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increase in memory-test scores in that experimental condition. Then in the second
row, put an X in each box where you think the participants perceived an improvement
in their memory.
The Results
When Anthony Greenwald and his colleagues (1991) conducted this study—with
cassette tapes at that time—they asked two questions: (a) Did the memory recording
actually work, and (b) did participants perceive that they worked? The key results are
presented in the table below. First, scores on the objective memory test were no
higher for those who listened to the subliminal memory recording than for those given
the self-esteem recording. Second, participants perceived that their memory had
improved—but that perception was based on which label was on the recording, not
on which message the recording actually contained. People may believe in the power
of the hidden message, but the recordings themselves had no real effect. Other
research has shown that subliminal weight-loss recordings also are ineffective
(Merikle & Skanes, 1992).
What Does It All Mean?
Ever since psychology was born as a discipline, questions have been raised
about consciousness and the extent to which we are influenced by information that is
not in awareness. If you predicted that the subjects in this study did not benefit from
subliminal self-help messages, you were right. (You were also right if you predicted
that they believed the recordings to be effective, illustrating the power of suggestion.)
If you think, however, that people are not in other ways subject to influence without
awareness, stay tuned to the rest of this chapter. To fully understand the human
organism, we must account for both what we attend to in our normal waking lives and
the effects of sleep, dreams, hypnosis, and other less conscious processes.
What does it mean to be conscious? Is consciousness achieved only during
wakefulness? Are we conscious when we sleep or when we dream? In many ways,
having consciousness is an incredible achievement. It relates to our recognition not
only of the environment within which we live but also of ourselves and our actions
within our environment. In this chapter, we’ll find that human consciousness ranges
on a continuum from an alert waking state of attention to varying depths of sleep,
dreams, hypnosis, and the “altered” states produced by psychoactive drugs. We’ll
also find that the more we know about consciousness, the more able we will be to
regulate our own states of mind.
ATTENTIONAL PROCESSES
LEARNING OBJECTIVES
Describe the nature of consciousness and the selectivity of what we attend to and
are aware of in our environment.
Define consciousness.
Explain whether people can attend selectively to one stimulus among many
and the mechanism by which stimuli we try to block out still register on the mind.
Outline the mechanism that enables people to divide their attention so that
they can engage simultaneously in more than one activity.
Discuss how we are influenced by stimuli that never register in our
awareness.
The word consciousness has many different meanings, but psychologists tend to
define it in terms of attention—a state of awareness that consists of the sensations,
thoughts, and feelings that a person is focused on at a given moment. As implied by
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this definition, consciousness has a limited capacity. Whether you are mentally
focused on a memory, a conversation, a foul odor, this sentence, or your growling
stomach, consciousness is like a spotlight. It can shift rapidly from one stimulus to
another, but it can shine on only one stimulus at a time. Try free associating into a
recording device some time, and you’ll find yourself mentally straying in what William
James (1890) called the stream of consciousness.
consciousness. An awareness of the sensations, thoughts, and feelings that one
is attending to at a given moment.
attention. A state of awareness consisting of the sensations, thoughts, and
feelings that one is focused on at a given moment.
Consciousness may be limited and the mind may wander, but three important and
adaptive processes are at work. First, attention is selective—so, to some extent,
people can control consciousness the way they control the channels of a television
set. Second, for tasks that require little conscious effort, people can divide their
attention and simultaneously engage in more than one activity. Third, even when
people are conscious of one stimulus, they are also capable of reacting to other
stimuli in the environment, which suggests that we can process information outside of
awareness. As we’ll explore, these features enable us to widen, narrow, and move
the spotlight of consciousness as needed (Pashler, 1998; Phillips, 2019).
Selective Attention
Picture this scene. You’re standing at a cocktail party with a drink in one hand and
a spring roll in the other. In the background, there’s music playing, as well as the
chatter of voices. You’re in the middle of a conversation with a friend when suddenly
you overhear two other people talking about someone you know. Can you tune into
the gossip and still carry on a conversation? How easy is it to attend selectively to
one stimulus among many?
