Consider this puzzle: An antiquities dealer is deciding whether to purchase a coin. The coin is made of bronze, with an emperor’s head engraved on one side and the date 544 B.C. stamped on the other. The dealer quickly determines the coin is fake. How? Whether (or how quickly) you come up with the right solution might very well depend on the time of day you’re reading this, says Cynthia May, PhD, a professor of psychology at the College of Charleston in South Carolina.
The answer: Coins were never stamped “B.C.,” because the designation didn’t exist at the time. In solving the riddle, people are often carried away by their logic, May explains. “They’re thinking, ‘When was bronze first used?’ and ‘Were there emperors during that period?’ when in fact they have to let go of their first interpretation to solve the problem.” Turns out, the best time of day to solve such “insight” problems, or to undertake a creative challenge, is not the same time of day you’d want to take a math test or solve a problem that requires careful analysis. Researchers are turning up all kinds of evidence that one’s cognitive performance fluctuates in predictable patterns throughout a day. “The time at which you do things matters,” May says.
Researchers from a variety of fields have noted some of the ways that timing makes a difference, in matters from medicine to business. Madhusudhan Sanaka, MD, at the Cleveland Clinic, and colleagues studied colonoscopy data from more than 3,600 people and found that physicians identified significantly more abnormalities during morning colonoscopies than during those performed in the afternoon (The American Journal of Gastroenterology, Vol. 104, No. 7, 2009).
Moods, too, rise and fall predictably during the day. Scott Golder, PhD, and Michael Macy, PhD, at Cornell University, studied language from millions of public Twitter posts from around the globe. They found the average Twitter user had a happiness spike around breakfast, hit a grumpy slump in the late afternoon and perked up again after dinner (Science, Vol. 333, No. 6051, 2011). “We found an incredibly robust pattern, across diverse cultures all over the world,” Macy says. The time-sensitive nature of moods can have surprising ripple effects as well. Jing Chen, PhD, at the University of Buffalo School of Management, and colleagues analysed quarterly earnings conference calls and found that financial executives and analysts were upbeat in the morning and became more negative as the day wore on. Those mood changes led the analysts to make more errors related to stock pricing in the afternoon (Management Science, online first publication, 2018). Given these findings, should you schedule important tasks for the morning and give afternoons over to an extended siesta? It’s not that simple, other research finds. People’s cognitive abilities fluctuate throughout the day by their circadian patterns or chronotypes.
We all fall into one of five different chronotypes, defined by the window of time we feel most alert and energetic, May explains: strong morning types, moderate morning types, strong evening types, moderate evening types and those who are neutral, who peak midday. Whether you bounce out of bed before sunrise with the larks, prefer the company of owls and bats or hover somewhere in between, most people know intuitively which category they belong to. If you’re not sure, a systematic assessment can help you figure it out. Researchers use several surveys to measure chronotype, including the Morningness-Eveningness Questionnaire (MEQ), the Composite Scale of Morningness (CSM) and the Munich Chronotype Questionnaire (MCTQ). Our daily patterns are more than mere preferences, though, says Dorothee Fischer, PhD, a research fellow at Harvard Medical School/Brigham and Women’s Hospital who studies circadian rhythms. “Chronotype isn’t a personality trait, but a biological characteristic,” she says. Our sleep-wake cycles are governed by a small but powerful master clock known as the suprachiasmatic nucleus (SCN), a cluster of neurons located within the hypothalamus. The SCN does its job with input from environmental factors—most notably, light exposure. Yet sunshine is only part of the story. Our underlying rhythms are rooted in our genes. Lark and owl tendencies often run in families. That doesn’t mean chronotypes are fixed, however. “As we age, our circadian rhythmicity shifts,” says May. On the whole, young children are more often morning types, but by their teens and early 20s a majority have shifted to favouring evenings, or to being neutral, leaning toward evening. In older age, we slide back toward favouring the morning hours. Yet there’s considerable variation among individuals—and that variation translates to differences in our peak times for maximum brainpower.
Time to focus
Cognitively speaking, morning people are generally at their best during the morning, while evening people perform better in the afternoon. “You are way better off doing difficult mental chores at a time consistent with your chronotype,” says Lynn Hasher, PhD, a professor of psychology at the University of Toronto who studies circadian patterns and attentional processes. Research has shown that these so-called synchrony effects hold for people of all ages, from adolescents to older adults. In one example, Hasher and colleagues presented a suite of executive function tasks to adolescents who identified either as morning types or evening types. The participants took the tests either in the morning or the afternoon. Lark or owl, students, tested during their peak times scored higher on working memory, decision-making and overall executive functioning than students tested at off-peak times (Developmental Science, Vol. 15, No. 3, 2012).
