Morning ‘larks’ tend to be more error-prone during late evening hours than night ‘owls,’ study finds

Burning the midnight oil — specifically, staying up for 18 hours and then trying to tackle a task that requires the mind to be attentive — is much more problematic for morning people than for night people, according to a small British study published recently in the journal Experimental Brain Research.

Morning “larks” tend to finish such late night tasks more quickly than night “owls,” but they also tend to make more mistakes because of a dip in their ability to control and focus their attention, the study found.

This study is interesting to anyone who wonders how their day-to-day activities are affected by their chronotype (the overall daily timing of the body’s sleep/wake cycle, which is connected to host of other biological functions, including peaks in mental alertness). But the study’s findings may have particular implications for people whose jobs require vigilant attention and alertness in the late evening hours, such as pilots, emergency medical personnel and truck drivers.

Study details

It’s long been known that morning people (those with an early-to-rise-early-to-bed chronotype) work less efficiently at night than evening people (those whose chronotype leaves them struggling to put two sentences together at the breakfast table, but enables them to be wide-eyed for many hours after dinner). Scientists have been unsure, however, about which cognitive factors explain this difference.

With that knowledge gap in mind, the authors of this new study decided to investigate how a specific cognitive process — attention — differs between morning and evening people after a sustained period of wakefulness.

The researchers — cognitive psychologists Nicola Barclay of the University of Oxford and Andriy Myachykov of the Center for Cognition and Decision Making at Higher School of Economics in Moscow, recruited 26 volunteers, 13 men and 13 women. Their ages ranged from 18 to 40, with an average age of 25. All were healthy (free of any major health issues) and self-reported that they had no sleep issues.

The volunteers were instructed to stay awake for 18 hours, from 8 a.m. to 2 a.m., and to follow their normal routine during those hours. At the start and again at the end of this period of wakefulness, the participants were asked to complete two assessments. One, the Attention Network Test (ANT), evaluated their ability to solve unusual attention-related tasks. The other, the Morningness-Eveningness Questionnaire, helped to determine where they fell on the morning-evening chronotype continuum.

The results of these assessments revealed no important differences between early birds and night owls when they took the 8 a.m. test. But two major — and somewhat surprising — differences were found between the groups’ scores when the test was retaken at 2 a.m.

“Contrary to expectation we found that morning types were faster overall in a global measure of attention at 2 a.m. than evening types,” said Barclay in an interview with MedicalResearch.com. “However, morning types were more likely to make errors than evening types.”

More specifically, said Barclay, “we found that evening types outperformed morning types on measures of executive control, which require the individual to inhibit or ignore conflicting information. This type of attentional process requires more cognitive effort and conscious control than other types of attention, which are more automatic.”

In other words, the night owls were more likely to sacrifice speed for accuracy.

Why? Perhaps, say Barclay and Myachykov in their paper, because evening people take a more earnest approach to tasks that require their attention during their preferred period of the day — the evening and night. 

It’s also possible that “the slower speed of response by evening types is due to an accumulation of sleep debt over the working week,” said Barclay. “We know that evening types are particularly vulnerable to ‘social jetlag,’ which manifests as symptoms akin to jetlag. Social jetlag refers to the misalignment between the biological clock and time constraints imposed by social commitments. Evening types may be forced to awaken earlier in the morning to attend work, earlier than their biological clock would ordinarily dictate. Yet evening types often maintain a late bed time in line with the biological clock. Thus, the sleep duration of evening types is often very short, resulting in a sleep debt which then accumulate over the working week.”

Limitations and indications

Of course, this study comes with major caveats. Most notably, it involved a very small number of participants, and the experiment was conducted only once, after a single day of sustained wakefulness.

“These results should be considered preliminary,” write Barclay and Myachykov, “and future studies should address these questions with larger samples.”

Still, the results are interesting and, as the two researchers point out, “contribute to a better understanding of the effects of sleep deprivation, chronotype, and time-of-day effects on cognitive functioning.” 

“Our results highlight that morning-types may be particularly vulnerable to failures in executive control in the later evening,” they conclude, “which may have direct implications on risk of accidents particularly on tasks requiring inhibitory control.”

FMI: The study can be read in full at the Experimental Brain Research website.