In a classic test of this cocktail party phenomenon, Colin Cherry (1953)
presented subjects wearing headphones with two different messages, played
simultaneously, one to each ear. In this dichotic listening task, subjects were told to
“shadow”—that is, follow and repeat aloud, word for word—only one of the two
messages. Were they able to do it? Yes, especially when the competing messages
were different, as when one featured the voice of a man and the other the voice of a
woman. But what happened to the message that subjects had filtered out and
ignored? Later, subjects could not recall any of it. Even when they were stopped in
the middle of the presentation and asked to repeat the unattended message, their
ability to do so was limited. Through a process of selective attention, people can
zoom in on a single auditory stimulus, but then they lose track of competing auditory
stimuli.
cocktail party phenomenon. The ability to attend selectively to one person’s
speech in the midst of competing conversations.
selective attention. The ability to focus awareness on a single stimulus to the
exclusion of other stimuli, as in the cocktail party phenomenon.
To examine selective attention in another sensory modality, Ulric Neisser and
Robert Becklen (1975) devised a visual analog of the dichotic listening task. They
simultaneously showed subjects two videotapes, one superimposed over the other.
One tape showed three people passing a basketball, and the other showed two
people playing a hand-slapping game (illustrated in Figure 4.1). The task was to keep
track of one game or the other. As in the shadowing study, subjects could attend to
only one stimulus at a time. In fact, the filtering process was so complete that out of
24 subjects who were focused on the basketball players, all but one failed to notice
that the hand slappers had stopped their game at one point to shake hands. When
the researcher later replayed this segment, these subjects were shocked at what they
had missed. This result illustrates that information may be included or excluded from
consciousness through a process of selective attention.
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Description
Figure 4.1 Selective Attention
Source: Neisser, U., & Becklen, R. (1975). Selective looking: Attending
to visually specified events. Cognitive Psychology, 7(4), 480–494.
https://doi.org/10.1016/0010-0285(75)90019-5
Divided Attention
Our consciousness may be limited, but the filtering process does not immediately
or completely block out all of the extraneous information. In dichotic listening
experiments, for example, most subjects do manage to hear the mention of their own
names (Moray, 1959). They also manage to hear sexually explicit words, and words
they had learned to associate with electric shock—even when these are irrelevant
stimuli spoken in the unattended ear. Many subjects in this situation could tell that
something odd had occurred in the unattended ear when the speech in that ear was
switched from ordinary English to English played backward (Wood & Cowan, 1995).
Recent studies also show that people make rapid eye movements to examine the
world around them, and that our eyes are naturally drawn to objects that are novel,
bright, colorful, moving, and abrupt in their appearance—even, at times, when these
stimuli intrude on another task in which we are engaged (Pashler, Johnston, &
Ruthruff, 2001). As Jan Theeuwes and colleagues (1998) put it, “Our eyes do not
always go where we want them to go” (p. 379).
Is it possible, despite our selective tendencies, to divide attention among
competing stimuli? Can you simultaneously watch TV and read a book, or drive a car,
listen to the radio, and carry on a conversation? It depends on how much conscious
effort is needed for the various tasks. Consider driving. When first learning to drive,
you have to concentrate on how to operate the steering wheel, gas pedal, and brake,
and on how to monitor traffic and watch for pedestrians, signs, and lights. At that
point, driving is so effortful an activity that even the radio is distracting. As you gain
more experience behind the wheel, however, driving then becomes an automatic
process that does not require high levels of effort or awareness or your undivided
attention. Once that happens, you can drive, listen to music, and talk to others in the
car all at the same time (Simons-Morton & Ehsani, 2016; Treisman, Viera, & Hayes,
1992).
