Author: Joshua Payne
Editors: Junyu Zheng, Ian Cho
Artist: Kyra Wang
Do you ever find yourself feeling sharp and focused in the morning, only to hit a slump in the afternoon? Or perhaps you notice a burst of creativity in the evening after a long day? Our bodies' natural rhythms drive these fluctuations in energy, mood, and cognitive performance. By understanding these rhythms, we can begin to use a powerful strategy that boosts productivity, enhances well-being, and allows us to make better decisions throughout the day. By aligning our activities with our biological clocks, we can unlock our full potential and lead more fulfilling lives.
To illustrate the impact of our daily rhythms, a 2011 study by two Cornell University sociologists, Michael Macy and Scott Golder, studied more than 500 million tweets from 2.4 million users in eighty-four countries over two years. The researchers fed the posts into a computerized text-analysis program called LIWC (Linguistic Inquiry and Word Count) that evaluated each word for the emotion it conveyed, from which Macy and Golder found a remarkably consistent pattern across people’s waking hours. Positive effect—language revealing that tweeters felt active, engaged, and hopeful—generally rose in the morning, plummeted in the afternoon, and climbed back up again in the early evening. Despite race, ethnicity, or culture, “the temporal affective pattern is similarly shaped” (Pink, p. 10). The same pattern was observed throughout the week, with a positive effect generally higher on weekends and starting about two hours later than on weekdays, though the overall shape stayed the same.
Working alongside other researchers, Daniel Kahneman and Alan Krueger from Princeton University created a method to chart hour-to-hour changes in how we feel: the Day Reconstruction Method (DRM). Using the DRM, participants reconstructed the previous day in 90-minute episodes, chronicling everything they did and how they felt while doing it. In 2006, Kahneman, Krueger, and crew enlisted the DRM to measure “a quality of effect that is often overlooked: its rhythmicity over the course of a day” (Daniel Kahneman et al., 2004). They asked 909 employed American women of varying races, ages, incomes, and education levels to characterize their emotions throughout the day using a list of twelve adjectives. Kahneman was also part of a second study in which women were observed to choose more positive adjectives during 12 p.m. and 8 p.m. In contrast, usage of the negative adjectives peaked at 10 a.m. and 4 p.m. One hypothesis attributed the jump in negative adjectives to the increased working environment demands and the peaking of positive adjectives at 12 p.m. to the relief provided by lunchtime. They found that women’s positive affect climbed in the morning hours until it reached an “optimal emotional point” around midday. Then, their good mood quickly plummeted and stayed low throughout the afternoon, only to rise again in the early evening.
Studies have shown that daily mood fluctuations can significantly impact business interactions. Research analyzing over 26,000 earnings calls found that calls held in the morning were more positive, while those later in the day became increasingly negative, leading to temporary stock mispricing and highlighting the importance of timing in critical decisions (Harvard Business Review, October 2013).
Clearly, our bodies operate off of some intrinsic sense of time. First discovered by Jean-Jacques d’Ortous de Marian, our internal biological clock governs a collection of circadian rhythms (from the Latin circa {around} and diem {day}) and plays a role in the proper functioning of all living things. Our "biological clock," known as the suprachiasmatic nucleus (SCN), is a cluster of about 20,000 cells located in the hypothalamus, deep within the lower center of the brain. Chronobiologists, scientists who study biological rhythms and examine physiological functions, including melatonin production, metabolic response, emotions, and behavior, have unlocked some patterns in how we feel and perform–which, in turn, helps guide our day-to-day structure.
Observing these studies shows that our cognitive performance does not remain static throughout the day; it oscillates. “Beneath the surface of our everyday life,” Pink says, “ is a hidden pattern: a peak, a trough, and a rebound.” Furthermore, our performance is context-dependent; the time that an action is being taken at matters just as much as the action itself.
The Linda problem, introduced by Daniel Kahneman and Amos Tversky in 1983, was used to illustrate the “conjunction fallacy,” one of the many ways our brains go awry based on the time of day and our chronotype. The participants were given the personality sketches of a fictitious individual called Linda, followed by a set of occupations and avocations associated with her. Linda is 31 years old, single, outspoken, and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations. Which is more likely? Linda is a bank teller, or Linda is a bank teller and is active in the feminist movement.
85% of the participants faced with this question believed that the second option was more probable than the first. As a justice-seeking antinuke philosophy major, Linda certainly seems like someone who would be an active feminist, but she “is [much] more likely to be a bank teller than she is to be a feminist bank teller, because every feminist bank teller is a bank teller, but some women bank tellers are not feminists” (Tversky and Kahneman 299). Using “set theory,” another way to explain this is that bank tellers who are feminists are a subset of all bank tellers, and subsets can never be larger than the set they are a part of.
