The effects of lunch time napping on habitual nappers’ mental work efficiency in the afternoon and early

doi:10.4236/health.2009.14046

Paper Menu >>

Journal Menu >>

Vol.1, No.4, 284-289 (2009)

doi:10.4236/health.2009.14046

SciRes

Health

The effects of lunch time napping on habitual nappers’

mental work efficiency in the afternoon and early

evening: an empirical study from China

Guang-Jin Zhang1, Fei-Fei Sun2, Jian-Qiao Liao3

1Politics and Law School, China University of Geosciences, Wuhan, China; hbzgj@126.com

2Faculty of Foreign Languages, Jiangxi University of Finance and Economics, Nanchang, China

3Management School, Huazhong University of Science and Technology, Wuhan, China

Received 27 September 2009; revised 5 November 2009; accepted 11.November 2009.

ABSTRACT

30 college students who have the habit of lunch

time napping (LTN) participated in experiments

under two different conditions: Having lunch

time napping and not having lunch time napping.

They were asked to complete three tasks in-

cluding vigilance reaction, short-term memory,

addition arithmetic; their performance was re-

corded automatically by computer during 3 dif-

ferent periods in the afternoon and early eve-

ning. The analysis about the experimental data

showed that: as for habitual nappers, midafter-

noon nap zone existed, LTN played a very im-

portant role in overcoming it, and did great help

in enhancing their vigilance in the afternoon and

early evening, however, LTN didn’t bring sig-

nificant positive effect to executing complex

tasks (such as short-term memory and addition

task) at the periods of time 16:30-17:30, 20:00-

21:00. Finally, this article discussed the conclu-

sions and its significance.

Keywords: Lunch Time Napping; Mental Work

Efficiency

1. INTRODUCTION

Lunch time napping is very prevalent in China. The

farmers often take LTN only in summer because they

need avoid the hot sun’s radiation at noon; however,

more and more mental workers also take LTN, moreover,

they usually take LTN all the year round, which can’t be

explained by the weather. An investigation in a univer-

sity found that 71% teachers and 78% students are used

to taking LTN more than 10 months a year; the respon-

dents admitted that they won’t perform well or work

efficiently in the afternoon and evening without LTN.

However, LTN also induced a lot of controversies, some

people think that it leads to low work efficiency for that

the continuity of eight hours work a day is interrupted by

LTN. Besides, LTN extends the time between going to

work and getting off work, especially for those whose

home is far away from work site, such as the work time

of not having HTL is often from 9:00 to 17:00, otherwise,

it is usually from 8:00 to 17:30, which makes people feel

more tired [1]. Dose not having LTN really lead to ha-

bitual nappers’ mental work inefficiency?

To look for the answer from former researches, there

were two difficulties. Firstly, Chinese literature usually

only describes people’s subjective feeling, few of them

studies the effects of LTN based on the actual work per-

formance. Secondly, in most of relative English litera-

ture, the napping time is often in the afternoon or in the

evening, even in a few of researches about LTN, the du-

ration of napping is very short, which is not consistent

with the situation of China. For example, Macchi, Bou-

los and Ranney et al. studied the effects of afternoon nap

on nighttime alertness and performance [2]. McEvoy &

Lack studied the effects of nap (happens in the night

shift) on work efficiency [3]. Mednick, Nakayama and

Cantero et al. studied the restorative effects of afternoon

naps on perceptual deterioration [4]. Backhaus & Jung-

hanns studied effects of afternoon nap on memory ability

[5]. Milner, Fogel and Cote studied the effects of after-

noon nap on motor performance and the moderation ef-

fects of habitual napping between them [6]. Hayashi et

al. studied the effects of both afternoon nap and lunch

time nap on mood, performance and EEG activity [7-8].

Driskell and Mullen made A Meta-Analysis about the

efficacy of naps as a fatigue countermeasure [9]. Almost

all the naps studied mentioned above in the afternoon,

which is the working time in China, the working time in

the afternoon in China is often from 14:00 to 17:30 or

14:30-18:00. LTN is a common phenomenon in China,

and the napping duration is usually as long as 1 hour to

1.5 hours (12:30-13:30 or 12:30-14:00). Therefore, the

context about the western scholars’ researches is far dif-

ferent from Chinese reality, the conclusions of those

G. J. Zhang et al. / HEALTH 1 (2009) 284-289

285

researches can’t be simply applied to practice in China.

For the two pieces of reasons above, this research is to

study the effects of LTN on habitual ‘nappers’ mental

work efficiency in the afternoon and early evening

through experiment.