Is it safe to talk on the phone while driving? Researchers examined the phone
records of 699 motorists who were in accidents and who had cellular telephones. The
accident rate was four times higher when drivers were on the phone than when not—
even with hands-free headsets. A recent large-scale survey of U.S. drivers found that
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g y
texting while driving was associated with increased crash rates and while this was
true across all age groups, it was highest among younger drivers. Driving may be a
largely automatic process, but people need to stay alert to traffic and other changing
conditions—which is why most states now prohibit motorists from talking on the
phone while driving.
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The distinction between effortful and automatic processing explains how people
are able to exhibit divided attention when at least one competing task is “on
automatic.” It’s easy to walk, talk, and chew gum simultaneously, but for most of us it
is difficult to play chess while watching TV. Consider the attention required to perform
the complex motor behaviors needed in sports. When you first learn a sport—like
baseball, basketball, hockey, or soccer—you tend to monitor every move you make.
Then as you get better and more experienced, your movements become so
automatic that you don’t have to think about timing, breathing, head position, followthrough, and other mechanics. Experienced athletes should thus be able to divide
their attention while performing in a way that novices cannot. To test this hypothesis,
Sian Beilock and colleagues (2002) observed experienced and novice golfers putting
on an indoor green, then experienced and novice soccer players dribbling through
cones in a slalom course. In both studies, the experienced athletes were better able
to maintain their performance while attending to a competing auditory task. Today,
many sports teams use a variety of cognitive training methods to develop the working
memory and attention of athletes to improve sporting performance and abilities in
other tasks even outside of sports, although the effectiveness of such trainings is
mixed (Harris, Wilson, & Vine, 2018).
divided attention. The ability to distribute one’s attention and simultaneously
engage in two or more activities.
We have a canny ability to perform many skills at one time. Here a performer rides
a unicycle and juggles at the same time.
iStock.com/double_p
A classic study on divided attention was devised in 1935 by John Stroop, using a
test aptly called the Stroop test. When Stroop first presented his subjects with 100
colored items, he found that the task in which participants were presented with blocks
of color to name took an average of 63 seconds, whereas the task in which
participants were presented with words in colored font took 110 seconds—a 74
percent slowdown in performance time.
Stroop test. A color-naming task that demonstrates the automatic nature of highly
practiced activities such as reading.
Researchers have used the Stroop test in hundreds of experiments, and they
continue to debate the reasons for this effect (MacLeod, 1991; Scarpina & Tagini,
2017). Still, one conclusion is clear: Experienced readers process word meanings
automatically, without effort or awareness. It just happens. And because the test
words contradict the colors (when they don’t, performance is quicker), reading
interferes with the color-naming task (Brown, Gore, & Carr, 2002). Past experiments
also show that personally relevant and emotionally provocative words interfere with
color naming more than neutral words do. Thus, people diagnosed as having a fear
of spiders are highly disrupted by words such as crawl and hairy, while those overly
concerned about their health are disrupted more by cancer and blood (Williams,
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Mathews, & MacLeod, 1996). In a study of people who had been physically injured in
a serious automobile accident, those who were traumatized by the experience were
slowed more than those who were not by such words as wreck, crashed, and totaled
(Beck, Freeman, Shipherd, Hamblen, & Lackner, 2001).
Influence Without Awareness
Whereas Wilhelm Wundt and William James pioneered the study of conscious
processes, Sigmund Freud theorized that people are driven more by unconscious
forces. Freud argued that there are three levels of awareness in the human mind:
conscious sensations, thoughts, and feelings that are currently in the spotlight of
attention; preconscious material that is temporarily out of awareness but is easy to
bring to mind; and an unconscious reservoir of material that is suppressed, banned
from awareness. According to Freud, people are influenced by material that resides
outside of awareness. Was he right?
For years, many researchers were skeptical of this claim. But then an outpouring
of new studies brought unconscious processes to the forefront of modern psychology.