In a 1990 study conducted by Galen V. Bodenhausen, two pools of participants comprised of undergraduate psychology students were tested with the Linda problem at different times, one at 9 a.m. and another at 8 p.m. Bodenhausen found that 29% of the participants of the 9 a.m. group did not commit the conjunction fallacy, while only 6% of the subjects of the second pool–at 8 p.m.–answered the question correctly. People were much more likely to get it right earlier in the day than later.
Ultimately, the Linda problem is an analytic task whose answer can be reached purely through logic. Humans perform best on analytic tasks when body temperature is high/near its circadian peak, alertness, energy level, and performance are at their best, enhancing our executive functioning, ability to concentrate, and ability to deduce. For most of us, our circadian peak is in the late morning or noon.
So, should we move all our most important work to the morning? Logically speaking, it sounds right to think this way, but don’t just take it at face value. Remember that what was described in the previous paragraph only applies to “analytic tasks” regarding peak performance.
Mareike Wieth and Rose Zachs showed in their 2011 study that innovation and creativity are greatest when we are not at our optimal time of day. The participants consisted of 428 university students presented with six “insight problems” and were given four minutes to complete each. One of the problems goes like this: A dealer in antique coins got an offer to buy a beautiful bronze coin. The coin had an emperor’s head on one side and the date 544 BC stamped on the other. The dealer examined the coin, but instead of buying it, he called the police. Why?
When they were tested, the participants were randomly split into two groups. One was to be tested in the morning (between 8:30 a.m. and 9:30 a.m.), and the other was to be tested in the afternoon (between 4:30 p.m. and 5:30 p.m.) The morning thinkers, whose optimal time of day was in the morning, were 37.5% more likely to figure out the coin problem in the afternoon.
Why does this occur?
Vigilance, also called “inhibitory control,” helps our brains solve analytical problems by removing distractions. That “flash of illuminance” required for insight problems is more likely to occur when there is less vigilance and fewer inhibitions. This suggests that students designing their class schedules may benefit from taking analytic subjects such as math in the morning and classes such as art and creative writing during their nonoptimal time of day.
In the mornings, when our mood peaks, most of us excel at Linda problems—analytic work that requires sharpness, vigilance, and focus. Later in the day, during our recovery, most of us do better on coin problems–insight work that requires less inhibition and resolve. Midday troughs, or the afternoon slump, are good for very little.
Each of us has a “chronotype”—a personal pattern of circadian rhythms that influences our physiology and psychology. People like Thomas Edison are late chronotypes (owls). “[Edison] was more likely to be found hard at [work] in his laboratory at midnight than midday” (McFee 148). Others of us are early chronotypes (larks). They rise easily and feel energized during the day but wear out by evening. Most of us are in between.
Roenneberg, the world’s best-known chronobiologist, offers an easy way to determine one’s chronotype. Following Roenneberg, Pink offers three characterizations of people’s chronotypes, which he labels Larks, Owls, and Third Birds. To determine which type is yours, you can think about your behavior during “free days” when you are not required to awaken at a specific time. Answer these three questions:
What time do you usually go to sleep?
What time do you usually wake up?
What is the middle of those two times (your midpoint of sleep)? (For example, if you typically fall asleep around 10:00 p.m. and wake up at 8:00 a.m., your midpoint is 3:00 a.m.
You were most likely neither a complete lark nor entirely an owl, but somewhere in the middle–what Dan Pink calls a “third bird.” “About 60 percent to 80 percent of us are third birds” (Pink 29).
In the Linda problem study, most people (the morning larks) solved Linda problems more readily at 8 a.m. than at 8 p.m. However, some people (the nighttime owls) showed the reverse tendency. They were more likely to avoid the conjunction fallacy and produce the correct answer at 8 p.m. rather than at 8 a.m.
The same goes for the insight problems. Larks and third birds had their flashes of illuminance later in the day, during their less optimal recovery stage when their inhibitions had fallen. However, owls spotted the fraud more readily in the early mornings, their less optimal time.
“The synchrony effect” is the superior performance of a particular task at optimal times of the day or inferior performance of a particular task at suboptimal parts of the day. For example, although it is more dangerous for larks and third birds to drive at night, owls actually drive worse early in the day because mornings are out of sync with their natural cycle of vigilance and alertness. Synchrony also affects our ethical behavior. A 2014 study showed that people with early chronotypes were less likely to lie and cheat on tasks in the morning than later in the day, whereas night owls are more ethical at night than in the morning.