2. METHOD

2.1. Subjects

30 college students (18 females and 12 males) partici-

pated in the experiment. These subjects have the habit of

lunch time napping, they have lunch time napping at

least 4 times a week, and more than thirty minutes each

time, their night sleep is often from 23:00 to 7: 00, they

are healthy and don’t have the habits of smoking and

heavy drinking. They did not take any drug during the

experiment; meanwhile, all subjects are voluntary and

given payment.

2.2. Procedure

The experiment is a balance intra-group design, that is,

the 30 subjects were simple randomly divided into two

groups with the same number. Each group participated

once in two kinds of condition experiment（Having LTN

and not having LTN), in order to eliminate the possible

influence of the shift experimental condition on work

efficiency in the next day, the two tests under different

experimental condition which each group subjects par-

ticipated in were conducted at one week interval. In par-

ticular, half of the subjects firstly participated in the ex-

periment under the condition of having LTN, and then

took the second test under condition of not having LTN

one week later; the other half took the first test under not

having LTN condition, and then took the second test

under having LTN condition after a week.

In this study, the two kinds of experimental conditions

are having LTN and not having LTN. The former is to let

the subject have lunch time napping in dormitory from

12:30 to 14: 00, and arrive at the lab at 14:25. The later

is to let the subjects arrive at the lab by 12:30, and they

can do anything except taking naps until 14:25. In the

week before the first experiment test and the week in-

terval between the two experiment tests, the subjects

were required to take normal night sleep and lunch time

napping everyday, and to keep daily log so as to be

checked. In order to let the subjects be familiar with and

proficient at the experimental tasks, in the morning of

the day before the first experiment test, all subjects par-

ticipated in the instructions of the experiment and took

15 minutes practice for the three experimental tasks.

Each experiment includes three periods. The first pe-

riod lasts from 14:30 to 15:30, the second period lasts

from 16:30 to 17:30, and the third period is from 20:00

to 21:00. During the experiment, the subjects were not

allowed to leave the laboratory except for having supper

outside, they can read novel, play games or chat in the

laboratory between the three periods. The reason for the

first period design is that most organizations in China

require their employees to start work at 14:30 in summer;

the second period and the third period are to measure the

effects of LTN on work efficiency before off duty in the

afternoon and in the early evening.

In each period of the experiment, all subjects need

accomplish three tasks: vigilance reaction, short-term

memory, addition arithmetic, after each task there will be

five-minute rest. As for the task of vigilance reaction, it

needs the subjects response to 40 signals; as for the task

of short-term memory, it needs the subjects recall 20

groups of English letters; as for the task of addition, it

needs the subjects judge whether right or not about 30

equations of pairs of three-digit number addition. It will

take about one hour to finish all the three tasks.

In order to motivate the subjects to participate in the

experiment seriously, we had clarified that better per-

formance and more payment.

2.3 Experimental Task

This study chose three typical mental workers as the

experimental tasks.

One of the experimental tasks is vigilance reaction.

This experimental task is completed on the computer.

There is a clock designed by the researcher on computer

screen, and the clock is the same as the one in our daily

life. There is only one exception that its second hand

occasionally walked 2 grids, and the requirement for

subjects is to press the “Del” button in low right corner

of the keyboard when the second hand walked 2 grids,

then the computer would automatically record the sub-

ject’s response. During the experimental task, the prob-

ability of second hand randomly walked 2 grids was 0.02,

in other words, the second hand walked 2 grids once

about on the average of 50 seconds, the probability is

very appropriate, for if it is too small, signals appeared

little, it would make subjects divert attention easily; if it

is too large, signals appeared much, this would lead to

the loss of the vigilance reaction characteristic. Since the

second hand walked 2 grids is a random event, so within

30 minutes on each subject’s computer screen, the num-

ber of signals was different, therefore, and the rate of

wrong response was to evaluate the level of vigilance for

the subjects. Here, the rate of wrong response refers to

the total number which is the number of the second hand

walked 2 grids but the subject didn’t press the “Del”

button adds the number of the second hand walked nor-

mally but the subject pressed “Del” button in the propor-

tion of the total number of the second hand walked 2

grids.

The second experimental task is short-term memory.

