ARI Research Note 86-64

"SLEEPABILITY" AND "WAKEABILITY" FOLLOWING SLEEP DEPRIVATION

00

N Peretz Lavie

SFaculty of Medicine Lfl Technion, Israel Institute of Technology

0

for

-* I

Scientific Coordination Office, London

Michael Kaplan, Chief

BASIC RESEARCH LABORATORY

Milton R. Katz, Director

&ELECTE

.- JUN 10 1986

U.S. Army A

Research Institute for the Behavioral and Social Sciences

May 1986

Approvecd for pubhc release, d-stribution un,rn,ted,

86 6 9 111
U. S. ARMY RESEARCH INSTITUTE

FOR THE BEHAVIORAL AND SOCIAL SCIENCES

A Field Operating Agency under the Jurisdiction of the

Deputy Chief of Staff for Personnel

WM. DARRYL HENDERSON

EDGAR M. JOHNSON COL, IN

Technical Director Commanding

Technical Review by:

Steve Kronheim

------- 4

This repor, as submitted by the contractor, he% been cleared fe release to Defense Technical Information Center

(DTIC) to comply with regulatory requirements. It has been given no primary distribution other than to DTIC

and will be available only through DTIC or other reference services such as the National Technical Information

Service (NTIS). The views. opini.nis, and/or findings contained in this report are those of the author(sl and

should not be construe as on official Cpitmerint of the Army position, policy. or decision, unless so designated

by other official documentation.

-h -- . --- . ... . . . . . ..- -..-.-. .---.---.-.-.-.-.- -. '................ ;;-'-'- . .. '-'V -
UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE ("hen Date Entered)

REPORT DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM

1. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

ARI Research Note 86-64 A ___/___'_____

4. TITLE (nd Subtitle) S. TYPE OF REPORT & PERIOD COVERED

"Sleepability" and "Wakeability" Final Report

Following Sleep Deprivation Period ending August 1982

6. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(e) 8. CONTRACT OR GRANT NUMBER(&)

Peretz Lavie DAJA 37-81-C-0237

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASK

Faculty of Medicine, AREA & WORK UNIT NUMBERS

Technion - Israel Institute of Technology 2QI61102B74D

Haifa, Israel

It. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

U.S.A.R.D.S.G. (UK) May 1986

Box 65 13. NUMBER OF PAGES

F.P.O. New York 09510 28 14. MONITORING AGENCY NAME & ADORESS(II dilferent from Controlilng Olice) 1S. SECURITY CLASS. (of thle report)

U.S. Army Research Institute for the Behavioral Unclassified

and Social Sciences, 5001 Eisenhower Avenue,

Alexandria, VA 22333-5600 1s. OECLASSIFICATION/DOWNGRADING

SCHEDULE 

- -

16. DISTRIBUTION STATEMENT (of thile Report)

Approved for public release, distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abetrect entered In Block 20, If different from Report)

It. SUPPLEMENTARY NOTES

Michael Kaplan, contracting officer's representative

19. KEY WORDS (Conlinue on reveree side If necesery and Identify by block number)

Sleep Deprivation 'Circadian Rythms,

"Sleepability" Reaction Time Task.

"Wakeability"

Ultradian Rythms

20. ABSTRACT (VC rert as re ere e t f It neces ,a, md Idertify by block number)

-This research note discusses experiments investigating the infrastructure of

arousal during the habitual waking day following one night of total sleep deprivation. Based on the data collected during the experiment, it can be concluded

that "wakeabilityr, the ability to remain awake, and "sleepability4 , the ability

to fall asleep, following sleep deprivation, are not complimentary processes,

but are probably governed by different mechanisms. The practical implications

of these results to the scheduling of replacement naps are discussed. 1\'II ,

DO I 1473 EDTIO OFI I NOV 6S IS OBSOLETE UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE (When Does Entered)

- . , . - . .% . . . . . . . . ... % . ,. .. .-. .... .. q . .. . .v: . . ... -..... .£ . .... ,-. ... .. %. ,-,... .,. ,... ... ,.. ,.- .. ,. ... .. . .
Introduction

The modern sophistication of weaponry systems demands from

combatant personnel complex operations which require alertness, precision, fast information processing and quick decision making. Usually

combat effort is concentrated in short time intervals during which there

is continuous military activity. Key limiting factors for such

continuous operation, beside unavoidable physical fatigue are accumulated

sleep loss and naturally occurring rhythmic variations in performance.

