track my sleep and, thankfully, since our kids have grown older, my sleep is less disrupted than it used to be. I find that measuring my sleep is a useful tool to keep me accountable. For example, I can’t trick myself into thinking that I’m immune to the effects of alcohol and caffeine, when I can see the impact on my sleep so clearly in the morning. I also use research-grade wearable sleep trackers as part of my academic studies. However, in recent years, I’ve become more aware of some potential negative, unintended consequences of sleep tracking.
The word “placebo” is derived from the Latin phrase for “I shall please” and typically refers to treatment without an active therapeutic effect. For example, studies reveal that a saline (salt-water) injection, given in full view of a patient, can result in pain reduction equivalent to receiving 6–8 mg of morphine (providing the patient believes that they are receiving morphine)1. The placebo effect also appears to be able to multiply the efficacy of active treatments, with some studies suggesting that the placebo effect could account for 50% of a drug’s effectiveness2.
Placebos can be spoken about in derogatory terms, as tricks, or simply a means to provide an experimental control. However, the placebo effect is a potent force and can be classified as a measurable ‘brain event’ with powerful consequences3.
Why Our Mindset Matters
In 2014, another group of researchers demonstrated that the placebo effect extends beyond drugs and medications into everyday life, particularly concerning sleep and cognitive performance4. Participants in the study began by taking part in a lesson on sleep quality and cognitive performance. The participants were told that, on average, normal adults spend between 20% – 25% of their sleep time in REM (Rapid Eye Movement) sleep. They were then told that people whose sleep features less 20% REM perform worse in learning and memory tests, but people who spend more than 25% of their time in REM sleep perform better.
The participants were then assessed with a measurement system. They were told that this system could accurately determine the amount of REM sleep they had experienced, the previous night. Following this measurement, the participants were randomly assigned to receive either false feedback about the amount of REM sleep they experienced, or be part of a control.
Participants in the ‘above average’ feedback group were told they had spent 28.7% of their total sleep time in REM. Participants in the ‘below average’ feedback group were told they had spent only 16.2% of their time in REM sleep. The researchers were able to predict the participant’s scores in a cognitive test, designed to assess working memory and word association capabilities, based on whether they were in the above average, or the below-average fake feedback group. These findings demonstrated that the participant’s mindset concerning whether they had experienced above or below average proportions of REM sleep influenced their performance in both positive and negative directions, regardless of the real amount of REM sleep.
Inaccurate Feedback About Sleep Efficiency Influences Sleepiness & Performance
In 2018, a study investigated the role of false feedback with wearable devices5. The authors of the study paper recruited a group of participants who all suffered clinically significant insomnia. Following a baseline assessment, participants were assigned to one of two groups. Both groups were issued with wearable sleep-tracking devices, featuring a touchscreen display which could provide feedback about the previous night’s sleep efficiency. The devices were programmed to provide false feedback to both groups, regardless of actual sleep efficiency, but one group received positive feedback, while the other group received negative feedback.
The devices for the positive false-feedback group received the message: “Your sleep efficiency was 91.4% this is in the range of VERY GOOD sleep quality”. The devices for the negative false-feedback group received the message: “Your sleep efficiency was 61.4% this is in the range of VERY POOR sleep quality”.
The participants in the negative feedback group exhibited impaired cognitive performance in terms of decreased alertness, and increased sleepiness and fatigue, relative to the positive feedback group. In contrast, the positive‐feedback group displayed a greater increase in positive mood and alertness throughout the morning, as well as less sleepiness and fatigue.
The Unintended Consequences Of Sleep Tracking
Together, these findings highlight the powerful influence of the perception of sleep phases and sleep efficiency on both our performance and how sleepy and fatigued we feel. This has important implications as many wearable devices claim to provide objective measures of sleep quality and phases (e.g. REM vs NREM sleep), as well as duration. Potentially, the combination of increasing public awareness of the importance of adequate sleep, growing knowledge about the role of REM and NREM sleep, coupled with potentially inaccurate feedback about sleep from wearable devices, could result in unintended consequences.
Better Not To Know?
If your sleep tracker informs you that your sleep was better than it actually was, maybe that’s not a bad thing (providing you are getting at least seven hours of sleep per night). However, if your wearable provides indicates that your sleep was worse than it was in reality, it may result in you performing below your potential and feeling unnecessarily sleepy and fatigued.
I’m still an advocate for sleep tracking. It can be a helpful tool to measure sleep duration and monitor changes, providing the device is reasonably accurate. However, we should all likely be more cautious about how accurate our sleep tracking devices are, how much we read into the results, and consider that sometimes it might be better not to know.
- Levine JD, Gordon NC, Smith R, Fields HL. Analgesic responses to morphine and placebo in individuals with postoperative pain. Pain. 1981;10(3):379–89.
- Kam-Hansen S, Jakubowski M, Kelley JM, Kirsch I, Hoaglin DC, Kaptchuk TJ, et al. Labeling of Medication and Placebo Alters the Outcome of Episodic Migraine Attacks Slavenka. Sci Transl Med [Internet]. 2014;6(218):1–7.
- Benedetti F. How the doctor’s words affect the patient’s brain. Eval Heal Prof. 2002;25(4):369–86.
- Draganich C, Erdal K. Placebo sleep affects cognitive functioning. J Exp Psychol Learn Mem Cogn. 2014;40(3):857–64.
- Gavriloff D, Sheaves B, Juss A, Espie CA, Miller CB, Kyle SD. Sham sleep feedback delivered via actigraphy biases daytime symptom reports in people with insomnia: Implications for insomnia disorder and wearable devices. J Sleep Res. 2018;27(6).