All of us experience the day in three stages—a peak, a trough, and a rebound. And about three-quarters of us (larks and third birds) experience it in that order. But about one in four people, night owls, experience the day in something closer to the reverse order—recovery, trough, peak. Chronotype is important because it influences job behavior and performance, as statistics show.
Around 20 to 25 percent of the population are strong evening types. The problem is that our corporate, government, and education cultures are configured for the 75 or 80 percent of people who are larks or third birds. Owls are like left-handers in a right-handed world—forced to use scissors and writing desks and catcher mitts designed for others. How they respond is the final piece of the puzzle in divining the rhythms of the day.
So, how can you adjust your schedule to fit your chronotype? First, understand your task, and then select the appropriate time. Is your own hidden daily pattern peak-trough-rebound? Or is it rebound-trough-peak? Then, look for synchrony. Try to nudge your most important work, which usually requires vigilance and clear thinking, into the peak and push your second-most important work, or tasks that benefit from disinhibition, into the rebound period.
If you're a boss, understand these two patterns and allow people to work at their peak. For example, Till Roenneberg conducted experiments at a German auto plant in a steel factory in which he rearranged work schedules to match people's chronotypes to their work schedules. The results were greater productivity, reduced stress, and higher job satisfaction.
If you have a free hour in the morning and are a lark or a third bird, don’t waste your time. Instead, you should productively spend that hour doing the work that you find is most important.
No matter what your chronotype is, you will be happier and more productive if you work with it, rather than against it.
Citations:
Scott A. Golder and Michael W. Macy, “Diurnal and Seasonal Mood Vary with Work, Sleep,
and Daylength Across Diverse Cultures,” Science 333, no. 6051 (2011): 1878-81
Daniel Kahneman et al., “A Survey Method for Characterizing Daily Life Experience: The
Day Reconstruction Method,” Science 306, no. 5702 (2004):1776–80
Arthur A. Stone et al., “A Population Approach to the Study of Emotion: Diurnal Rhythms
of a Working Day Examined with the Day Reconstruction Method,” Emotion 6, no. 1
(2006): 139-49
Jing Chen, Baruch Lev, and Elizabeth Demers, “The Dangers of Late-Afternoon Earnings
Calls,” Harvard Business Review, October 2013
Russell G. Foster and Leon Kreitzman, Rhythms of Life: The Biological Clocks That Control the
Daily Lives of Every Living Thing (New Haven, CT: Yale University Press, 2005), 11.
Silver, Rae, and William J Schwartz. “The suprachiasmatic nucleus is a functionally
heterogeneous timekeeping organ.” Methods in enzymology vol. 393 (2005): 451-65.
doi:10.1016/S0076-6879(05)93022-X
Amos Tversky and Daniel Kahneman, “Extensional Versus Intuitive Reasoning: The
Conjunction Fallacy in Probability Judgment,” Psychological Review 90, no. 4 (1983): 293–
315
Galen V. Bodenhausen, “Stereotypes as Judgmental Heuristics: Evidence of Circadian
Variations in Discrimination,” Psychological Science 1, no. 5 (1990): 319–22
Folkard, Simon. "Diurnal Variation in Logical Reasoning." British Journal of Psychology, vol.
66, 1975, pp. 1-8. doi:10.1111/j.2044-8295.1975.tb01433.x.
Wright, Kenneth P., Jr., Joseph T. Hull, and Charles A. Czeisler. "Relationship Between
Alertness, Performance, and Body Temperature in Humans." American Journal of
Physiology-Regulatory, Integrative and Comparative Physiology, vol. 283, no. 5, 2002, pp.
R1370-R1377. doi:10.1152/ajpregu.00205.2002.
Mareike B. Width and Rose T. Zacks, “Time of Day Effects on Problem Solving: When the
Non-optimal Is Optimal,” Thinking & reasoning 17, no. 4 (2011): 387-401.
Lynn Hasher, Rose T. Zacks, and Cynthia P. May, “Inhibitory Control, Circadian Arousal,
and Age,” in Daniel Gopher and Asher Koriat, eds., Attention and Performance XVII:
Cognitive Regulation of Performance: Interaction of Theory and Application (Cambridge,
MA: MIT Press, 1999), 653-75
Inez Nellie Canfield McFee, The story of Thomas A. Edison (New York: Barse & Hopkins, 1922)
Till Roenneberg et al., “Epidemiology og the Human Circadian Clock,” Sleep Medicine
Reviews 11, no. 6 (2007): 429-38
Pink, Daniel H. When: The Scientific Secrets of Perfect Timing. Riverhead Books, 2018
Cynthia P. May and Lynn Hasher, “Synchrony Effects in Inhibitory Control over Thought
and Action,” Journal of Experimental Psychology: Human Perception and Performance 24,
no. 2 (1998): 363–79
Correa, Angel et al. “Effects of chronotype and time of day on the vigilance decrement
during simulated driving.” Accident; analysis and prevention vol. 67 (2014): 113-8.
doi:10.1016/j.aap.2014.02.020
Pack AI, Pack AM, Cucchiara A, et al. "Characteristics of Crashes Attributed to the Driver
Having Fallen Asleep." Accident Analysis & Prevention, vol. 27, no. 6, 1995, pp. 769–775.
