Psychology
2011. Vol.2, No.7, 674-680
Copyright © 2011 SciRes. DOI:10.4236/psych.2011.27103
Effects of Video Game Playing on the Circadian Typology and
Mental Health of Young Czech and Japanese Children
Milada Krejci1, Kai Wada1,2, Miyo Nakade3, Hitomi Takeuchi3, Teruki Noji4, Tetsuo Harada2
1Department of Health Education, Faculty of Education, University of South Bohemia,
Jeronymova, Ceske Budejovice, Czech Republic;
2Laboratory of Environmental Physiology, Graduate School of Integrated Sciences of Human and Nature,
Kochi University, Akebonocho, Kochi, Japan;
3Department of Foods and Nutrition, Tokai-Gakuen University, Nagoya, Aichi, Japan;
4Department of Physical Education, Faculty of Education, Kochi University, Kochi, Japan.
Received May 9th, 2011; revised July 27th, 2011; accepted September 2nd, 2011.
The objective of this study is to examine the effects of video game playing on sleep-wake cycles and mental
health of young Czech and Japan children. A cross-sectional survey with 497 Czech children (240 girls, 257
boys; mean age of 4.60 years; 49˚ - 51˚N) and 599 Japanese children (314 girls, 285 boys: 3.79 years; 33˚N)
from 20 kindergartens and nursery schools. 20% and 30% of Czech and Japanese children had their own video
game devices. Young children who played video games every day had later sleep and wake times (P < 0 .001)
and were more evening-typed (P < 0.001) than those who did not every day in the both countries. The longer
Czech children played video games per time, the later sleep and wake times were (P < 0.001). Czech children
who played video games from 18:00 - 21:00 showed later sleep times and shorter sleep hours (P < 0.001) on
weekdays than those who played at earlier times. Japanese children who played video games from 18:00 - 21:00
were more evening-typed and woke up later than those who played at earlier times (P < 0.001). Czech children
who had their own video game devices had a higher frequency of anger than those who did not (P < 0.001). Ha-
bitual video game playing in the evening may make children more evening-typed and it may also be speculated
to make them more aggressive in both countries.
Keywords: Chronotype, Video Game Playing, Circadian Typology, Mental Health
Introduction
Issues concerning diurnal rhythms and sleep health are im-
portant to health professionals, school teachers, parents and the
children themselves. Video games have become one of the
major playing tools for children all over the world. Many epi-
demiological studies have been done on the relationship of
video game playing with sleep health and physical health of
primary and secondary school children, mainly aged 6 - 15 yrs.
Video-game use more than 1h by 6 - 12 yrs and more than 2
h by junior high students were reported to promote black rings
under the eyes (BR) and muscle stiffness in the shoulder (MS)
(Tazawa & Okada, 2001) and longer sleep onset latency (Ka-
gamimori, 2006), respectively. In Singapore, a questionnaire
study on children aged 6 - 12 yrs showed that total sleep time
(TST) was reduced by playing computer games after 20:00
(BaHammam et al., 2006). An epidemiological study on Ger-
man primary school children revealed that 11% of them played
computer games more than 3 hours daily and went to bed after
21:00 (Gaina et al., 2007), and another study on German chil-
dren aged 5 - 11 yrs showed that viewing TV or playing video
games before sleep was associated with sleep and behavior
problems (Wiater et al., 2008). A questionnaire study on Bel-
gium adolescents showed that those who played more time
computer games went to bed later and woke up later (Van Den
Bulck, 2004). A postal inquiry study on Finns aged 12 - 18 yrs
substantiated the mediating hypothesis that intensive ICT (In-
formation Communication Technology) was associated with
poor sleep health and increased waking-time tiredness (Puna-
maki et al., 2007). Yokomaku et al. (2008) reported that eve-
ning-typed infants aged 4 - 6 yrs showed more several prob-
lematic behaviors than non-evening-typed ones.
Some experimental interference studies have been done so
far on the effects of computer game playing. Playing the game
prolonged sleep latency in Japanese adult males (Higuchi et al.,
2005). Dworak et al. (2007) reported that playing game reduced
slow-wave-sleep, declined verbal memory performance, pro-
longed sleep-onset latency and increased stage 2 sleep on
school-aged German children. Smyth (2007) also reported that
the TV game playing decreased sleep quality in 18 - 20 yrs olds
students. However no experimental studies have been done on
video game effects upon the aspects of mental health. Light
exposure from a fluorescent lamp promotes an evening-type
life-style, and elementary school students were more sensitive
to light than University students (Harada & Takeuchi, 2001;
Harada, 2008). Light emitting from a computer game display is
predicted to delay the circadian phase of young children which
may be more sensitive to light rather than elementary school
students.