The earlier research has shown that human short-term

G. J. Zhang et al. / HEALTH 1 (2009) 284-289

286

memory capacity is very limited and its storage time is

short, it was considered as the bottleneck of human in-

formation procession. In this task, 20 groups of alphabet

need the subjects recall one by one, and every group of

alphabet consist of 10 letters, 10 letters showed on the

computer screen in succession at a speed of one letter

every two seconds, when the last letter of one group al-

phabet appeared, there were 10 seconds for the subjects

to write the letters just showed on the computer screen

from their memory, the computer will automatically

compare the letters which the subjects wrote down with

the alphabet, the number of the letters recalled correctly

will be taken as the subjects’ short-term memory per-

formance, and the average number of the 20 groups of

letters recalled correctly will be taken as the data to be

analyzed in the following.

The third experimental task is addition arithmetic. The

computer will display an equation of a pair of three-digit

numbers addition on the screen every time, such equa-

tions in total up to 30, some of them are wrong, and

some are right. The task required the subjects to judge

them whether right or not as quickly and accurately as

possible. Pressing the button “enter” on the low right

keyboard when the equation is right, and pressing the

button “ctrl” on the low left keyboard when the equation

is wrong, the next equation appeared immediately when

the subjects completed pressing key, the computer will

automatically record the judging time and check whether

the judge is right or not, the average judging time and

the correct judging rate for the 30 equations will be ana-

lyzed.

3. RESULTS

3.1. Vigilance Reaction Analysis

The vigilance reaction performance under two kinds of

experimental condition in each period was analyzed by

paired-samples T test, in addition, the vigilance reaction

performance under the same experimental condition in

three periods was analyzed with ANOVA, and the result

is shown in Table 1. The same analysis to short-term

memory, addition arithmetic, and results are shown in

Table 2, Table 3, and Table 4.

Table 1 shows that in three experimental periods, the

subjects who took LTN have significantly higher vigi-

lance than those without LTN, such situation especially

obvious at 14:30-15:30, the napping subjects’ rate of

signals responded wrong is 10% lower than that of not

napping ones, even at 16:30-17:30 and 20:00-21:00, the

rate of signals responded wrong is also 4% lower, which

proves that lunch time napping exert positive effect on

vigilance for people no matter in the afternoon or in the

early evening.

Table 1 also shows that for the LTN subjects, their

vigilance hadn’t changed significantly in the three ex-

perimental periods; however, as for the not having LTN

subjects, their vigilance at 14:30-15:30 is significantly

lower than that at 16:30-17:30 and 20:00-21:00, there

wasn’t significant difference between the second period

and third period.

3.2. Short-term Memory Analysis

Table 2 lists the comparative analysis results of subjects’

short-term memory capacity under two experimental

conditions and in three experimental periods.

It can be seen from Table 2 that only at 14:30-15:30,

the subjects who took LTN have better short-term mem-

ory performance than those without LTN, at 16:30-17:30

and 20:00-21:00, there wasn’t significant difference be-

tween them.

Table 2 shows that, as for the subjects who took LTN,

the significant difference about short-term memory ca-

pacity wasn’t found in three periods, however, as for the

subjects who didn’t take LTN, their short-term memory

performance at 14:30-15:30 is worse than that at

16:30-17:30 and 20:00-21:00, and there wasn’t signifi-

cant difference between 16:30-17:30 and 20:00-21:00.

3.3. Addition Arithmetic Analysis

In order to analyze the effect of LTN on human arithme-

tic calculation performance, this research made the

comparative analysis of calculation speed and calcula-

tion accuracy rate under two different experimental con-

ditions and in three experimental periods, the results

shown in Table 3 and Table 4.

Table 3 lists the comparative analysis results of

arithmetic calculation speed under two experimental

conditions and in three experimental periods.

Table 3 shows that only at 14:30-15:30, the arithmetic

calculation speed of the subjects who took LTN is sig-

nificantly faster than that of those without LTN, while at

16:30-17:30 and 20:00-21:00, the significant difference

wasn’t found between them.

As can be seen from Table 3, for the subjects who

took LTN, their arithmetic calculation speed is almost

the same, but for the subjects who didn’t take LTN, the

arithmetic calculation speed at 14:30-15:30 is signifi-

cantly slower than that at 16:30-17:30 and 20:00-21:00,

and there wasn’t significant difference between

16:30-17:30 and 20:00-21:00.

Table 4 lists the comparative analysis results of the

calculation accuracy rate under two experimental condi-

tions and in three experimental periods.

Table 4 shows that only at 14:30-15:30, the calcula-

tion accuracy rate of subjects who took LTN is signifi-

cantly higher than that of those without LTN, while at

16:30-17:30 and 20:00-21:00, the significant difference

couldn’t be found between them.

