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\title{Effects of Sleep Deprivation \\
{\small (or, What Every MIT Student Knows, but Never Measured)}}
\author{Marc Horowitz}
\date{11 December 1995}
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Anyone who has stayed up all night knows that sleep deprivation has
negative effects.  Studies have shown that sleep deprivation makes one
more prone to fall asleep and less able to concentrate on a task
(Mullaney, et al, 1983).  Continued sleep deprivation causes
perceptual distortions (Babkoff, et al, 1989) and physiological
discomfort (Mullaney, et al, 1983).  Experiments have determined the
relative effects of time and circadian cycles on sleep deprivation
effects (Babkoff, et al, 1983), and demonstrated how some of these
effects can be reduced (Tilley, et al, 1988, and Mullaney, et al,
1983).  Studies have also demonstrated that it is possible to reduce
the amount of sleep a person gets without significantly affecting
performance (Horne and Wilkinson, 1985).

Mullaney, et al. (1983) performed an experiment which studied many
aspects of sleep deprivation.  Three groups of subjects were brought
into a lab, where each group engaged a different sleep schedule over a
48 hour period starting at each subjects' usual bedtime (around
midnight).  All three groups slept for six hours.  The first group
(``42-straight'') then remained awake for 42 hours.  The second group
(``6-and-1'') stayed awake for six hours, then slept for one,
repeating this for the remaining 42 hours.  The third group
(``18-and-6'') stayed awake for 18 hours, slept for six hours, and
stayed awake for the last 18 hours.

While awake, all subjects worked 90\% of the time (except for food and
bathroom breaks) on three computer-based experiments to measure
performance.  The first required the subject to track a target on the
computer screen with a joystick.  The second displayed three patterns
to the subject, who had to determine which two matched.  In the third,
the subject added two three-digit numbers and gave the answer.
Subjects also periodically rated their own sleepiness.  During the
entire experiment, while subjects were asleep and awake, EEG and EOG
(eye movement) recordings were taken of the subjects, to note what
stage, if any, of sleep the subject was in.

This experiment noticed four different major kinds of sleep
deprivation effects, all of which were most pronounced in the
42-straight group.  As time progressed, members of this group rated
themselves as becoming significantly more sleepy.  This was
corroborated by measurements of the subjects falling into
``microsleeps'', slow wave sleep periods of ten seconds.  On average,
each person experienced 80 microsleeps (consecutive 10 second periods
spent asleep counted as multiple microsleeps).  Performance on the
various tests was also affected by lack of sleep.  In particular,
performance on the addition test, which required the highest level of
concentration and cognitive performance, declined substantially over
the 42 hours of measurement.  These subjects also reported minor
physiological problems, such as nausea, and aches and pains.  The last
major effect of sleep deprivation is sensory distortion, particularly
visual distortion.  By the end of the experiment, 80\% of the subjects
in the 42-straight group had reported visual distortions or
hallucinations of some sort.

The effect of time on the various effects was not entirely linear.
Circadian cycles can be clearly observed in the experimental data.
Microsleeps were almost nonexistent until 11pm, when the subjects
normally went to sleep, when they started increasing, peaking between
6am and 8am, which is the deepest trough of the circadian cycle.
Addition performance dropped substantially starting at 11pm, but
actually began to increase again for a few hours starting at 9am the
next morning.

Although Mullaney, et al. did not note when perceptual distortions
occurred, other researchers have studied this.  Babkoff, et al. (1989)
studied the contributions of linear time effects and circadian cycles
of sleep deprivation on perception.  Over 72 hours of sleep
deprivation, starting at 6am, subjects spent between 30 and 45 minutes
an hour in testing.  Logs of perceptual events during these sessions
were kept by the subjects and the experimenters.  Numerical analysis
of the number of subjects experiencing such events during each four
hour period was performed.  About 40\% of the variation could be
accounted for by a linear effect (increasing over time), and almost
50\% of the variation could be accounted for by a 24-hour cycle which
peaked between midnight and 4am each night.  This study also noted
that perceptual effects earlier and more frequently were distortions
related to the tasks being performed (``the monitor screen is growing
sprouts of grey and green hair all over'') than with more general
non-task related hallucinations (``the decaying corpse of Barbara
(assistant) interfered with vision during the (administration of) oral
mood scale'').

Not surprisingly, the best way to avoid sleep deprivation effects is
to get a reasonable amount of sleep every night.  But how much is
reasonable?  Horne and Wilkinson (1985) studied the effects of chronic
sleep reduction over a six week period.  A group of subjects who all
had habitual, consistent nightly sleep of about eight hours was
divided into two groups.  The control group was asked to maintain
their normal sleep patterns.  The experimental group was asked to
decrease their duration of sleep night from eight hours to six hours
gradually over a four week period, and to maintain this level for two
more weeks.

