Perhaps you are the kind of person who likes to sleep late and stay up late, saving your important schoolwork for late afternoon or evening, when you are feeling at your peak. Or perhaps you are more of a morning person, regularly getting up early without the aid of an alarm clock. Moreover , perhaps you tend to do all your important work early in the day , when you are feeling at your best, and get to sleep fairly early in the evening. Being a morning type or an evening type of person appears to be a stable characteristic. Personality psychologists have become interested in such stable differences between persons in preferences for dif ferent times of the day and have coined the term morningness-eveningness to refer to this dimension (Horne & Ostberg, 1976).
Differences between morning and evening types of persons, sometimes called "larks" and "owls," appear to be due to dif ferences in underlying biological rhythms. Many biological processes have been found to fluctuate around an approximate 24 to 25-hour cycle. These have been called circadian rhythms (circa means "around," dia means "day," or "24 hours"). Of particular interest have been circadian rhythms in body temperature and endocrine secretion rates. For example, on average, body temperature shows a peak around mid-evening (between 8 and 9 p.m.) and a trough in the early morning (around 6 a.m.). Figure 7.5 presents a graph of body temperature by time of day .
Researchers use a temporal-isolation design to study such circadian rhythms. In this design, participants volunteer to live in an environment totally controlled by the experimenter with respect to time cues. There are no windows, so the participants do not know if it is day or night. There are no regularly scheduled meals, so the participants do not know if it is breakfast-, lunch-, or suppertime. Participants are given food whenever they ask for it. There is no access to live television or radio. Instead, the participants have a lar ge collection of videotapes and audiotapes for entertainment. Volunteers live in this environment for several weeks or longer. Often, the participants are students who want to use the time in
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Circadian rhythm in body temperature.
isolation as an opportunity to study for an important exam or who need to write a Ph.D. thesis.
Imagine being a participant in such a study . You would go to sleep whenever you wanted, sleep as long as you wanted, eat whenever you felt like it, work or watch movies as the inclination struck, and so on. This is called free running in time, in which there are no time cues to influence your behavior or biolog . If you were in such a situation and your temperature were taken every hour , and if you were like the average person, you would find that your temperature followed an approximate 24 to 25-hour cycle, starting to rise before waking up and falling before going to sleep (Aschoff, 1965; Finger, 1982; Wever, 1979).
Note that 24- to 25-hour rhythms are the average; there are wide dif ferences between persons in the actual length of their biological rhythms (Kerkhof, 1985). Circadian rhythms in temporal-isolation studies have been found to be as short as 16 hours in one person and as long as 50 hours in another person (W ehr & Goodwin, 1981). While free running in a temporal-isolation experiment, the first person woul complete a sleep-wake cycle every 16 hours, whereas the second person' s sleep-wake cycle would last 50 hours.
Such wide differences between persons are only evident in a temporal isolation situation. In real life, there are time cues all around us that fluctuate in a 24-hou rhythm—most notably, the light-dark cycle. These cues entrain us and make us fit int the 24-hour day . Even though people with short and long biological cycles entrain quite well to the 24-hour cycle, there nevertheless are dif ferences between those people in terms of the timing of peaks and valleys in their biological rhythms. Imagine someone with a slightly long circadian rhythm (such as 26 hours) and someone with a slightly short rhythm (such as 22 hours). They both may entrain to the same 24-hour day, but the peak in body temperature might occur relatively late for the firs person (perhaps at 10 p.m.), whereas the peak would occur relatively early for the second person (perhaps around 6 p.m.).
Individuals with short biological rhythms hit their peak body temperature and alertness levels earlier in the day and, thus, begin to get sleepy earlier than do persons with longer circadian rhythms (Bailey & Heitkemper , 1991). A person with a 26-hour rhythm, would have a harder time getting up at 6 in the morning, because his or her 26-hour biological rhythm still has 2 hours to go, even though the 24hour clock is telling him or her to start a new day . A person with a 22-hour rhythm would have an easier time getting up early because he or she has completed a biological "day" in 22 hours and is ready to start another day even before the 24-hour clock is up.
