How Circadian Rhythms and Sleep Patterns Affect Learning and Performance
Circadian rhythms, or each person’s internal “body clock” that clicks through the day setting off urges to sleep, eat, and complete other daily actions, have a larger affect on our lives than one might realize. Every body has a definitive time of day in which it is most alert, least alert, most active and most tired, and screwing with this natural cycle can be disastrous. Shift work forces most people to work outside their natural, circadian determined working hours, like working nights or evenings, so that not only do workers find it more difficult to concentrate on their job while they are doing it, they also have more trouble relaxing and falling asleep during their off-hours. Your circadian biological clock can be “reset” over time using light therapy and gradually shifting sleep times to the desired pattern, but many shift workers try to sleep normal hours during their days off and opposite hours when they work night shifts, further disrupting their body clock. Several methods can help night workers and extended hours workers determine the workings of their own circadian rhythms and biological clock, and to better adapt themselves to shift work schedules.
Circadian Rhythms
Daily variations in behavior and the body functions, occurring on a roughly 24-hour cycle is known as the circadian rhythms. Circadian rhythms influence physiological functioning in human beings. Examples include rhythms in the core body temperature, blood sugar, sleep-wake cycle, heart rate and hormonal circulation. Circadian rhythms can impact the ability of tissues to absorb drugs and can lead to variations of symptoms impacting disease severity. The evidence from the studies cited above indicates that reduced regulation of attention is impacted by circadian cycles.
We are all familiar with the saying “early to bed, early to rise, makes a man healthy,wealthy, and wise”. From this we would conclude that it is best for all of us to be morning people. But, is this really true?
Chronotypes
People can be divided into different chronotypes: Morning people, intermediate people and evening people, according to the shape of their circadian rhythms. The chronotype of a person can be determined using a simple test developed by Horne and Ostberg (1976, 1977) called the Morningness-Eveningness Questionnaire (MEQ). The test includes such questions as “If you went to bed at 11 pm, at what level of tiredness would you be?” The test puts people into five categories, ranging from “definitely morning” to “definitely evening”. The questionnaire has been proven to have good reliability in terms of correlation to other attributes such as variation in body temperature, sleep-wake cycles and periods of perceived alertness (Tankova, Adan & Buela-Casal, 1994). Find out what chronotype you are by taking the Morningness-Eveningness quiz at the end of this paper.
While there are people of all chronotypes in all age groups, there are shifts in preferences as people get older. A review of literature indicates the following preferences for the age groups noted:
Children and Adolescents: Younger children’s time of day preference is more towards morning and older children’s preference is more towards evening. Kim et al. (2002) studied 900 US children ranging in age from 8 to 16. The shift of preference from morning to evening occurs around the age of 13. Kim et al. found variability in each age group.
Younger Adults: May et al. (1993) also studied 210 university undergraduates between the ages of 19 and 22. Only 6% were found to be morning types; 94% were found to be either “definitely evening” or “moderately evening” types. None were “definitely morning” types.
Older Adults: Very few older adults are evening types (less than 2%). May et al. (1993 study) examined 91 older adults between the ages of 66 and 78. Nearly 75% of the older adults tested were either definite or moderate morning types.
Implications to Performance
The varying time of day preferences by age has been proven to have an impact on cognitive functioning and performance. Comparing older to younger adults, it is clear that younger adult test scores, focusing of cognitive functioning, improve from the morning testing times to the afternoon times while those of older adults decline (Hasher, Goldstein and May, It’s About Time; Circadian Rhythms, Memory and Aging).
In addition, the data resulting from the study suggests that performance is better when it is assessed at an optimal time rather than at a non-optimal time. Called “the synchrony effect” by Hasher (1998), there is a benefit to matching task demands with preferred time of day.
The Synchrony Effect
The first set of studies attempted to document declines in performance from optimal tonon-optimal times of day. One test focused on people’s ability to resist distraction during a verbal problem-solving task. Each problem incorporates three words, which can only be related to each other by generating a fourth word. The participant’s task was to determine the fourth word. For example, the following three words can be associated to each other by the word sick: sea, home and stomach. The three words were either presented alone or with some distracting words that were clearly different from the target words. The distraction could either be helpful or harmful (misleading). Participants were instructed to ignore the distracting words.
Performance on this basic problem-solving task without any distraction did not vary with age or time of testing. All participants got about a third of the problems right. Young adults were bothered by the distractions in the morning but not late in the afternoon. For older adults, the distraction was more harmful in the afternoon.