A large volume of research has demonstrated the operational consequences

of sleep loss on various aspects of human performance (e.g., Johnson,

1969; Johnson & Naitoh, 1974; Naitoh, 1969). Decrement in performance

because of sleep loss depends upon a complex interaction of factors such

as the nature of the task, its meaning to the performer, and the level of

the performer's motivation. Similarly the occurrence of natural rhythms

in human performance, mostly with a periodicity of about 24 hours/cycle

have been extensively studied and several books and symposia have been

dedicated to this subject (Alluisi and Chiles , 1967;

Colquhoun, 1971 ) Johnson, Topas, Colquhoun & Colligan, 1981).

Considerably less experimental effort has been addressed to the

investigation of short term rhythms in human performance and their interaction with sleep loss, which have been the subject of research in our

laboratory during the last few years. Detailed review of the existing

knowledge on ultradian rhythms has just been published (Lavie, 1982). Tn

a series of experiments carried out in the last two years, we have shown

that in certain tasks there are reliable short term variations in efficiency,

with periodicities centred around 1 hours. Such periodicities were clearly

seen in the accuracy of motor performance in subjects tested every 20 or

-l 1

, , . .- .-- , --. . . I . .. '- ' " . ... p 
-2-

10 minutes (Lavie, Gopher, Zomer & Fogel, 1981). One and a half hour

rhythms in the flow of urine measured in the same subjects were not

related to the rhythms in motor accuracy, suggesting that independent

oscillators regulate body fluids balance (Gopher F Lavie, 1980; Lavie 6

Kripke, 1977). In contrast to the rhythmic variations in movement

accuracy, the speed of movement did not show any rhythmicity, suggesting

that the short term rhythms in performance do not reflect the activity of 1

general non-specific "arousal" rhythm which would be expected to affect

speed as well as accuracy. Further support for this conclusion was provided by additional studies demonstrating lack of rhythmicity in a reaction

time task and only weak traces of 1l hour rhythmicity in a two-dimensional

tracking task (Lavie, Gopher, Zomer & Fogel, 1981). Since the rhythmicity

in movement accuracy was suppressed by immediate knowledge of results, we

hypothesized, as will be discussed later, that the rhythmicity in accuracy

reflected variations in the efficiency of short term memory storage

processes, mediated by underlying i!; hour rhythms in arousal processes.

!vidence for the existence of I! hour rhythmicity in arousal processes has been accumulated in several laboratories, including our own, over

the last several years. Ultradian rhythms in electroencephalographic

activity, particularly in the intensity of delta activity, typical of slow

wave sleep, were demonstrated in isolated and sleep deprived subjects by

Kripke (1972). Pupillary diameter and stability, traditional indices of

arousal levels, were also shown to vary rhythmically with the same periodicity (Lpvie, 1979). In an experiment just accomplished, as part of our

three-year series of experiments, we demonstrated that the I1 hour

rhythmicity in physiological arousal is indeed reflected in rhythmic variations in the ability to fall asleep during the day (Lavie & Scherson,
I

1981). Subjects instructed to attempt to fall asleep every 20 min, for

12 continuous hours (that is a 12-hour schedule of 15 min wake - 5 min

sleep) showed clusters of sleep stage I about every 1 hours. Sleep stage

1 is a transitional stage between wake and sleep. Sleep stage 2, on the

other hand, did not occur rhythmically, but showed a unimodal distribution

* with mid-afternoon peak around 1500 coinciding with the well-known "post

lunch dip" in performance (Blake, 1967). Selective REM deprivation as

well as total sleep deprivation modified the 1 hour rhythms as well as

the distribution of sleep stage 2. This effect of sleep deprivation on

stage 2 was rather impressive. Following sleep deprivation, instead of a

unimodal distribution of sleep stage 2, a bimodal distribution emerged

with a mid-afternoon sleepiness peak and an additional mid-morning peak.

These results have important theoretical and practical implications in view

of the intensive investigation of the role of restorative naps in alleviating the effects of sleep deprivation on combatant personnel (Naitoh, 1981;

Pinges, et al., 1981).

In light of these unexpected findings our research effort during

1981/82 was directed at investigating the influence of sleep deprivation

on the ultradian rhythmicity in the ability to fall asleep during the day,

and the interaction between these rhythms and performance.

MIethod and Design

Subjects:

Twelve subjects, aged 22 to 28, all veterans of combat units of the

IDF, participated in the study. They were healthy, and with normal sleepwake habits, as determined from two-week sleep diaries and from two nights

pre-experimental whole-night polyhypnographic sleep recordings.