In another study, Hasher, May and colleagues tested older and younger adults at their peak and nonpeak times. The tests evaluated implicit memory (automatic, almost unconscious recall of well-known information) as well as explicit memory (the conscious, deliberate effort to process and retrieve information). In both groups, participants had better explicit memory during their peak times of the day. For implicit memory, however, the results were flipped: Morning types had better implicit memory in the afternoon, while evening types scored higher in the morning (Psychological Science, Vol. 16, No. 2, 2005). Those results make sense when you think of daily peaks regarding distractions, May explains. Inhibition is an important part of an executive function, allowing us to focus on important tasks by filtering out the unimportant details. During off-peak times of day, inhibition wavers and we have a harder time tuning out that irrelevant information. That’s why tasks that require focus and analytic thought are best tackled at peak times. Creative endeavours, on the other hand, might best be undertaken at off-peak times. Psychologists Mareike Wieth, PhD, and Rose Zacks, PhD, found that people were better able to solve problems requiring a flash of creative insight—such as the bronze coin puzzle—during their off-peak times of day (Thinking & Reasoning, Vol. 17, No. 4, 2011). “If you’re doing a task where you want to entertain lots of different possibilities and think outside the box, then operating at your nonoptimal time is to your advantage,” May says.
What if you identify as a neutral type, without a strong preference for early mornings or late nights? Unfortunately, little is known about timing effects for this group. Most studies of chronotype and performance so far have focused on people with strong morning or evening tendencies. However, researchers are beginning to explore the neutral territory. Hasher and May gave a battery of cognitive tests to two groups of neutral-type adults, ages 17 to 21 and ages 70 to 74. The older adults performed best at midday, with notable timing effects for inhibition, executive function, long-term memory and forgetting. The younger adults, on the other hand, showed no differences in performance when tested in the early morning, midday or evening (Timing & Time Perception, Vol. 5, No. 2, 2017).
Meanwhile, other research suggests that timing effects become more important with age. Hasher and her colleagues compared cognitive control between morning-type elderly adults and young adults who trended toward evening type. The participants completed a series of tasks to measure attention and distraction while inside a fMRI scanner. When older adults were tested in the morning, at their peak time, they were more likely to ignore distracting information, performing more similarly to young adults tested in the afternoons. When tested at their peak time, the older participants showed activation in the same brain regions as their younger counterparts. But when tested at nonoptimal times, older adults were more easily distracted and recruited different neural networks to do the work (Psychology and Aging, Vol. 29, No. 3, 2014).
Time-of-day effects have wide-ranging implications. A large body of research has highlighted the fact that early school start times may be detrimental to adolescents and young adults, who are more likely to perform at their peak in the afternoon and evening. In light of such research, some school districts have started shifting high school start times later. But many high schools and college classes still begin bright and early, and tests such as the SAT are often scheduled during the morning hours. For students counting on those test results to get into college, timing effects are hardly trivial. In one study, Hasher and colleagues gave intelligence tests to 11- to 14-year-olds, testing both morning and evening types at optimal and nonoptimal times of the day. IQ estimates were an average of 6 points lower when children were tested at their non-peak rather than their peak times (Personality and Individual Differences, Vol. 42, No. 3, 2007).
Employers might also consider the effects of timing on workers’ well-being. Fischer and colleagues conducted an experiment in which they matched shift workers’ schedules to their chronotypes. “The earliest group of chronotypes didn’t work the night shift, and the latter group didn’t work the morning shift. By this simple tweak, we could improve sleep duration, circadian disruption and well-being,” Fischer says (Current Biology, Vol. 25, No. 7, 2015). Researchers, too, might want to think about how the timing of their experiments might skew results. “Researchers across disciplines need to consider the time at which they are testing their participants,” May says.
The same is true for psychologists in clinical practice, she says. If you’re using neuropsychological tests to diagnose or monitor conditions such as dementia or autism, testing times could influence the findings. Imagine testing an older adult for cognitive decline in the morning, then following up months later with a test in the afternoon. The timing differences might lead you to conclude that the decline is progressing more rapidly than it is. Timing might even make certain psychotherapy techniques more or less effective, May says. “If you give your clients homework, it can be important to consider when to have them execute it.” The MEQ is quick and easy to administer, she says, and the results can help guide a psychotherapist’s recommendations for clients.
Regardless of chronotype or profession, most people can find small ways to tweak their daily schedules for maximum benefit. If you’re a morning person, for instance, resist the temptation to go through your emails first thing in the morning and try diving into your deep work right away. “You should save the mundane administrative stuff until the afternoon and spend the morning on more difficult tasks like writing manuscripts, analysing data or planning experiments,” May says. The principle extends outside the office, too. If you’re meeting with a financial planner to discuss complicated investment options, schedule the appointment at a time when you’re at your cognitive peak. If you’re trying to interpret some puzzling research data, revisit it during your off-peak coffee break.
Unfortunately, typical 9-to-5 work schedules can make it hard for night owls to match their chronotype to the world’s rhythms, a disconnect known as “social jet lag.” But there are ways to shift your rhythm, at least a little, says Fischer. Being exposed to bright lights at night can push circadian patterns later into the evening. That’s especially true of the blue light common in electronic devices. But lights are easy to adjust. “Reducing evening light exposure has an advancing effect on your circadian clock,” Fischer says. By dimming lights when it gets dark outside and using the light-filtering software on their devices, evening types can shift their biology to a (slightly) earlier rhythm. Still, it’s probably impossible to transform an extreme night owl into a lark, Fischer adds. So, respect your circadian rhythms and try to schedule your days accordingly. “People sometimes underestimate the biological component of chronotypes,” she says. “It’s hard to work against your biology.”
Credit: Kirsten Weir for Monitor On Psychology, June 2018.