Other studies have supported the results of this test; all show poorer performance at nonoptimal times of day. Yoon et al. 1999, measures immediate memory using a classic digit span task, one that starts with a short series of numbers and asks for serial order recall, going to an increasingly longer series of numbers. Young and old adults do not differ in the morning, but younger adults improved their span across the day while older adults reduced their span. In another study (reported in Winocur & Hasher, 2002, based on unpublished data by May), participants read two brief stories and then recall them immediately and twenty minutes later. Based on recalling the essence of facts in the original stories, the scoring indicated that young and older adults remember and forget about the same amount of facts in the morning. But, there is a substantial decline in performance by older adults during the day; they forgot just five facts in the morning and about 14 in the afternoon, nearly tripling the size of the forgetting effect.
In another study by May & Hasher, a list of words was presented for participants to rate for pleasantness. Then participants were given the first three letters of words on the initial list as cues to help them remember words on that list. Again, there were minimal differences between younger and older adults in the morning but substantial differences in the afternoon with young adults improving in the afternoon and older adults declining.
One study indicates that at non-optimal times, people are more likely to use easily accessible stereotypes to judge individuals than at optimal times (Bodenhausen, 1990). In a related test, people are asked to occasionally withhold a response they would otherwise make most of the time. Young adults made more errors in the morning than in the
afternoon and older adults made more errors in the afternoon (May & Hasher, 1998).
Conclusion
People have less control over attentional processes at non-optimal times. Their ability to ignore distractions and evaluate responses for appropriateness is reduced at non-optimal times of day. At non-optimal times, people are more likely to have difficulty remembering and are more likely to use simple and more easily accessible decision and retrieval paths versus more difficult ones that involve analysis and evaluation. Strong responses in both thought and action are more likely to exist at non-optimal versus optimal times of day.
The studies cited in this paper result in a strong implication that circadian rhythms have a direct impact on learning and performance.
Morningness-Eveningness Scale
Read each question carefully. Select the most appropriate answer and note the corresponding value next to it.
1. If you were entirely free to plan your evening and had no commitments the next day, at what time would you choose to go to bed?
1. 2000hrs – 2100hrs….. 5
2. 2100hrs – 2215hrs….. 4
3. 2215hrs – 0030hrs….. 3
4. 0030hrs – 0145hrs….. 2
5. 0145hrs – 0300hrs….. 1
2. You have to do 2 hours physically hard work. If you were entirely free to plan your day, in which of the following periods would you choose to do the work?
1. 0800hrs – 1000hrs….. 4
2. 1100hrs – 1300hrs….. 3
3. 1500hrs – 1700hrs….. 2
4. 1900hrs – 2100hrs….. 1
3. For some reason you have gone to bed several hours later than normal, but there is no need to get up at a particular time the next morning. Which of the following is most likely to occur?
1. Will wake up at the usual time and not fall asleep again…….4
2. Will wake up at the usual time and doze thereafter…………….3
3. Will wake up at the usual time but will fall asleep again…….2
4. Will not wake up until later than usual……………………………..1
4. You have a 2 hour test to sit which you know will be mentally exhausting. If you were entirely free to choose, in which of the following periods would you choose to sit the test?
1. 0800hrs – 1000hrs…..4
2. 1100hrs – 1300hrs…..3
3. 1500hrs – 1700hrs…..2
4. 1900hrs – 2100hrs…..1
5. If you had no commitments the next day and were entirely free to plan your own day, what time would you get up?
1. 0500hrs – 0630hrs…..5
2. 0630hrs – 0745hrs…..4
3. 0745hrs – 0945hrs…..3
4. 0945hrs – 1100hrs…..2
5. 1100hrs – 1200hrs…..1
6. A friend has asked you to join him twice a week for a workout in the gym. The best time for him is between 10pm – 11pm. Bearing nothing else in mind other than how you normally feel in the evening, how do you think you would perform?
1. Very well…………. . .1
2. Reasonably well.….2
3. Poorly…………….. ….3
4. Very poorly…….. …..4
7. One hears about ‘morning’ and ‘evening’ types of people. Which of these types do you consider yourself to be ?
1. Definitely morning type……… ……………..6
2. More a morning than an evening type……4
3. More an evening than a morning type……2
4. Definitely an evening type…. ……………… 0
Now add the scores together to get your total and compare your total score with the table below:
Morningness – Eveningness Scale
1. Definitely morning type ………..32 – 28
2. Moderately morning type ………27 – 23
3. Neither type …………………………22 – 16
4. Moderately evening type………. 15 – 11
5. Definitely evening type…………..10 – 6
(Adapted from an article: A Self Assessment Questionnaire to Determine Morningness-Eveningness in Human Circadian Rhythms. by J.A. Horne and O. Ostberg, International Journal of Chronobiology, 1976, Vol. 4, 97- 110).
©2006workingnights
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Tags: alertness, biological clock, circadian rhythms, sleep, training, Working Nights