* . .% . .... .~ . . . . . . . . . . . . . .. . . . . . . . . . . . .**. .~ .*

.....-... ~. *...... . . -
4-

Experimental Procedure:

1) Adaptation to the laboratory - each of the subjects spent two nights

in the laboratory for adaptation purposes. Polyhypnographic recordings

(EEG, FOG. EMG, and respiration to exclude breathing abnormalities in

sleep) were obtained from 2300 until 0700, on the second night only.

2) Baseline - Subjects come to the laboratory at 2200, after a normal day

without naps. Polyhypnographic recordings began at 2300 and continued

until 0700 the next day, as during the adaptation night. The day-experiment began at 0720 and lasted for 16 consecutive hours,

From 0720, a precise 13 min - wake, 7 min - sleep schedule was begun,

and was maintained for 48 consecutive 20-min periods (16 hours, until 2300).

Fvery 13 min, subjects were instructed to lie in bed, close their eyes,

and attempt to fall asleep. Polyhypnographic recordings (FFG, EOG, and EMG)

were performed during the 7-min "sleep attempts". If subjects were asleep

at the end of the 7-min period they were awakened, and the lights were

turned on. The 13:7 wake-sleep schedule was chosen to approximate the

normal 2:1 wake-sleep ratio (16 h. wake, 8 h. sleep).

During the 13-min scheduled wake time subjects were disconnected from

the polygraph and were requested to leave the bedroom. At about the

middle of the wake period they performed two tests: "Add 7" and a combined

one-hand, and coordinated two-hands, reaction time task. In the first task

subjects had to sum up as many pairs of 3 digit numbers and to add 7 to the

sum , as they possibly could in 60 seconds.

The second task was one or two handed coordinated reaction time tasks.

In this type of task, after a "go" signal, subjects simultaneously initiate

two-handed movements to targets of disparate or equal difficulty and distance
,iw -br -w -. -i m

(Kelsom Southard & Goodman, 1979). The apparatus consisted of a riexiglas base (76 cm long, 16 cm wide and 2 cm thick), mounted on a standard

table. Two contact switches, centred 0.5 cm apart served as the home

keys (see Fig. 1 for a schematic representation of the apparatus). The

four targets were positioned along the longitudinal center line of the

base, two large targets (7 cm in diameter) at a distance of 22 cm from

the home keys, and two small targets (3.5 cm in diameter) at a distance of

4 cm from the home keys. A single target was used in the one handed condition, and two targets were used in the two handed conditions. A red light

emitting diode served as the warning signal, and similar diodes mounted

above the targets served as the "go" signal and designated the targets.

Stimuli presentation and data collection w'ere controlled by a PPP 11/34

minicomputer.

Subject's task was to move his index finger from the home keys to the

target as fast and as accurately as possible, after receiving the "go"

signal above the appropriate target . The "go" signals were given 1 sec

after the warning signal. Five combinations were presented in each 20

min session: 1) right hand "near " target 2) right hand 'far" target 3) two

handed "near " targets, 4) two handed "far" targets, and 5) right hand "far"

combined with left hand "near " targets . Each of the combinations was

presented 5 times with an average intertrial interval of 5 sec. The order

of presentations was randomized and two practice trials, which were not

included in the final analysis, were presented at the beginning of each

session. If subject missed the target, that trial was excluded and another

trial was presented by the computer.

In each trial, both reaction times (the time from the "go" signal to

the release of the home keys) and movement times (the time from the release
-Sa40 46

IsI

Fg 1:Schematic representation of the one hand and two-handed

reaction time apparatus.
of the home keys until reaching the targets) were registered by the

computer. Reaction times greater than 800 msec or less than 90 msec, and

movement times less than 30 msec or greater than 600 msec, were excluded

from the final analysis.

From the 5 trials of each combination, mean reaction time and movement time were computed. Since there were two one-hand conditions and 3

two-handed conditions, there were 8 separate means for each session.

Since, however, performance of the two hands were highly correlated across

time, the number of data points could be reduced by averaging across experimental combinitions.

3) Sleep Deprivation - "sleep" condition (SC)

In this part of the experiment subjects came to the laboratory at

2000, at least a week after the completion of the previous part of the

experiment (e.g. the design was balanced across subjects in such a way that

6 subjects performed initially SC, and then RS, and 6 subjects were tested

in the reverse order). They spent the night awake in the laboratory reading,

listening to music, etc. under close observation of an experimenter. No

polygraphic recordings were performed and food was available ad libitum.

Then, at 0720 the experimental schedule of 13-min-wake, 7 min-sleep was

initiated for 16 hours for 8 subjects. As before, a monitored

recover>' sleep followed the experimental day. Behavioral testing was conducted during the 13 min scheduled wake periods. For the other 4 subjects

the experimental schedule was continued for 24 consecutive hours until 0700

the next morning.