As can be seen from Table 4, as for the subjects who

took LTN, their arithmetic calculation accuracy rate is

almost the same, but for the subjects who didn’t take LTN,

G. J. Zhang et al. / HEALTH 1 (2009) 284-289

287

Ta ble 1. Vigilance reaction (the rate of signal responded wrong).

experimental periods

Experimental

condition

the rate of

signal re-

sponded

wrong

14:30-15:30 16:30-17:30 20:00-21:00 F LSD

Mean 0.054

(NVR1)

0.063

(NVR2)

0.060

(NVR3)

Having lunch

time napping Std.dev. 0.044 0.043 0.045

0.309

NVR1≈NVR2

NVR1≈NVR3

NVR2≈NVR3

Mean 0.148

(NNVR1)

0.105

(NNVR2)

0.102

(NNVR3)

Not Having

lunch time nap-

ping Std.dev. 0.060 0.055 0.058

5.948**

NNVR1> NNVR2

NNVR1> NNVR3

NNVR2≈NNVR3

T 20.828** 10.779** 9.069**

Table 2. Short-term memory capacity (the number of letters recalled correctly).

experimental periods

Experimental

condition

Short-term

memory

capacity 14:30-15:30 16:30-17:30 20:00-21:00 F LSD

Mean 8.05

(NSM1)

8.09

(NSM2)

8.01

(NSM3)

Having lunch

time napping Std.dev. 0.340 0.373 0.412

0.383

NSM1≈NSM2

NSM1≈NSM 3

NSM2≈NSM 3

Mean 7.30

(NNSM1)

7.96

(NNSM2)

7.92

(NNSM3)

Not Having

lunch time nap-

ping Std.dev. 0.390 0.582 0.334

20.588**

NNSM1< NNSM2

NNSM1< NNSM3

NNSM2≈NNSM3

T 31.068** 1.145 1.665

Table 3. Arithmetic calculation speed (seconds/one equation).

experimental periods Experimental

condition

arithmetic

calculation

speed 14:30-15:30 16:30-17:30 20:00-21:00 F LSD

Mean 5.06

(NCS1)

5.03

(NCS2)

4.99

(NCS3)

Having lunch

time napping

Std.dev. 0.339 0.338 0.402

0.322

NCS1≈NCS2

NCS1≈NCS3

NCS2≈NCS3

MeNot Having

lunch time nap-

ping

an 5.49

(NNCS1)

5.01

(NNCS2)

5.04

(NNCS3)

Std.dev. 0.402 0.405 0.337

14.980**

NNCS1< NNCS2

NNCS1< NNCS3

NNCS2≈NNCS3

T 15.086** 0.813 1.708

Table 4. The calculation accuracy rate.

experimental periods

Experimental

condition

the calcula-

tion accuracy

rate 14:30-15:30 16:30-17:30 20:00-21:00 F LSD

Mean 0.763

(NCAR1)

0.762

(NCAR2)

0.766

(NCAR3)

Having lunch

time napping Std.dev. 0.041 0.042 0.040

0.058

NCAR1≈NCAR2

NCAR1≈NCAR3

NCAR2≈NCAR3

Mean 0.701

(NNCAR1)

0.756

(NNCAR2)

0.752

(NNCAR3)

Not Having

lunch time nap-

ping Std.dev. 0.763 0.072 0.075

5.272**

NNCAR1< NNCAR2

NNCAR1< NNCAR3

NNCAR2≈NNCAR3

T 7.423** 0.670 1.391

the arithmetic calculation accuracy rate at 14:30-15:30

is significantly lower than that at 16:30-17:30 and

20:00-21:00, and there wasn’t significant difference be-

tween 16:30-17:30 and 20:00-21:00.

4. DISCUSSION

4.1. Conclusions

This research showed that as for the subjects who didn’t

take LTN, their mental work performance at 14:30-15:30

is significantly worse than that at 16:30-17:30 and

20:00-21:00, while as for those who took LTN, their

mental work performance almost is the same in three

experimental periods, which indicated that midafternoon

nap zone as Hayashi et al. [10], Broughton mentioned

exists objectively for habitual nappers [11], this experi-

ment provided the direct evidence for their standpoint.

This research also showed that the subjects who took

LTN have significantly better mental work performance

than those without LTN at 14:30-15:30, which proved

that LTN could overcome habitual nappers’ “midafter-

noon nap zone”.