These studies suggest that people can be influenced in subtle ways by subliminal
messages—information that is presented so faintly or so rapidly that it is perceived
“below” our threshold of awareness (Bornstein & Pittman, 1992; Merikle, Smilek, &
Eastwood, 2001; Ruch, Züst, & Henke, 2016). Let’s consider some examples that
illustrate the point.
subliminal message. A stimulus that is presented below the threshold for
awareness.
Mere Exposure
One powerful principle of attraction is called the mere exposure effect: The more
often you see a stimulus—whether it’s a word, an object, a melody, or a face—the
more you come to like it (Zajonc, 1968). This type of learning begins even before
birth, with mere exposure to the flavors of foods in a mother’s diet being later
preferred by newborns, and children learning to like novel (i.e., new) flavors simply by
increased exposure to them (Trabulsi & Mennella, 2012). But must you be aware of
the prior exposures for this effect to occur? Not always (Privitera, 2016; Yagi & Inoue,
2018). After all, as stated, even a fetus shows signs of mere exposure learning. In a
typical study with children and adults, subjects are shown pictures of geometrical
objects, each for only 1 to 5 milliseconds, which is too quick to register in awareness
—and too quick for anyone to realize that some objects appear more often than
others. After the presentation, subjects are shown each of the objects and asked two
questions: Do you like it? Have you ever seen it before? Perhaps you can predict the
result. The more frequently presented the object, the more subjects like it. And when
asked if they’ve ever seen the liked objects before, they say no. This pattern of
results demonstrates the mere exposure effect, even without awareness (Bornstein,
1992; Huang & Hsieh, 2013; Zajonc, 2001).
Priming
Have you ever noticed that whenever a novel word slips into conversation, it
suddenly gets repeated over and over again? If so, then you have observed priming,
the tendency for a recently presented concept to “prime” responses to a subsequent
“target” question. Thus, when subjects are asked to decide if the letters D-O-C-T-O-R
form a word, they are quicker to say yes if the previous item was N-U-R-S-E than if it
was A-P-P-L-E (Meyer & Schvaneveldt, 1971). What if the prime word is presented
subliminally, below our threshold of awareness? When that is done, the result is the
same—even when the prime word is presented so quickly that subjects could only
recall seeing a flash of light (Marcel, 1983). In fact, subliminal presentations of drawn
objects, such as hammers, chairs, and dogs, can be used to prime the identification
of similar objects that are shown up to 15 minutes later (Bar & Biederman, 1998).
priming. The tendency for a recently presented word or concept to facilitate, or
“prime,” responses in a subsequent situation.
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Priming can be any stimulus, even images, that can influence your behavior. For
example, images like the one shown here, depicting delicious-looking fruits and
vegetables, can be used to prime healthy eating.
iStock.com/Aiselin82
In a series of provocative experiments, Tanya Chartrand and John Bargh (1999)
found that motivations and emotions are also subject to automatic influence without
awareness. In one study, subjects took part in a “word search” puzzle that contained
either neutral words or words associated with achievement motivation (strive, win,
compete, succeed, master). Afterward, they were left alone and given 3 minutes to
write down as many words as they could generate from a set of Scrabble letter tiles.
When the 3-minute limit was up, subjects were signaled over an intercom to stop. Did
subjects, driven to obtain a high score, stop on cue or continue to write? Through the
use of hidden cameras, the experimenters observed that 57 percent of the subjects
primed with achievement-related words continued to write after the stop signal—
compared to only 22 percent in the control group.
In a second study by Chartrand and Bargh (1999), subjects took part in a
“reaction-time” task in which they were subliminally exposed to words that evoked
strongly positive emotional reactions (music, friends), strongly negative reactions
(cancer, cockroach), or more neutral—only mildly positive and negative—reactions.
Afterward, they described their current mood state as part of what was supposed to
be an unrelated experiment. Subjects were not aware of the words they had “seen” in
the first task. Yet compared to those in the neutral-word groups, those previously
exposed to positive words were in a happier mood, and those exposed to negative
words were in a sadder mood.