4) Sleep Deprivation - "Resist Sleep" Condition (RS)

In this part of the experiment subjects came to the laboratory at least

one week after the completion of the previous part. They spent the night

9 , - " "' -"."-" '."- , "- -' - ". ' " ", " ".- -"- - .," ", . , . . " ' -" " " "" ""V "
-7-

awake in the laboratory from 2000 until 0720 as in SC. Then, at 0720,

a precise experimental schedule of 13-min-wake outside the bedroom,

7 min awake in bed with eyes closed, was initiated for 16 hours, for 8

subjects. In this experimental condition, every 20 min subjects were

instructed to enter the bedroom, to lie in bed and to close their eyes,

and to try to remain awake for 7 min. At the end of the 7 min, if asleep,

they were awakened, the lights weic turned on, and they were instructed

to enter the testing room, where they remained for the scheduled 13 min

wake period. Polyhypnographic recordings were performed during the 7 min

"in bed" periods. To increase subjects' motivation to resist sleep, extra

monitary bonuses were promised for the three best performing subjects;

e.g. the three subjects with the maximum amount of wake time.

Behavioral testing was conducted during the 13 min scheduled wake

periods as before, and a polygraphically monitored recovery sleep followed

the 16 h experimental period. As in the SC experiment, for 4 subjects the

experimental schedule was continued for 24 consecutive hours until n700 the

next morning.

D .. 
8-

Results

Temporal structure of "sleepability" and "wakeability" - Fig. 2 presents

the mean histograms of total sleep (stage 1 + stage 2 + stages 3 F 4 +

stage REM) per 7 min (in percentages) in each of the 3 experimental conditions: baseline, SC and RS, for the 8 subjects tested fir 16 hours (from

0720 until 2300). Obviously, under both sleep deprivation experiments

total sleep during the day was considerably higher than during baseline.

There was no significant difference, however, between the amounts of

sleep stage 1 and 2 in the two experiments (see Table 1). (Overall means

of stage 1 and stage 2 for those 8 subjects were 26.38% and 18.9%). In

spite of the similarity in the overall neans, there was, however, a clear

phase difference between the two mean curves. The mean curve for the SC

experiment peaked at 0800 and then five hours later at 1300, while the

mean curve for the RS experiment peaked an hour later at 0900 and then at

1420. That is, although in both conditions the interpeak interval was S

hours, the peaks were delayed by about one hour when subjects attempted to

remain awake rather than to fall asleen. Under both conditions, sleep

decreased toward the evening hours, reaching a minimum at 18-1900.

Ten frequencies spectral analysis confirm the eye ball analysis. Fig.

3 presents the average spectra for stage 1 and stage 2 in the baseline,

SC and RS experiments. The average spectra for stage 1 in the baseline

experiment peaked at the fast ultradian frequencies of 21.6 and 25.6 c/day,

corresponding to periodicities of about 67 to 57 min/cycle. This spectral peak however was not statistically significant. In the SC and RS

experiments, average spectra for stage 1 peak at the slow ultradian

. ." . . . .
C4,

-4.

00

cIn
- 8b -

Stage I

Percentages Occurrences

Subject BL RS Sc BL PS SC

Avi. 1.51 21.21 34.7 6 29 40

Gid. 2.42 17.07 15.08 8 41 45

Ami. 9.7 16.44 23.1 31 42 47

Pan. 9.3 401.23 25.95 24) 46 47

Ari. 3.02 22.3 15.1 i4 45 35

Day. 4.91 31.93 ,1 V ,4

Fhu. 3.75 31.4 - 42

Ore. 2.95 23.-4 237! 42

x 4.68 2 ;8 - : "" "

Sd 3.12 Q.31 t. 4 , 4 4.

Percentages uccurrenceSubject BL Rs SC RI RS Sc

Avi. 0 10.3 10.o 0 is 19

Gid. 0 22.08 26.4 0 38 38

Aini. 0 21.6 21.1 () 37 35

Dan. 0 23.29 17.81 0 39 35

Ari. 0 13.95 15.3 0 16 19

Dav. 0 23.07 20.6 0 34 33

Ehu. 0 13.5 24.59 0 24 33

Ore. 0 23.49 26,1 0 26 35

x 18.91 20.31 0 28.62 30.87

Sd 0 5.38 5.54 0 9.76 7.49

Table 1: Average percentages and occurrences of sleep stage 1 and 2

for each subject in the three parts of the study.