Exposure to strong blue lights from the displays of video
game devices during the first half of subjective night may de-
press the plasma melatonin level of Japanese junior high school
students (Harada, 2004) as well as cause a delay in the phase of
the human circadian clock (Honma & Honma, 1988). Ac-
cording to an epidemiological study on 5th grade students aged
10 - 11 yrs attending elementary schools all over the Japan,
92% of such students had their own video game device in 2007
(Japan Parents and Teachers Association, 2007). Playing video
games occupies a great amount of free time and psychological
space in children. Video game playing has been hypothesized to

M. KREJCI ET AL. 675
reduce the blood flow and disturb electro-physiological active-
ties in the frontal lobe of the cerebral cortex (Mori, 2002).
Lights emitted from the displays of video games may stimulate
the SCN (suprachiasmatic nucleus) which is thought to be the
controlling center of the circadian system Herman (Herman,
2008).
However, there have been no integrated studies conducted on
the effects of video game playing on circadian typology, sleep
habits and mental health of children aged 2 - 6 yrs when the
fundamental physiological systems governed by the circadian
clock systems are developing. In this study, the effects of video
game playing on the young children are hypothesized to be
much higher than the effects on high school and University
students. This might be because the daytime serotonin level in
the brain and nighttime plasma melatonin level are much higher
in 3 - 8 year olds than in older children, and the amount of sup-
pression of plasma melatonin promoted by light from fluores-
cent lamp is also expected to be higher in younger children
(Harada, 2004; Waldhauser et al., 1988).
This study aims at examining the effects of video game
playing on sleep-wake cycles based on circadian typology and
mental health of children aged 2 - 6 years living in “morning-
typed” (Czech) and “evening-typed” (Japan) societies (Wada et
al., 2009) from an epidemiological point of view.
Participants and Methods
Study Site
The study was conducted in 20 public kindergartens and
nursery schools, distributed all over the Czech Republic (49˚ -
51˚N) (mainly South-Bohemia region) located in central Europe,
and distributed in Kochi City (33˚N) in Kochi Prefecture facing
the Pacific Ocean in the southern half of Shikoku Island in
Japan. The Czech Republic and Japan are typical “morn-
ing-typed” and “evening-typed” societies, respectively. For
example, the first class in the morning at Czech and Japanese
Universities starts at 8:00 and 8:50, respectively. Similarly,
Czech and Japanese kindergartens start at 6:30 - 8:00 and 8:30 -
9:30, respectively. Most official bus and train services start at
4:00 - 5:00 in the Czech Republic and 5:00 - 6:00 in Japan.
Czech laborers in factories start work at 6:00 in the Czech Re-
public, whereas Japanese laborers start at 8:00 - 9:00. Many
Czech and Japanese official services open at 7:30 - 8:00 and
9:00, respectively. On the other hand, Czech labors stop to
work earlier than Japanese ones. The official working hours of
public employees per day is legislated to be 8.5 hours in Czech
and 8 hours in Japan (Czech: 8:00 - 17:00 or 7:30 - 16:30, Ja-
pan: 8:30 - 17:30 including 0.5 h (Czech) and 1 h (Japan) of
lunch break in many cases). Young Czech children are expected
to use video games in earlier hours of the evening than young
Japanese children. As a result, smaller effects of using video
games can be expected in young Czech children than in young
Japanese children.
Participants
As kindergarten staffs have more free-time to be spent for the
management of the questionnaire work in the spring than in the
fall in the Czech Republic and vice versa in Japan, participation
in fall was recommended by kindergartens in the Czech Repub-
lic and in spring for Japan. Among randomly selected children
attending one of 11 kindergartens (for children aged 2 - 6), 497
children (response rate: 86%; 240 girls, 257 boys; 2y: 15; 3y:
77; 4y: 110; 5y: 184; 6y: 111; mean ± SD: 4.60 ± 1.09y) par-
ticipated in this study from the Czech Republic. Japanese 599
children among those for whom we asked to answer the ques-
tionnaire, participated in (response rate: 70%; 314 girls, 285
boys: 2y: 100, 3y: 153, 4y: 149, 5y: 165, 6y: 32; mean ± SD:
3.79 ± 1.17y). The participants attended one of 1 kindergarten
(for children aged 4 - 6) and 9 nursery schools (for babies and
children aged 0 - 6) governed by Kochi City in Kochi Prefec-
ture of Japan (33˚N). These 9 nursery schools were also ran-
domly selected from all 25 nursery schools governed by Kochi
city. Babies and young children aged 0 - 1 were excluded from
the study because of flexible sleep-wake cycles.