It is interesting that as for mental work performance

of such task as short-term memory and arithmetic calcu-

lation, there wasn’t significant difference between the

G. J. Zhang et al. / HEALTH 1 (2009) 284-289

288

subjects who took LTN and those who didn’t take it at

16:30-17:30 and 20:00-21:00, however, as for vigilance

reaction, the subjects who took LTN have significantly

better performance than those who didn’t take it at the

periods as above, which may be caused by the different

nature of the experimental tasks. In specification, the

experimental task of vigilance reaction is relatively bald,

such tasks may easily induce the subjects who didn’t

take LTN to desire sleep, and the result is that their per-

formance is worse than the subjects who took LTN. Ha-

yashi et al. also took for that nap could reduce human

sleepiness and enhance vigilance [7,8,12]. However, as

for short-term memory and arithmetic calculation, these

tasks’ mental workload are relatively overload, the sub-

jects who didn’t take LTN weren’t easily to stimulate

sleepiness, and the result is that their performance are

the same as those who took LTN. Hayashi et al. have

also gotten such conclusion [7]. This research results

indicated that the effect of LTN on habitual nappers’

mental work performance is moderated by the nature of

mental work at 16:30-17:30 and 20:00-21:00.

It is worth noting that this research didn’t deny the

existence of sleep inertia. Hayashi et al. hold that sleep

inertia is inevitable [7], and Taub [13], Dinges et al. be-

lieved that sleep inertia may last 15-35 minutes [14]. In

this study, the measurement of mental work performance

is carried out 30 minutes after LTN, as for the subjects

who took LTN, their mental work performance has not

changed significantly, which provides indirect evidence

for that sleep inertia may last 15-35 minutes, because if

sleep inertial exceeds 30 minutes, the mental work per-

formance of the subjects who took LTN at 14:30-15:30

should be lower than that at 16:30-17:30 and 20:00-21:00,

but this experiment result wasn’t the case.

It should be noted that the above conclusions are got

with the subjects who have LTN habit and took normal

sleep at night and 1 hour and a half naps at noon, if ex-

perimental context was not the case, the conclusion of

this study may be different, many scholars believed that

the effects of naps depend on the duration of prior wake-

fulness, the time of day of the nap, and its duration

[15,16].

Many people feel that they are sleepy and work ineffi-

ciently in the afternoon and evening without LTN; how-

ever as for the complex and over-workload task, such as

short-term memory and arithmetic calculation, the con-

clusion of this study is contradict with it, it doesn’t mat-

ter whether to take LTN or not, human work perform-

ance of such complex task at 16:30-17:30 and 20:00-21:00

is the same, the reason may due to the difference be-

tween experiment and reality. In the experiment, sub-

jects’ attention is highly focused, the pace of task is rela-

tively fast, the experiment duration is short (each period

about 1 hour), and also strong incentive provided. In

reality, the pace of many tasks is slow, and the work du-

ration is long, which easily induce people to be relaxed

and stimulate sleepiness. Despite some difference be-

tween experimental context and reality, we think that

this experiment proved that at least in theory, for com-

plex and over-workload mental work, LTN is a phe-

nomenon to be overcome temporarily in the later after-

noon and in the early evening (16:30-17:30 and

20:00-21:00), not having LTN didn’t exert significant

negative effect to the performance of such task.

4.2. Recommendations

As for habitual nappers, because of LTN can ease such

physical embarrassment as mid-afternoon nap zone,

therefore, LTN is needed if conditions allow, especially

for those whose home is near to their work site. For the

task of vigilance reaction, LTN is particularly important

because LTN can improve its performance in the after-

noon and evening.

Whether having LTN or not has great influence on

habitual nappers’ mental work efficiency at 14:30-15:30

in order to eliminate the negative influence, on one

hand, the government departments should try to avoid

arranging important mental activities at this period of

time, such as examinations, and so on. Unfortunately,

Chinese government departments doesn’t seem to no-

tice it, for example, the most important college en-

trance examination, its examination time in the after-

noon was always from 14:00 to17:00, as for some

students who did not take LTN, their test score are

likely to be lower than their real achievements, which

is unfair for them to compete with students who have

comfort LTN condition. On the other hand, many

Chinese enterprises should adjust their shiftwork

schedule, that is changing the present shiftwork time-

table (8:00-16:00, 16:00-24:00, 24:00 -8:00) into the

new one (6:00-14:00, 14:00-22:00, 22;00-6:00), which

can let habitual nappers avoid not had HLT on duty

yet at 14:30-15:30.