-.................................-.....
W V- Sc -

d 0/0

15-

5

z

100

n I 1 I •

0 7.2 14.4 21.6 28.8

FREQUENCY (cycles/day)

Fig. 3: Average spectra for stage 1 (upper panel) in the BL(....),

RS(-) and SC(---) conditions, and for stage 2 (lower panel)

in the RS(-) and SC (---) conditions. Significant Peak

_. -......-- ..,.* .......... *,-- . . . . -... .
-9-

at

frequencies of 7.2 c/d and/18-21.6 c/day, but neither peak approaches

-statistical significance. Average spectra for stage 2 in the RS condition

significantly peaked at 3.6 c/d, corresponding to a dominant periodicity

of about360 min/cycle. Average spectra for stage 2 in the SC condition

peaked at the zero frequency indicating a predominant linear trend in

the data. In summary, spectral analysis confirm the existence of slow

ultradian periodicity in the occurrence of sleep stage 2 in the PS condition. The periodicity was less evident in the SC experiment.

The slow ultradian rhythmicity in sleepiness was particularly

striing in the data of the 4 subjects who were studied for 24 hours

again in the RS experiment. All subjects showed prominent slow rhythmicity in their amounts of total sleep and sleep stage 2; representative

data are presented in Figs. 4A and b,which display the amounts of sleep

stage 2 per 7 min for 2 of the 4 subjects. Both showed two diurnal peaks

in sleep stage 2, at 0900-1000 and at 1600-1700, and a prominent nocturnal

peak. Interestingly enough, in subject Da there was a monotonic

decrease in sleep stage 2 toward the early morning hours, suggesting a

dominant circadian effect.

Similar to the 8 subjects who were tested for 16 hours only, the

rhythmicity in sleepiness in the SC experiment was less pronounced and

more variable than in the RS condition . In all subjects, however, there

was a clear nocturnal peak of sleepiness. Spectral analysis confirmed the

visual impression by demonstrating a clear and significant spectral peak

at 3.6 cycles day in the RS condition. Corresponding to a periodicity close

to 6 hour/cycle, no significant peaks were evident in the baseline or SC

experiments for these four subjects.
- 98 -

. . ar r r

A 

L

30

30

0

7 II 23 IS 3 7

T"U

Fig, 4A B: Slow ultradian cycles in the percentages of sleep

stage 2 in two subjects tested for 24 hours. Please

note the similarity between the two rhythms.

l-1
-10-

Reaction time task

The type of task utilized in the present study enabled the

examination of ultradian rhythmicity in several aspects of performance,

separately. First, the effects of sleep deprivation and ultradian

rhythmicity on reaction time and movement time could be examined. Based

on our previous findings (Lavie et al. 1981), we anticipated ultradian

variations in movement time hut not in reaction time. Second, since in

each of the 20-min sessions, both simnle tasks (one hand reactions) and

complex tasks (disparate two-handed reactions) were presented, the interaction between sleep deprivation and ultradian rhythmicity, and task

complexity and difficulty, could therefore be examined. In this renort

we will focus on the rhythmicity in performance of selected combinations

and the interaction of this rhythmicity with the rhythms in sleep.

Reaction time and movement time

There was a marked difference between the temporal structure of the

reaction time and movement time across the 24-hour experimental periods.

In most subjects reaction times were stable, with minimal deviations

from the mean level. In some test periods there was a linear increase in

reaction time, which was particularly evident in the 4 subjects tested

for 24 hours. Figure SA, B & C present the reaction time data of one

subject (pooled across all 5 combinations or across all 20 trials in

each session) for the baseline, RS and SC experiments. Spectral analysis

confirms the lack of significant rhythmicity in the reaction times.

Furthermore, the complexity of the task did not affect the temporal

structure of the data, although preliminary analysis revealed some effects

of the task complexity on the overall mean reaction time.

............................-.-
.4

S PS ExpwuflbI

43

7 I

TV

Fig. SA, B C. Reaction time data of one subject in the three parts

of the experiment. Spectral analysis did not reveal

significant rhythmicity besides the nocturnal increase

in reaction time.
- 11

In a marked contrast to the stability of the reaction time performance,

there were clear slow ultradian variations in movement time, particularly

in the RS experiment, that correspond to the variations in arousal.

Figures 6A, B and C present the movement time data of the same subject

whose data for RT are shown in Fig. 5 for the one hand ("far" right

condition), the left hand in the disparate two-handed condition, and for

the average movement time for all conditions (N=20). The rhythmicity in

the data is clearly seen in all three combinations. Peak movement times

(%vhich correspond to decrease in performance) occurred at 1100, 1720 and

at 0420. Comparison of Figs.6A and 6B revealed that the rhythmicity in

movement time was more pronounced in the performance of the left hand in

the two-handed disparate condition, than in the one-hand condition; the

corresponding coefficients of variation (standard deviation/mean x 100)

were 46% and 34%, respectively. The same rhythmicity was shown in the RS

experiment by most of the subjects. Fig. 6D presents the average movement

time for another subject investigated for 24 hours. This subject showed

peak movement times at 1120, 16-1700 and 0300.