Pergamon Press,
Jim Horne and Louise Reyner, “Vehicle Accidents Related to Sleep: A review,” Occupational
and Environmental Medicine 56, no 5 (1999) 289-94
Anderson, John A E et al. “Timing is everything: Age differences in the cognitive control
network are modulated by time of day.” Psychology and aging vol. 29,3 (2014): 648-657.
doi:10.1037/a0037243
Vetter, Céline et al. “Aligning work and circadian time in shift workers improves sleep and
reduces circadian disruption.” Current biology: CB vol. 25,7 (2015): 907-11.
doi:10.1016/j.cub.2015.01.064
Debono, Miguel et al. “Modified-release hydrocortisone to provide circadian cortisol
profiles.” The Journal of clinical endocrinology and metabolism vol. 94,5 (2009): 1548-
54. doi:10.1210/jc.2008-2380
llinois State Board of Education. Recess: Is It Needed? Illinois State Board of Education,
2004. Illinois State Board of Education,
Francesca Gino, “Don’t make Important Decisions Late in the Day,” Harvard Business Review,
February 23, 2016
Ariga, Atsunori, and Alejandro Lleras. “Brief and rare mental "breaks" keep you focused:
deactivation and reactivation of task goals preempt vigilance decrements.” Cognition
vol. 118,3 (2011): 439-43. doi:10.1016/j.cognition.2010.12.007
Emily M. Hunter and Cindy Wu, “Give Me a Better Break: Choosing Workday Break
Activities to Maximize Resource Recovery.” Journal of Applied Psychology 101, no. 2
(2016): 302-11
Gifford, Julia. “52/17 Updated – People Are Now Working and Breaking Longer than before
| DeskTime Blog.” Desktime.com, 10 Aug. 2021, desktime.com/blog/52-17-updated-
Audrey Bergouignan et al., “Effect of Frequent Interruptions of Prolonged Sitting on Self-
percieved levels of Energy, Mood, Food Cravings, and Cognitive
Function,” International Journal of Behavioral Nutrition and Physical Activity 13, no. 1
(2016): 13-24
Sooyeol Kim, Young Ah Park, and Qikun Niu, “Micro-Break Activities at Work to recoever
from Daily Work Demands,” Journal of Organizational Behavior 38, no. 1 (2016): 28-41
Kristen M. Finkbeiner, Paul N. Russel, and William S. Helton, “Rest Improves Performance,
Nature Improves Happiness: Assessment of Break Periods on the Abbreviated
Vigilance Task,” Consciousness and Cognition 42 (2016): 277-85
Marjaana Sianoja et al., “Recovery During Lunch Breaks: Testing Long-Term Relations with
Energy Levels at Work,” Scandinavian Journal of Work and Organizational Psychology 1,
no. 1 (2016):1-12
Honjai Rhee and Sudong Kim, “Effects of Breaks on Regaining Vitality at Work: An
Empirical Comparison of ‘Conventional’ and ‘Smartphone’ Breaks,” Computers in
Human Behavior 57 (2016): 160-67
Mark R. Rosekind et al., “Crew Factors in Flight Operations 9: Effects of Planned Cockpit
Rest on Crew Performance and alertness in Long Haul Operations,” Nasa Technical
Reports Server, 1994, available at https://ntrs.nasa.gov/search.jsp?R=19950006379
Tracey Leigh Signal et al., “Scheduled Napping as a Countermeasure to Sleepiness in Air
Traffic Controllers,” Journal of Sleep Research 18, no. 1 (2009): 11-19.
Garbarino, Sergio et al. “Professional shift-work drivers who adopt prophylactic naps can
reduce the risk of car accidents during night work.” Sleep vol. 27,7 (2004): 1295-302.
doi:10.1093/sleep/27.7.1295
Beijamini, Felipe et al. “After being challenged by a video game problem, sleep increases the
chance to solve it.” PloS one vol. 9,1 e84342. 8 Jan. 2014,
doi:10.1371/journal.pone.0084342
Comments