SLEEP AND DREAMS
LEARNING OBJECTIVES
Explain why sleep is a necessary function for many mammals, including humans.
Discuss whether people, like animals, are influenced by biological rhythms or
whether they are flexible in their sleeping schedules.
Outline how researchers study sleep in the laboratory.
Differentiate among the stages of sleep and identify what makes REM sleep
so special.
Explain what dreams are, why we have them, and what they mean.
Distinguish among common sleep disturbances and approaches suggested
to address them.
It may start with a deep yawn. Then the eyelids begin to fall. Then your head
drops and you get that drowsy sense of calm before nodding off, tuning out, and
calling it a day. For most people, falling asleep is a pleasurable experience. Why?
What is sleep? Why do we need it? And what about dreams—what purposes do they
serve and what, if anything, do they mean? The average person spends about 8
hours a day sleeping and 90 minutes dreaming. Given an average life expectancy of
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75 years, that amounts to about 25 years of sleep and 5 years of dreaming in a
lifetime. Yet until recently, we knew very little about this important aspect of our lives.
Shakespeare once referred to sleep as “the death of each day’s life.” Others, too,
think of sleep as a state of complete dormancy. They are wrong. As we’ll learn, the
sleeping brain is humming with activity (Dement & Vaughan, 1999; Grandner, 2019).
The Sleep-Wake Cycle
Many birds migrate south for the winter. Bears and raccoons hibernate. Certain
plants open their leaves during the day and close them at night—even if kept in a
dark closet. As biological organisms, humans are also sensitive to seasonal changes,
the 28-day lunar cycle, the 24-hour day, and the 90-minute activity-rest cycle that is
linked to variations in alertness and daydreaming. These and other regular
fluctuations are forms of biological rhythms.
biological rhythm. Any periodic, more or less regular fluctuation in a biological
organism.
From a psychological standpoint, one internal clock is particularly important: Every
24 hours, we undergo a single sleep-wake cycle. This cycle and others that take
roughly a day to complete are referred to as a circadian rhythm. Humans tend to be
most active and alert during the middle of the day, when body temperature peaks,
and least active and alert at night, when body temperature drops to its low point. The
human circadian rhythm is also evident in fluctuations in blood pressure, pulse rate,
blood sugar level, potassium level, growth hormone secretions, cell growth, and other
physiological functions (Lavie, 2001; Pilorz, Helfrich-Förster, & Oster, 2018).
circadian rhythm. A biological cycle, such as sleeping and waking, that occurs
approximately every 24 hours.
Everyone is influenced by circadian rhythms, but everyone’s inner clock is set
somewhat differently. Think about yourself. Are you a morning person or a night
person, a lark or an owl? If you had a choice, would you rather wake up at 6, 8, or 10
o’clock in the morning? How easy is it for you to work late into the night? During what
time of day are you most productive? These kinds of questions can be used to
determine your circadian rhythm (Hasan et al., 2012). Although morning types fall
asleep earlier at night and awaken earlier in the morning, most people adapt as
needed to the schedules they must keep. Still, it helps to know when you’re likely to
be at your best. When subjects were tested for memory at 9 AM, 2 PM, and 8 PM,
the larks performed worse as the day wore on, whereas owls performed better
(Anderson, Petros, Beckwith, Mitchell, & Fritz, 1991; Malone, Patterson, Lozano, &
Hanlon, 2017). Among college students, up to 60 percent suffer from poor quality
sleep (Schlarb, Friedrich, & Claßen, 2017), although larks are more likely than owls to
take early morning classes—and they earn higher grades in those classes (Guthrie,
Ash, & Bendapudi, 1995). Among older people, who tend to prefer early-morning
hours, performance on learning and memory tasks declines when they’re tested late
in the day (Intons-Peterson, Rocchi, West, McLellan, & Hackney, 1999). Across a
whole range of cognitive activities that require vigilance, research shows that people
perform better during their “preferred” time of day (Malone et al., 2017; May &
Hasher, 1998).
