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It's well known that we follow circadian, or daily, rhythms in basic physiological functions like body temperature or digestion. Interestingly, these rhythms extend to our psychological abilities, too. Simply put, we tend to have more brainpower at our peak circadian arousal time, which leads to success on activities that require us to concentrate and mentally buckle down.

Morning types (people who are most alert in the morning) excel on a host of cognitive tasks when they complete them early in the day. This is especially true for tasks that require working memory, like systematically reasoning through a problem or juggling numbers in your head. As I have blogged about before, working memory is our flexible mental scratch pad. It's the brainpower that helps us keep what we want in mind and what we don't want out. On the other hand, evening types, those who are most alert at night, tend to perform at their best on demanding cognitive tasks later in the day.

But not all tasks require working memory for success. In fact, sometimes people's ability to think about information in new and unusual ways can actually be hampered when they wield too much brainpower. This means that what we think of as our optimal time of day may not be optimal for everything.

Recent research confirms this idea. In a paper published last December in the journal Thinking and Reasoning, psychologist Mareike Wieth and her colleagues found that when people have to solve "insight problems" that require a high degree of creativity, solvers are much more successful when they tackle these problems at the time of day in which they are least alert.

Take the following problem:

Water lilies double in area every 24 hours. At the beginning of summer there is one water lily on the lake. It takes 60 days for the lake to become completely covered with water lilies. On which day is the lake half covered?

This water lilies puzzle is called an "insight problem" because the solver feels that the answer comes all at once, in an "Aha!" moment of illumination (the answer, by the way, is day 59). This is compared to more analytic problems that require the solver to grind out the solution by systematically working towards the answer, incrementally narrowing down the problem search space—which requires a heavy dose of working memory.

What Wieth and her colleagues did was ask volunteers to fill out a questionnaire that assessed whether they were at their best in the morning or evening (this questionnaire, by the way, is highly predictive of people's peak circadian arousal). She then invited the volunteers to the lab to solve both insight and analytic problems in either the morning (between 8:30 and 9:30 AM) or the afternoon (between 4:30 and 5:30 PM). While people did slightly better on the analytic problems during their optimal time of day, volunteers were much more likely to come up with a creative—and correct—answer to the insight problems at their self-professed non-optimal time.

We often assume that when our circadian arousal is at its peak, we will perform better at whatever we put our minds to. That's why morning people carve out times to work in the AM and evening people tend to burn the midnight oil. Now we know that certain activities benefit from us NOT being in our most alert state. Simply put, when you have to be creative, working at your non-optimal time of day is actually optimal.

For more on performing at your best, check out my book "Choke"

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Mareike B. Wieth & Rose T. Zacks (2011): Time of day effects on problem solving: When the non-optimal is optimal, Thinking & Reasoning, 17, 387-401

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