Questionnaire
To measure diurnal preference of the young children, a
Japanese and Czech version for children (Harada et al., 2007)
of MEQ originally constructed by Torsvall and Åkerstedt (1980)
was administrated. This MEQ consisted of seven questions:
three pertaining to sleep offset timing in the morning, one to the
peak timing of activity during the daytime and three to sleep
onset timing in the evening, which of young children was
judged due to the observation in holidays by mostly their
mothers (>95%). Answer can be selected from 4 alternatives in
each question, and the total of 7 answers can range from 7 (ex-
tremely evening-typed) to 28 (extremely morning-typed).
Czech and Japanese versions of an integrated questionnaire
(34 questions for children and 11 questions for their parents)
which consisted of a morningness-eveningness (M-E) ques-
tionnaire (MEQ) originally constructed by Torsvall and Åker-
stedt (1980) and an original questionnaire on sleep habits (Ha-
rada et al., 1988), video game playing and mental health and
were completed in June or November 2007 to avoid the severe
summer and winter seasons.
A Japanese version of the integrated questionnaire has been
used in several studies (Harada, 2008; Harada et al., 2007; Ha-
rada et al., 2006). An English version (Harada et al., 1998) of a
questionnaire which includes most of the integrated question-
naire was translated to Czech by Krejci (author). The English
version of a questionnaire about video games that Harada (au-
thor) constructed was translated to Czech and Japanese by Kre-
jci and Harada. Lastly, a detailed discussion, check and revision
were made by four academic members (including one author:
Krejci) of the Department of Health Education, Faculty of
Education, University of South Bohemia, and two Japanese
authors (Harada and Wada) on the integrated questionnaire to
ensure that both translations were as similar as possible.
Statistical Analysis of Questionnaire Data
The questionnaire was distributed to all or some of the chil-
dren attending randomly selected kindergartens or nursery
schools. Parents (95% or more of which were mothers) an-
swered the questionnaire for themselves (MEQ: 7 items, play-
ing video games: 4 items) and also for their children (MEQ: 7
items, playing video games: 4 items, sleep habits: 11 items,
meals: 8 items, mental health: 2 items, exposure to sunlight: 3
items). Fundamental comparisons on MEQ, sleep habits and
mental health were performed between Czech and Japanese
children (Table 1). Data was statistically analyzed with SPSS
software (12.0 J for Windows; SPSS Inc., Chicago, IL, USA).
Ethical Treatment
The study followed the updated guidelines established by
Chronobiology International for the conduct of research on

M. KREJCI ET AL. 676
Table 1.
Comparison of circadian typology and sleep habits between Czech and
Japanese children and their parents (mothers).
Mean ± SD or % (total N‡)
Czech Japan P-value
Circadian typology
ME scores#
Parents 9.6 ± 3.3(604) 20.0 ± 3.2(682) 0.025*
(Median:20) (20)
Children 22.1 ± 3.1(626)20.39 ± 3.6(626) <0.001*
(Median:22) (20)
Sleep habits of children
Bed time (h)
Weekday 20.1 ± 0.6(634)21.5 ± 0.9(690) <0.001*
Weekend 20.8 ± 0.8(628)21.8 ± 1.0(700) <0.001*
Wake up time (h)
Weekday 6.7 ± 0.3(630) 7.0 ± 0.6(702) <0.001*
Weekend 7.4 ± 0.8(628) 7.5 ± 0.9(698) <0.001*
Sleep latency (min)
Weekday 17.1 ± 10.7(634)21.0 ± 14.1(701) <0.001*
Weekend 15.2 ± 11.0(624)18.7 ± 13.9(698) <0.001*
Sleep hours
Weekday 10.6 ± 0.7(624)9.5 ± 0.8(689) <0.001*
Weekend 10.6 ± 0.9(626)9.7 ± 0.9(695) <0.001*
Difference between weekday and weekend in sleep habits of children
Bed time (h) 0.7 ± 0.6(622) 0.3 ± 0.8(688) <0.001*
Wake up time (h) 0.7 ± 0.7(628) 0.5 ± 0.7(697) 0.033*
Sleep hours (h) –0.01 ± 0.8(620)0.2 ± 1.1(682) <0.001*
Mental health
% Frequent “often”
Anger 1.3 (633) 9.3(678)†
Depression 12.6(626) 0.7(676) <0.001†
Note: *Mann-Whitney U-test, †χ2 test, ‡Totals vary as some respondents have not
answered the questions. #after Wada et al.