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Body tempera ^wakeful
Do you know someone who you think is a morning type of person? What specific evidence makes you come to this conclusion? Do you think people with a morning type of rhythm are different in other ways from evening-type people? For example, are there other personality characteristics associated with being a morning type? Benjamin Franklin is quoted as saying that "early to bed, early to rise, makes a person healthy, wealthy, and wise." Do you think it is possible that morning types are actually wiser or that they have better outcomes in life? How would you design a study to answer this question?
Research on individual dif ferences in circadian rhythms provides the groundwork for understanding why some people are morning types and others are evening types. As you know, those with shorter biological rhythms tend to be morning persons, and those with longer biological rhythms tend to be evening persons. Horne and Ostberg (1976, 1977) developed a 19-item questionnaire to measure morningness-eveningness (see Table 7.3). The items ask about preferences for activities earlier or later in the day. In a sample of 48 participants, who took their body temperature every hour for several days, the researchers found that the scores on this questionnaire correlated - .51 with time of day that peak body temperature was reached. While the original study was done in Sweden, the negative correlation between self-reported preferences for activities in the morning and timing of peak body temperature has been replicated in the United States (Monk et al., 1983), Italy (Mecacci, Scaglione, & Vitrano, 1991), Spain (Adan, 1991, 1992), Croatia (Vidacek et al., 1988), and Japan (Ishihara, Saitoh, & Miyata, 1983).
These cross-cultural replications are consistent with the idea that preferences for morning or evening activities, and the time of day people are at their best, is a stable disposition with a biological basis. Scores on the Horne and Ostber g measure of morningness-eveningness are stable over time. Croatian researchers tested 90 college students on this measure and then tested them again seven years later , when they had finished college (Sverko & Fabulic, 1985). They found a significant positiv correlation, suggesting that the morningness-eveningness characteristic is fairly stable over time. There was, however, a general shift in the whole sample toward morning-ness, which might be expected in a group that moves from being college students to persons having jobs.
Many studies have been done on the validity of the morningness-eveningness construct. In one study (Larsen, 1985), college students completed a report every day for 84 consecutive days, stating what time they felt at their best each day and what time they got up and went to bed each day . The Horne and Ostber g questionnaire correlated strongly with average rise and retire times, as well as with the time of day the participants reported feeling at their best. The morning persons got up earlier , went to bed earlier, and reportedly felt at their best earlier , on average, than the evening persons.
What would happen if people who had to live together , such as college roommates, were mismatched on morningness-eveningness? One person likes to stay up late and sleep late, whereas the other likes to get up early , even on weekends, as well as go to bed early. How happy do you think these people would be with their rooming situation? This was the topic of a study by Watts (1982), who selected first-yea
Table 7.3 Items from the Morningness-Eveningness Questionnaire
Please read each question carefully before answering. Each question should be answered independently of others. Do not go back and change or check your answers.
All questions have a selection of answers. For each question, circle the number in front of only one answer. Please answer each question as honestly as possible.
1. Considering only your "feeling best" rhythm, at what time would you get up if you were entirely free to plan your day?
1. between 11:00 a.m. and noon
2. Considering only your "feeling best" rhythm, at what time would you go to bed if you were entirely free to plan your evening?
1. after at least 1:30 in the morning
2. between midnight and 1:30 a.m.
3. between 10:30 p.m. and midnight
3. On the average, how easy do you find getting up in the morning?
1. not at all easy
2. not very easy
3. fairly easy
4. very easy
4. How alert do you feel during the first half-hour after having awakened in the morning?
1. not at all alert
2. not very alert
3. fairly alert
4. very alert
5. How is your appetite during the first half-hour after having awakened in the morning?
1. very poor
2. fairly poor
3. fairly good
4. very good
6. When you have no commitments the next day (e.g., on weekends), at what time do you go to bed, compared with your usual bedtime?
1. more than two hours later
2. between one and two hours later
3. less than one hour later
4. seldom or never later
7. You wish to be at your peak performance for a test that you know is going to be mentally exhausting and lasting for two hours. You are entirely free to plan your day and, considering your own "feeling best" rhythm, which one of the four testing times would you choose?