Is the circadian rhythm endogenous (set by an inner clock), or is the human body
responsive to outside patterns of lightness and darkness? Ask Stefania Follini, an
Italian interior designer. In January 1989, she descended into a Plexiglas bunker
buried in a cave in New Mexico. Sealed off from sunlight, outside noises, changes in
temperature, schedules, and clocks, she lived alone in this underground home for
131 days—a “free-running” period of time that allowed her body to establish its own
rhythm. Her only link to the world was a personal computer. When Follini emerged
from her isolation in May, she thought it was only March. Her “day” had extended to
25 hours, then to 48. As time went on, she slept and woke up later and later. She
stopped menstruating, ate fewer meals, and lost 17 pounds.
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Stefania Follini steps inside the underground bunker where she lived alone for
131 days.
Thomas Ives / ContributorThomas Ives / Contributor
Other volunteers were similarly isolated for extended periods of time. Some
settled naturally into a “short” day, but most free-ran on a longer cycle that averaged
25 hours. With each successive cycle, these subjects tended to go to sleep a little
later and to wake up a little later (illustrated in Figure 4.2). Body temperature and
hormone levels tended to follow the same rhythm. Like Follini, these subjects drifted
toward a longer day—then underestimated the amount of time they had been
isolated. When reexposed to sunlight, the subjects readjusted their biological clocks.
Where is this timing device? Animal experiments have shown that the circadian
rhythm is controlled in the brain’s hypothalamus, just above the optic nerves, by two
pinhead-size clusters of neurons called the suprachiasmatic nuclei, or SCN. How do
the SCN function? You may recall from Chapter 2 that light passing through the eye is
converted to neural signals and sent to the cortex through the optic nerve. Apparently,
some of these optic nerve axons—and the information they convey about light—are
diverted to the SCN. Nestled in the center of the brain, the pea-shape pineal gland
also plays an important role. As darkness falls, the pineal gland produces melatonin
—a hormone that facilitates sleep by letting the body know that it’s dark outside.
When light strikes the retina, melatonin secretion is slowed down. As we’ll explore
later, melatonin is often used to treat chronic insomnia (Auld, Maschauer, Morrison,
Skene, & Riha, 2017).
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Description
Figure 4.2 The Inner Clock
The circadian rhythm is synchronized like a fine watch by an interplay between
the brain and environmental cues. But what happens when your rhythm is disrupted?
One common source of disruption is air travel—specifically, flying across time zones,
which throws your body out of sync with the new time of day and causes you to sleep
at the wrong time. If you’ve ever flown from one coast to the other or overseas, then
you may have suffered jet lag, a condition that makes you feel tired, sluggish, and
grumpy. Most people find it easier to fly west, which lengthens the day, than to fly
east, which shortens it. Because the body naturally drifts to a longer day, this makes
sense. Flying westward goes “with the flow” rather than against it. Consistent with this
analysis, research shows that long-distance travel within a time zone does not cause
jet lag (Ambesh et al., 2018).
In recent years, researchers have tested various strategies that long-distance
travelers can use to combat jet lag. Many tips and suggestions can help you get a full
night’s rest (National Sleep Foundation, 2018). For example, always get a full night’s
sleep before a long trip. Anticipate your new time zone. Drink lots of liquids to avoid
dehydration, but avoid alcohol, which disrupts later sleep. If you plan to travel east—
say, from Los Angeles to New York—you can facilitate the adjustment process by
sleeping earlier than normal before you leave so that you more closely “fit” the lightdark cycle of the new time zone. As soon as you board the plane, set your watch to
your destination’s time zone and eat and sleep accordingly. Because of studies that
indicate that bright-light exposure at night speeds the resetting of the inner clock,
researchers also advise that, upon arrival, you spend the first day outdoors.