human subjects (Portaluppi et al., 2010). The concepts and
purpose of the study were carefully explained in writing and
orally to kindergarten or nursery teachers and the parents of the
children were told that questionnaires would be conducted in a
completely unregistered manner and answers would be used
only for academic purposes. After the explanation, all parents
agreed to participate in the questionnaire study, which was
administered at home.
Results
International comparisons in Table 1 include circadian ty-
pology, sleep habits and mental health. Czech children were
more morning-typed and showed better sleep quality and quan-
tity than Japanese children. However, there was larger phase-
delay at bedtime in weekend in Czech children than in Japanese
children. A larger number of Czech children than Japanese
children felt “depressed”, while the reverse was true for chil-
dren who felt “anger”.
30.8% (females: 61 of 236, 25.8%; males: 90 of 254, 35.4%)
and 27.1% (females: 74 of 306, 24.2%; males: 84 of 278,
30.2%) of Czech and Japanese children aged 2 - 6 yrs played
video games, (“players”) respectively (Table 2). Players
showed lower M-E scores (more evening-typed), later bedtime
and wake-up time than non-players in Japanese children. In
Czech children, players showed lower M-E scores (more eve-
ning-typed) than non-players. Few children aged 2 - 3 yrs
played video games, and 25.7% and 31.9% of 4 year old chil-
dren played video games in the Czech Republic and Japan,
respecttively (Table 2). Japanese children who played video
games every day showed significantly lower Morningness-
Eveningness scores (more evening-typed) than those who did
not play at all (Mann-Whitney U-test: z = –2.391, P = 0.017 )
(Table 3(a)). Czech children who played video games every day
tended to go to bed 30 minutes later than those who played 0 -
1 times per week (Table 3(a)). Czech children who played
video games more than 0.5 hours per time showed significant
later bed times than those who played 0 - 0.5 hours (Table 3(b))
(Mann-Whitney U-test: z = –2.174, P = 0.030). 79.2% of Czech
children who played video games did so from 15:00 to 18:00,
whereas 63.4% of the Japanese children who played video
games did so from 18:00 to 21:00. Both times of day corre-
spond with sunset times of the study season. Czech children
who played video games from 15:00 to 18:00 went to bed sig-
nificantly later on weekdays than those who played at earlier
times (Mann-Whitney U-test: z = –2.357, P < 0.018) (Table
3(c)). Japanese children who played video games from 18:00 to
21:00 were significantly more evening-typed and woke up on
average 20 minutes later in the morning than those who played
at earlier times (Table 3(c)). The correlation value (r-value)
between the morningness-eveningness (M-E) scores of children
and mothers was relatively low (r = 0.320) in Czech partici-
pants, whereas it was relatively high (r = 0.422) in Japanese
participants.
Condition of mental health in Czech and Japanese infants
was shown in Table 1. The higher the frequency of playing
video games was per week, the lower the frequency of depress-
sion was only for Japanese children (χ2-test, Czech: χ2-value =
5.830, df = 9, P = 0.757; Japan: χ2-value = 14.169, df = 6, P =
0.028). Instead, Japanese children who played video games
tended to feel anger with significantly higher frequency than
those who did not do so (χ2-test, Czech: χ2-value = 6.190, df = 1,
P = 0.241; Japan: χ2-value = 6.120, df = 1, P = 0.013) (Figure 1).
Discussion
Several factors could affect the circadian typology in adoles-
cents and elder students: for example earlier sunrise leading to
morning-typology (Randler, 2008: on adolescents); females
with more advanced sleep phase than males (Tonetti et al., 2008:
on 13 - 25 yrs students). Evening-typology could relate to lower
mental health (Hirata et al., 2007: on 19 - 30 students; Harada,
2008: on 2 - 25 yrs) and higher scores of CBCL (Children Be-
havior Checklist/4 - 8 to detect several problematic behaviors)
(Yokomaku, 2008: on 4 - 6 yrs children).