Correlating the sleep data with the movement time data clearly

revealed that peak movement times coincided with peak sleepiness. This is

clearly evident from comparing Fig. 4 and Figs. 6ABC and D which present

the sleep data and movement time data of the same subject. Obviously the

cycles are synchronized with each other.

The rhythms in movement time were less obvious in the SC experiment.

Figs. 7A and 7R present the average movement time in the SC experiment for

the same subjects whose data in the RS condition were presented in Figs.

6ABC and 6D The variations in performance are clearly less regular and

there is no phase relationship between the two curves , except for the

common decrease in performance during the night time.

Spectral analysis, cross-spectral phase angle analysis are presently
- hla -

TIla

.26.

22-

.14

z .10 J

ww

0

.14-

7 111 923 3

Fig. 6AB C: Slow ultradian rhythms ir, movement time of the right

hand in the "far right" condition (A), the left hand in the disparate

two-handed condition, (B), and in the mean performance of all conditions

pooled together (C).

Fig. 6D: Slow ultradian cycles in the mean movement time of another

subject. Please note the similarity between the cycles in 6AB g C and 6D.

V

,b.
36-

32 SC Expetmwri

U 24-

~-16-

z

w 12-

~14-

7 11523 3

Fi.7A B Mean movement times (pooled acrcss all trials; for

two subjects in the SC condition. The data of 7A corresnz n to

6ABC, and the data of 7B correspond to the data of 6D.
1 -12

performed to determine the dominant periodicities in performance and

the phase relationship between performance and arousal levels.

Performance - "Add 7"

There was a very marked practice effect from baseline to the first

sleep deprivation experiment but there was no significant difference

between SC and RS in the overall performance levels. The means were 6.23,f 62,

and 9.46 for baseline, SC and RS respectively. Spectral analysis did not

reveal any consistent spectral peaks in any of the experiments.

Discussion

The results of the present studies clearly confirm our prediction

that under sleep deprivation conditions the fast ultradian rhythmnicity in

sleepiness is modified toward a slow rhythmicity. Such 4-6 hour rhythmicity

during the daytime hours was clearly evident in the RS experiment, which was

most dramatically evident in the 4 subjects investigated for 24 consecutive

hours. Clearly the rhythmicity in arousal affects performance; the variations in movement time, but not in reaction time or in the "add 7"' performance, were synchronized with the amounts of sleep. The independence of the

reaction time performance and calculation performance from the rhythms in

sleepiness support our previous conclusion that the ultradian rhythms in

arousal affect only some aspects of performance, which are probably related

to short term memory processes and selective attention (Gopher & Lavie, 1980).

The difference between the RS and SC experiments was rather interesting

dand to some extent even unexpected. In spite of the fact that there was no

significant difference between the two experiments with respect to the overall amounts of sleep stage 1 and 2, there was a phase difference between
- 13 -

the respective sleepiness curves. In the SC experiment the first peak

in sleepiness appeared 1 hour earlier than in the RS experiment. However,

even more interesting, comparing the data of the 4 subjects investigated

for 24 hours to the data of the 8 subjects investigated for 16 hours

suggest that the length of the experiment clearly affects the temporal

structure of the vigilance stages across the day. In the 24-hour experiment there was a marked suppression of the slow ultradian rhythmicity as

compared with the/s5hexperiment. This clearly suggests that knowledge

about the length of the sleep deprivation period, and subjects motivation

(to remain awake, or to fall asleep) can drastically modify the structure

of daytime vigilance stages. This last conclusion has both theoretical

and practical implications. One of the immediate recommendations, based

on the present results, is that recuperative naps following sleep deprivation should be spaced S-6 hours apart. Furthermore, it appears that llOOh

and 1700h are the appropriate "windows" for such naps. Optimal timing of

recuperative naps should take into consideration the endogenous cycles in

vigilance curves. Also, it appears that providing accurate information

about the length of the expected sleep deprivation appears to be important

for the prediction of the prospective "deeps" in arousal, or the appearance

of irresistable sleep periods. The clearest and most regular cycles appear

when subjects were investigated for 24 hours and were required to resist

sleep. The cycles were considerably less clear when they were given 7 -min

sleep attempts.

t ; , "...." ""'"'"" ... -t -,"- ", ,' "- °'" '' " '' .... . .. ''"."-........"..."......,..-...."..-
-14-

In recent years, there has been a great interest in the question of

what are the optimal times for sleep. It has been shown, for instance,

that sleep during the descending portion of the temperature cycle is longer

than sleep during the ascending portion of the cycle (Wever, 1979).