Subjects recorded the times at which they slept, and evaluated their
own sleepiness daily using a standard questionnaire.  Once a week
during the study, near the end of the week, lab measurements to
determine sleepiness and concentration were made between 1pm and 4pm,
which is the time during daytime during which people who need sleep
are most likely to be tired.  Near the end of the six weeks, each
subject spent one night in a sleep lab to measure the characteristics
of his or her sleep.

For the entire duration of the experiment, most measurements of
sleepiness and concentration were not significantly different between
the control and experimental groups.  The one exception was that the
experimental group reported being more sleepy after lunch for a few
days after each reduction in sleep duration, but the subjects adjusted
to this in less than five days, before any laboratory measurements
were taken.  The sleep lab measurements did note that onset of sleep
was more rapid in the experimental group.  This group had sleep
interrupted less often, and recalled fewer dreams than the control
group.

These results are especially significant when compared to the results
of experiments where sleep duration was reduced more than two hours.
Carskadon and Dement (1981, cited in Horne and Wilkinson, 1985) found
that subjects who reduced their sleep to five hours a night for a week
were increasingly sleepy during the day as the week progressed.  Webb
and Agnew (1974, cited in Horne and Wilkinson, 1985) found that
subjects who reduced their sleep to 5.5 hours a night for two months
had a steadily decreasing ability to concentrate on tasks.  It seems
that a reasonable amount of sleep on average is six hours a night, or
a reduction by two hours, but no less.

If it is not possible to sleep six hours a night, there are other ways
to increase performance.  The first is by taking naps.  In the study
by Mullaney, et al. (1983), the 6-and-1 group of subjects took a one
hour nap every seven hours.  For the first half of the experiment,
this group was less sleepy and performed better on all tasks than the
other two groups.  However, the measurements of the members of this
group were less consistent, exhibiting a kind of ``sleep inertia''
which increased sleepiness and reduced performance for the first hour
after waking up from each nap.  For the second half of the experiment,
the 6-and-1 group did better (was less sleepy and performed better)
than the 42-straight group, but not as well as the 18-and-6 group.
The members of the 6-and-1 group experienced on average 69 microsleeps
during the experiment, which is less than the 42-straight group, but
much more than the 18-and-6 group, whose members experienced an
average of 27 microsleeps.  Only 40\% of these subjects reported
perceptual distortions.  Twenty percent of the 18-and-6 group
experienced some perceptual distortion.

Tilley and Bohle (1988) measured how exercise reduced the effects of
sleep deprivation.  During a high school all-night marathon
disco-dancing fundraiser for charity, a group of volunteers took a 20
minute break each 2 hours to participate in reaction time tests which
measured concentration.  As a control, the subjects spent one night
each a week before and after the marathon in a lab doing the same
tests in a non-exercise situation.  The average reaction time was
significantly shorter on the night when the subjects were exercising
than when they were not.  In addition, the variability of the response
was much lower with exercise, especially between 4am and 6am, which is
the time when performance is normally lowest.  The increased
performance is probably due to the reduction in drowsiness associated
with the raised metabolic rate caused by exercise.

Experiments on sleep deprivation clearly show that reduced sleep
affects many aspects of behavior and perception.  As sleep deprivation
continues, concentration and awakedness decrease, especially during
the time when one would normally be sleeping.  The body can tolerate
extended periods of time with somewhat reduced sleep duration, but
even if a good night's sleep is not possible, short naps help increase
performance.  Periodic exercise will also help one remain alert and
awake.

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\bf\Large References
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Babkoff, H., Sing, H.C., Thorne, D.R., Genser, S.G., and Hegge, F.W.,
(1989).  Perceptual distortions and hallucinations reported during the
course of sleep deprivation.  {\em Perceptual and Motor Skills, Vol
68,} pp. 787-798.

Carskadon, M.A., and Dement, W.C., (1981).  Cumulative effects of
sleep restriction on daytime sleepiness.  {\em Psychophysiology, Vol.
18,} pp. 107-113.

Horne, J.A., and Wilkinson, S., (1985).  Chronic Sleep Reduction:
Daytime Vigilance Performance and EEG Measures of Sleepiness, With
Particular Reference to ``Practice'' Effects.  {\em Psychophysiology,
Vol. 22, No. 1,} pp. 69-78.

Mullaney, D.J., Kripke, D.F., Fleck, P.A., and Johnson, L.C., (1983).
Sleep Loss and Nap Effects on Sustained Continuous Performance.  {\em
Psychophysiology, Vol. 20, No. 6,} pp. 643-651.

Tilley, A.J., and Bohle, P., (1988).  Twisting the night away: the
effects of all night disco dancing on reaction time.  {\em Perceptual
and Motor Skills, Vol 66,} pp. 107-112.

Webb, W.B., and Agnew, H.W., (1974).  The effects of a chronic
limitation of sleep length.  {\rm Psychophysiology, Vol. 11,}
pp. 265-274.

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