Habitual playing of video games might also affect the cir-
cadian typology of both Japanese and Czech young children

M. KREJCI ET AL. 677
Table 2.
Fundamental data on video game playing by Czech and Japanese children aged 0 - 6 yrs in 2007.
Males Does your child use a video game device?
Czech Japan
Age
0 1 2 3 4 5 6 0 1 2 3 4 5 6
“Yes” 0 0 1 4 15 40 30 0 0 4 7 29 34 10
(%) (0) (0) (16.7) (11.1) (28.3) (41.7) (47.6) (0)(0)(8.0) (10.9) (42.0) (42.5) (66.7)
“No” 0 6 5 32 38 56 33 14 36 46 57 40 46 5
Total 0 6 6 36 53 96 63 14 36 50 64 69 80 15
Females Does your child use a video game device?
Czech Japan
Age
0 1 2 3 4 5 6 0 1 2 3 4 5 6
“Yes” 0 0 0 4 13 27 17 0 0 6 13 17 30 8
(%) (0) (0) (0) (10.3) (23.1) (31.4) (37.0) (0)(0)(12.8) (15.3) (22.7) (36.1) (50.0)
“No” 1 15 9 35 43 59 29 8 34 41 72 58 53 8
Total 1 15 9 39 56 86 46 8 34 47 85 75 83 16
(playing games leading to evening-type) and reduce sleep
health like as the video game playing in the elder children (Ka-
gamimori, 2006; BaHammam et al., 2006; Gaina et al., 2007;
Wiater et al., 2008; Van Den Bulck, 2004; Punamaki, et al.,
2007). This study shows that it is common for Japanese chil-
dren to play video games in the evening from 18:00 to 21:00
which is around sunset and includes “dusk” in June in Kochi.
Exposure to lights from the displays of video game devices,
while playing video games in the evening could be hypothe-
sized to have phase-delaying effects on the circadian clock. It is
because the exposure to lights during 19:00 ~ 24:00 could cause
a delay in the phase of children’s circadian clocks (Honma &
Honma, 1988; Harada, 2004) and might reduce the plasma
melatonin level as a “sleep onset agent” in the evening (Zhda-
nova et al., 1995; Harada, 2004). Japanese mothers could be
more likely to synchronize their own diurnal rhythms to their
children than Czech mothers. Strong discipline to prevent the
use of video games after sunset might be critical, especially for
Japanese children.
On the other hand, Czech children tended to play video
games mainly from 15:00 to 18:00, which is earlier than the
first half of subjective night, is around sunset and also includes
“dusk” in November at Ceske Budejovice (49˚N). Playing
video games around sunset may still cause a backward shift in
both sleep and wake times, although it is much earlier than the
first half of subjective night (around 18:00 ~ 24:00). Honma
and Honma (1988) reported that exposure to bright lights from
fluorescent lamps from 20:00 to 02:00 caused a delay in the
phase of the circadian clock (which controls rhythms such as
body temperature rhythms) of adult subjects. In the case of
children, exposure to the lights from displays of video game
devices even late in the afternoon might relate to the circadian
clock phase and plasma melatonin level.
Positive associations between evening-type preference and
depressive mood have been previously described in adults
(Drennan et al., 1991; Chelminski et al., 1999) and adolescents
(Giannotti and Cortesi, 2002; Takeuchi et al., 2002; Harada,
2008; Hirata et al., 2007). Several reports also have shown that
de-synchronization of the circadian clock system and the social
time schedule was often accompanied by a depressed mood
(Harada, 2008). The current research showed that children aged
2 - 6 yrs in Japan also exhibited strong positive associations
between evening-type preference and aggressive mental con-
dition (anger and irritation) (Harada, 2008; Hirata et al., 2007).
Playing video games in the evening or late afternoon might
relate to higher levels of aggression as anger and irritation indi-
rectly via the de-synchronization of the circadian clock or by
directly affecting children’s brains.