In spite of the general agreement that napping has beneficial effects in

preventing some of the long term deterioration of performance during sleep

deprivation, little is known about the optimal timing of such recuperative

naps. This question appears highly important in light of the observations

that immediate performance upon awakening from a nap may show no improvement and furthermore, may be even lower than the pre-nap levels. langdon

and Hartman (1961) were the first to demonstrate loss of performance efficiency after sudden awakening from nocturnal sleep. The post-awakening sleep

inertia is usually short-lasting and has been estimated to last about

IS min (Wilkinson & Stretton, 1971). It is quite possible, then, that a

recuperative nap, taken at the wrong biological time, may cause a more severe

and longer period of sleep inertia, mal:ing the nap disadvantageous for

behavioral efficiency. Preliminary support for the dependence of the length

and severity of sleep inertia on the timing of the nap was provided by

Naitoh (1981). He showed that the recuperative power of naps taken at the

early morning hours (0400-0600) was considerably lower than the recuperative

power of a midday nap (1200-1400). Further than that , Naitoh concluded

that one 2-hour midday nap, taken after 53 hours of wakefulness, was as

recuperative as the combined action of two 2-hour naps taken doring the

early morning hours and midday, after a shorter period of wakefulness. The

reason for the lower recuperative power of the early morning nap was the

long and more severe post-nap sleep inertia.

--- S. ~ . . . . - . . . -%
- 15 -

We found significant slow ultradians only in the RS study, 

It has been widely accepted that increased motivation tends to counterA.ffect decrement in performance dt1e to sleep loss, and to minimize 

circadian vanations in ,_performance, \)'ilY.inson, ([961) & Blake, (1971) 

demonstrated that the variation ir, performance over the day of a letter 

cancellation task is dramatically reduced by an incentive. This was provided by giving subjects immediate kno1,·1edge of results, after each test 

s2ssion, in the presence of all mer.1bers of the group. The resultant 

hightened state of motivation in the group dramatically reduced the magnitude of the diurnal variations in performance. Chiles, Alluisi and Adams 

(1963) have also demonstrated this "dampening" effect of raised motivation 

or, the c:unplitude of circadian perfornance variation. Gopher ~ Lavie (1981) 

derconst::·ated sinilar effects 1..-ith respect to ultradian r!"!ythmicity. 

Int:1ediate kno1dedge of results suppressed the 14.4 c/day ultradian rhythmicity in a perceptual motor tasl:. 

In 1 ig!--.t of this dampening effect, in the present study increased 

motivation had an opposite effect. It emphasized and consolidated the slo~ 

ult;:adian rh;·thmicity in sleepiness and perfornance, The 361) mil'! periodicity in sleepiness ~as significant only in the SR condition, ~here su~jects 

were p;:ornised monitary re~ards if they managed to stay a~ake. 

A militarily realistic regime is one h'hich der.1ands several days of 

continuou~ activit)', follo~ed by a period of less intense activity, during 

...,·hich short periods of rest may be possible. Haslam (1~31) de!:lol'!strated 

that even small amounts of scheduled sleep are beneficial to nilitary 

iJersonne l involved in continuous performance. That is, sleep loss effects 

over prolonged periods of sleep de?rivation can be minini:ed by offering 

limited amounts of sleep. 1l1e question no\\· is ho"'· much sleep and at "·hat 

time. 

BEST AVAILABLE COPY 
Rr It

I.:

-16-

Our present results demonstrated that during the habitual waking

hours there were two periods of irresistable sleep: at 8-11 and 16-18

hours. On the other hand, sleep could easily be avoided at 12-14and 19-22.

Therefore, one can predict that the recuperative power of naps taken at q

and 17 will be greater than the recuperative power of naps taken at 13

or 20 . Hlence our study for the first time provides some guidelines for

determining the optimal timing for daytime naps.

-St

1 - " ' ,,- ,!" in n i " ,"F ._ - . , ' ' " . ,'/ ', - .' '. . . ,'- '. /,] ' J '," , _ '__ 
- 17 -

References:

Alluisi, E.P. and Chiles, W.D. Sustained performance, work-rest scheduling

and diurnal rhythms in man. Acta Psychologicas 1967, 27, 436-442.