4.3. Limitations and Future Directions

All the subjects participated in this experiment have

LTN habit, although it consists of the Chinese work and

rest mode, we can’t find out the effect of LTN on mental

work efficiency of those who haven’t LTN habit, there is

no doubt that to study it is an interesting work, for ex-

ample, if we find that LTN has no significant effect on

mental work efficiency of those who haven’t LTN habit,

in addition, changing the LTN habit doesn’t bring sig-

nificant bad physical influence, then to reform Chinese

public sectors’ work and rest timetable is go without

saying, because the timetable (9:00 -17:00) in many pri-

vate sector is more reasonable than the timetable (8:00

-12:00 and 14:00-17:30) in public sectors obviously,

which keeps the continuity of eight hours work a day

and not require the public to wait out of the government

G. J. Zhang et al. / HEALTH 1 (2009) 284-289

289

office at 12:00-14:00. [8] Hashi, M., Makiko, W. and Hori, T. (1999) The effects of

a 20 min nap in the mid-afternoon on mood, performance

and EEG activity. Clini cal Neurophysiology., 110,

272–279.

5. ACKNOWLEDGMENT

[9] Driskell, J.E. and Mullen, B. (2005) The efficacy of naps

as a fatigue countermeasure: a meta-analytic integration.

Human Factors., 2, 360-377.

This study was supported by the Science and Technology Research

Project of Hubei province under Grant B20080402, and also was sup-

ported by the Humanity Social Science Foundation of Hubei province

under Grant 2008y054. [10] Hayashi, M., Morikawa, T. and Hori, T. (2002) Cir-

casemidian 12-hour cycle of slow wave sleep under con-

stant darkness. Clinical Neurophysiology., 113,

1505-1516.

REFERENCES [11] Broughton, R.J. (1998) SCN controlled circadian arousal

and afternoon “nap zone”. Sleep Research Online., 1,

166-178.

[1] Liao, J.Q. (1996) The effects of napping on human per-

formance of vigilance. Ergonomics., 4, 29-32. [12] Hayashi, M., Fukushima, H. and Hori, T. (2003) The

effects of short daytime naps for five consecutive days.

Sleep Research Online., 5, 13–17.

[2] Macchi, M.M., Boulos, Z., Ranney, T., Simmons, L. and

Campbell, S.S. (2002) Effects of an afternoon nap on

nighttime alertness and performance in long-haul drivers.

Accident Analysis and Prevention., 34, 825-834. [13] Taub, J.M. (1979) Effects of habitual variations in nap-

ping on psychomotor performance, memory, and subjec-

tive states. International Journal of Neuroscience., 9,

97-112.

[3] McEvoy, R.D. and Lack, L.L. (2006) Medical staff work-

ing the night shift: can naps help? Medical Journal of

Australia., 7, 349-350. [14] Dinges, D.F., Orne, E.C., Evans, F.J. and Orne, M.T.

(1981) Performance after naps in sleep-conductive and

altering environments. In Johnson, L.C., Tepas, D.I.,

Colquhon, W.P. & Colligan, M.J. (Eds.), Biological

Rhythms, Sleep and Shift Work. S. P. Medical and Scien-

tific Books., New York, 539-552.

[4] Mednick, S.C., Nakayama, K. and Cantero, J.L., et al.

(2002) The restorative effect of naps on perceptual dete-

rioration. Nature Neuroscience., 7, 676-680.

[5] Backhaus, J. and Junghanns, K. (2006) Daytime naps

improve procedural motor memory. Sleep Medicine.,

7,508–512. [15] Lumley, M., Roehns, T., Zorick, F., Lamphere, J. and

Roth, T. (1986) the alerting effects of naps in

sleep-deprived subjects. Psychophysiology., 23, 403-408.

[6] Milner, C.E., Fogel, S.M. and Cote, K.A. (2006) Habitual

napping moderates motor performance improvements

following a short daytime nap. Biological Psychology.,

73, 141–156. [16] Naitoh, P

. (1981) Circadian cycles and restorative power

of naps. In Johnson, L.C., Tepas, D.I., Colquhon, W.P. &

Colligan, M.J. (Eds.), Biological Rhythms, Sleep and

Shift Work. S. P. Medical and Scientific Books., New

York, 553-580.

[7] Hayashi, M., Ito, S. and Hori, T. (1999) The effects of a

20-min nap at noon on sleepiness, performance and EEG

activity. International Journal of Psychophysiology., 32,

173-180.

Openly accessible at