Table 7.3 Continued
8. If you went to bed at 11:00 in the evening, at what level of tiredness would you be at that time?
1. not at all tired
2. a little tired
3. fairly tired
4. very tired
9. For some reason, you have gone to bed several hours later than usual, but there is no need to get up at any particular time the next morning. Which one of the following events are you most likely to experience?
1. will not wake up until much later than usual
2. will wake up at my usual time but will fall asleep again
3. will wake up at my usual time and will doze on and off for awhile
4. will wake up at my usual time and will not fall back asleep at all
10. Suppose that you can choose your own work hours. Assume that you worked a five-hour day and that your job was interesting and was paid by results. Circle the five consecutive hours you would work (circle five consecutive hours):
midnight 1 2 3 4 5 6 7 8 9 10 11 noon 1 2 3 4 5 6 7 8 9 10 11
11. At what single hour of the day do you think you reach your "feeling best" peak (circle one)?
midnight 1 2 3 4 5 6 7 8 9 10 11 noon 1 2 3 4 5 6 7 8 9 10
Source: Adapted from Horne, J. A., & Ostberg, O. (1976). A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. International Journal of Chronobiology, 4, 97-110.
college students living on the campus of Michigan State University . The participants had to have only one roommate. The roommate pairs completed the Morningness-Eveningness Questionnaire (MEQ), and they rated various aspects of their roommate relationship. Watts found that, the greater the dif ference between the roommates' MEQ scores, the lower ratings they gave to the quality of their relationship. Roommates who were very dif ferent on morningness-eveningness said that they did not get along very well with each other , that they did not enjoy their relationship and were not good friends, and that they were unlikely to continue living together . Differences on other personality dimensions, such as achievement motivation and competitiveness, did not predict such dissatisfaction with the roommate relationship. It appears that differences in morningness-eveningness are especially related to interpersonal compatibility problems.
Other studies of morningness-eveningness have looked at cognitive performance at different times of the day in relation to this personality disposition. Monk and Leng (1986) measured performance on a serial search task and a logical reasoning task at different times of day for participants classified as morning or evening types by th Horne and Ostber g questionnaire. Between the hours of 8 and 1 1 a.m., the morning types performed their best. Between the hours of 5 and 1 1 p.m., the evening types showed their best performance. Such dif ferences might be lessened through the use of stimulants, such as caf feine, as implied in the research of Revelle and colleagues (1980). Caf feine may help the performance of evening types most if taken in the morning, whereas it may help the performance of morning types most if taken in the evening. Persons can time their cof fee consumption to give them the greatest benefit given their morningness-eveningness disposition.
Being a morning type or evening type refers to preferences for time of day that may have a biological basis; however, sometimes situations occur that go against such preferences. Imagine a college student who is definitely an evening type, yet a clas he or she needs to take is of fered only at 8 a.m. or a morning type of person who takes a job in a factory and is assigned to the late shift (4 p.m. to midnight). Going against one's natural circadian preferences is dif ficult but not impossible. People d adjust to shift work and changes in sleep-wake schedule, and there is some evidence that evening types adjust to disruptions in sleep-wake cycles better than morning types (Ishihara et al., 1992). Such disruptions as transmeridian airline flights (which creat jet lag) or working all night without sleeping (i.e., pulling an all-nighter) may be better tolerated by an evening type than a morning type of person.
In summary, the preference for being active and doing important or demanding work earlier or later in the day may be rooted in the length of a person' s inherent biological circadian temperature rhythm. This is a good example of a physiological approach to personality because it highlights the notion of a behavior pattern (i.e., preference for different times of the day) being based on an underlying physiological mechanism (i.e., circadian rhythms).
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A Guide to Natural Sleep Remedies. Many of us experience the occasional night of sleeplessness without any consequences. It is when the occasional night here and there becomes a pattern of several nights in arow that you are faced with a sleeping problem. Repeated loss of sleep affects all areas of your life The physical, the mental, and theemotional. Sleep deprivation can affect your overall daily performance and may even havean effecton your personality.