Blake, M.J.F. Time of day effects on performance in a range of tasks.

Psychom. Sci. 9, 349-350, 1967.

Blake, M.J.F. Temperament and time of day. In: Biological Rhythms and

Human Performance. W.P. Colquhoun (Ed.) London: Academic Press, 1971.

Chiles, W.D., Alluisi, E.A. & Adams, 0. Work schedules and performance during

confinement. Human Factors, 10, 143-196, 1968.

Colquhoun, W.P. Circadian variations in mental efficiency. In: Colquhoun,

W.P. (Ed.), Biological rhythms and Human Performance. Academic Press:

London, 1971.

Dinges, D.F., Orne, E.C., Evans, F.J. & Orne, M.T. Performance after naps

in sleep-conductive and alerting environments. In: Johnson, L.D., Tepos,

D.I., Colquhoun, W.P. and Colligan, M.J. (Eds.), Biological Rhythms,

Sleep and Shift Work. Spectrum Pub., New York, 513-538, 1981.

Gopher, D. and Lavie, P. Short term rhythms in the performance of a simple

motor task. J. Mot. Behav., 1980, 12, 207-221.

Haslam, D.R. The military performance of soldiers in continuous operations:

Exercise "Early Call" I and II. In: Johnson, L.C., Tepos, D.I.,

Colquhoun, W.P. and Colligen, M.J. (Eds.), Biological Rhythms, Sleep

and Shift Work. Spectrum Pub., New York, 435-438, 1981.

Johnson, L.C. Psychological and physiological changes following total sleep 'm

deprivation. In: A. Kales (Ed.), Sleep: Physiology & Pathology.

Philadelphia: Lippincott, 206-220, 1969.

Johnson, L.C. and Naitoh, P. The operational consequences of sleep deprivation and sleep deficit. (AGARDograph No. 193), London: Technical

Editing and Reproduction Ltd., 1974.

..............
- 18 -

'18

References cont.

Johnson, L.C., Tepos, D.I., Colquhoun, W.P., and Colligan, M.J. (Eds.).

Biological Rhythms, Sleep and Shift Work. Spectrum Pub., New York,

1981.

Kripke, D.F. An ultradian biological rhythm associated with perceptual

deprivation and REM sleep. Psychosom. Ned., 1972, 2, 221-234.

Langdon, D.E. & Hartman, B. Performance upon sudden awakening. USAF

report, 1961.

Lavie, P. Ultradian rhythms in alertness - a pupillographic study.

Biol. Psychol., 1979, 9, 49-62.

Lavie, P. & Scherson, A. Ultrashort sleep-wake schedule. 1. Evidence of

ultradian rhythmicity in "Sleepability". EEG & Clin. Neurophysiol.,

1981, 52, 163-174.

Lavie, P. & Kripke, D.F. Ultradian rhythms in urine flow in waking humans.

Nature, 1977, 269:142-144.

Lavie, P., Gopher, D., Fogel, R. & Zommer, J. Ultradian rhythms in

perceptual motor tasks. In: Johnson, L.C., Tepos, D.I., Colquhoun,

W.P., and Colligan, M.J. (Eds.), Biological rhythms, Sleep and Shift

Work, Spectrum Pub., New York. 133-144, 1981.

Lavie, P. Ultradian rhythms in human gleep and wakefulness. In: W.B. Webb

(Ed.), Biological Rhythms, Sleep and Performance. John Wiley & Sons:

-London, 239-271, 1982.

Naitoh, P. Sleep loss and its effects on performance. U.S. Navy Medical

Neuropsychiatric Research Unit. Tech. Rep. No. 68-3, 1969.

• d ., . ') ., .' ., , . . ,,... . .o. .'. € .' .. - .. . ,, . ... . . ..
o'' .4 .- ~ -J ~-~,~~ ' ' - Fr.*- -. . . - *. j r. ~U ~a

- -19-

Naitoh, P. Circadian cycles and restorative power of naps. In: L.C.

Johnson, D.I. Tepos, W.P. Colquhoun, and M.J. Colligan (Eds.)

SI Biological rhythms, sleep and shift work. Advances in Sleep Research,

vol. 7, SS3-580, 1981.

Wever, R.A. The Circadian System in Man. Springer-Verlag: New York, 1979.

* Wilkinson, R.T. & Stretton, M. Performance after awakening at different

times of night. Psycho. Sci. 23, 283-285, 1971.

Wilkinson, R.T. Interaction of lack of sleep with knowledge of results,

repeated testing, and individual differences. J. Exp. Psychol., 62,

263-271, 1961.

F2

4%i

in....- ., ... Vj--o