Can anything more be done to prevent jet lag from gripping us as we cross time
zones in flight? In 1998, Scott Campbell and Patricia Murphy published an article in
Science on a technique for combating jet lag by resetting our internal clock. They
reported that by shining a light on the backs of people’s knees, they were able to shift
the clock that regulates the sleep-wake cycle. Because the backs of the knees
contain blood vessels just under the skin, they reasoned, it was possible to send a
chemical timing signal through blood circulating through the body, not just through the
eyes. Subsequent research, however, casts doubt on the claim. In a study also
published in Science, Kenneth Wright and Charles Czeisler (2002) measured
changes in the levels of melatonin in 22 subjects over a 10-day period. Some
subjects were exposed to bright light behind the knee but not in the eye; others were
exposed to light in the eye but not behind the knee; still others received no light. The
result: The circadian clock was shifted by light to the eyes—but not by light to the
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back of the knee. Today, it is widely recognized that more research is needed to
combat jet lag (Ambesh et al., 2018).
To combat jet lag, exposure to light can help to adjust the body clock to a new
time zone through controlled exposure to bright light, and it can even improve your
mood.
iStock.com/Rocky89
Night Work, Sleeping, and Health
We humans are diurnal creatures—active during the day and asleep at night.
Thus, we like to work from 9 to 5 and then play, sleep, and awaken to the light of a
new day. Yet an estimated 25 percent of all Americans—including truckers,
emergency-room doctors and nurses, security guards, police officers, factory
workers, and telephone operators—are often forced to work late-night shifts
(American Psychological Association, 2020a). The question is, what is the effect? Do
people adapt over time to shift work and other late-night activity, or does it
compromise their health and safety?
Both biological and social clocks set the body for activity during the daytime and
sleep at night, so it’s no surprise that many shift workers struggle to stay alert. People
who choose night work tend to fare better than those assigned on a rotating-shift
basis (Barton, 1994). Still, shift workers in general get fewer hours of sleep than day
workers, complain that their sleep is disrupted, and report being drowsy on the job.
Often they blame their lack of sleep on ringing phones, crying babies, traffic, and
other daytime noises. Part of the problem too is that the body’s internal alarm clock
tries to awaken the day sleeper. Either way, the adverse effects can be seen at work
—where night-time energy levels are low, reaction times are slow, and productivity is
diminished. In a survey of 52 flight controllers of the International Space Station,
nearly half of night-shift workers sampled reported disordered sleepiness while on
shift (Mizuno et al., 2016). Can anything be done to lessen the dangers posed by shift
work? Koh Mizuno and colleagues (2016) recommend rotating shifts more often to
maximize the number of days between shifts (to reduce the number of consecutive
shifts), increasing the number of shorter breaks (5 to 10 minutes per hour), and
improving working conditions (to reduce stressors during a shift). Consistent with
these suggestions, studies show that it seems to take two days of rest, not one, for
workers to fully recover from their nocturnal routine (Totterdell, Spelten, Smith,
Barton, & Folkard, 1995). Charles Czeisler and colleagues (1990) found that the
realignment of the circadian rhythm can also be speeded up by exposing shift
workers to bright levels of light in the workplace and to 8 hours of total darkness at
home during the day. Within a week, the body’s biological clock can be reset and the
health risks of night work reduced. It takes only 4 hours of bright-light exposure one
night to improve performance the next night (Grønli & Mrdalj, 2018; Thessing, Anch,
Muelbach, Schweitzer, & Walsh, 1994).
The National Highway Transportation Safety Administration estimates that up to
6,000 fatal traffic accidents a year are sleep related—and, according to the Traffic
Safety Foundation, 37 percent of all drivers have dozed off at least once while behind
the wheel. Overall, 1 to 3 percent of highway crashes in the United States are caused
by driver sleepiness—a problem that most plagues young drivers, shift workers,
drivers who use alcohol and other drugs, drivers with sleep disorders, and
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