One limitation in this study that should be mentioned is that
there was no investigation regarding the content of the video
games. Recently, for example, Wei (2007) reported that playing
violent video games on the Internet was associated with greater
tolerance of violence, a lower empathetic attitude and more
aggressive behavior in Chinese adolescents. A higher level of
aggression shown by children who play video games in the
evening or afternoon could be partially caused by more violent
and frustrating content. Effects of video game content on men-
tal health in children remain a question to be solved. Another
shortcoming is the lack of correspondence in the sampling sea-
son. Spring data on the Czech Republic side and fall data on the
Japanese side should be collected in the near future, although
support from the nursery school staff would be hard to be ob-
tained due to busyness in those seasons in the respective coun-
tries.
Acknowledgements
W
e would like to thank all the members of the kindergartens

M. KREJCI ET AL. 678
Table 3.
(a) Relationship between freq u en c y o f p l a yi n g v i de o ga mes, M-E scores and slee p ha bi ts (M: Mean, SD: Standard deviation) (number of c hi l d r e n); (b)
Relationship between duration of playing video games per once and M-E scores and sleep habits (M: Mean, SD: Standard deviation) (number of
children); (c) Relationship between time of day to play video games and M-E scores and sleep habits (M: Mean, SD: Standard deviation) (number of
children).
(a)
ME scores Sleep time Wakeup time Length of Sleep
Japan Czech Japan Czech Japan Czech Japan Czech
M SD M SD M SD M SD MSD MSD M SD M SD
Everyday 17.42 3.63(19) 20.26 3.25(27) 21.920.7(24)20.53 0.54(30) 7.34 0.56(24) 6.74 0.51(29) 9.42 0.64(24) 10.20 0.63(29)
4 - 5 times 18.82 3.4(17) 20.93 3.45(29) 21.760.6(18)20.330.59(30)7.390.48(19)6.750.38(30) 9.62 0.59(18) 10.410.63(30)
(per week)
2 - 3 times 18.57 3.06(47) 21.69 3.28(77) 21.61 1.06(51) 20.11 0.69(82) 7.13 0.47(51) 6.67 0.53(82) 9.52 0.94(51) 10.56 0.87(82)
0 - 1 times 19.94 3.37(54) 21.88 2.94(56) 21.59 0.62(64) 20.06 0.57(63) 7.15 0.67(64) 6.61 0.41(61) 9.55 0.71(64) 10.54 0.64(61)
Kruskal-Wallis test, P-value:
0.01587 0.09049 0.21462 0.00189 0.05656 0.15441 0.47701 0.12422
Two-way ANOVA, P-value:
Effect of
frequency to play: 0.003 0.003 0.065 0.242
Effect of
Czech-Japan: <0.001 <0.001 <0.001 <0.001
(b)
ME scores Sleep time Wakeup time Length of Sleep
Japan Czech Japan Czech Japan Czech Japan Czech
M SD M SD M SD M SD M SD M SD M SD M SD
0 - 30 mins 18.97 3.52(73) 21.86 3.08(88) 21.64 0.66(83) 20.08 0.59(96) 7.22 0.64(83)6.620.43(95) 9.58 0.65(83) 10.530.67(95)
30 mins - 1 h 19.10 3.24(42) 21.23 2.96(65) 21.62 1.01(50) 20.22 0.54(73) 7.09 0.52(51)6.680.52(72) 9.46 0.99(50) 10.460.63(72)
1 - 1.5 h 18.13 3.1(16) 21.172.78(24) 21.83 0.73(18)20.380.47(24)7.400.43(18)6.750.35(23) 9.57 0.65(18) 10.380.62(23)
1.5 – 2 h 21.00 -(1) 19.173.49(6) 21.50(1) - 20.331.78(6) 7.00(1)- 6.710.68(6) 9.5(1) - 10.38 2.32(6)
2-2.5 h - -
20.40 5.27(5 - - 20.60 1.08(5)- - 7.23 0.48(5) - - 10.63 1.12(5)
2.5 - 3 h 18.33 3.51(3) - -
22.17 1.26(3)- - 7.33 0.58(3)- - 9.17 0.76(3) - -
>3 h - - 20.00(1) - - - 21.00(1) - - - 7.00(1)- - - 0.00(1)-
Kruskal-Wallis test, P-value:
0.672 0.236 0.695 0.030 0.083 0.072 0.290 0.241
Two-way ANOVA, P-value:
Effect of
frequency to play: 0.868 0.217 0.112 0.849
(c)
ME scores Sleep time Wakeup time Length of Sleep
Japan Czech Japan Czech Japan Czech Japan Czech
M SD M SD M SD M SD M SD M SD M SD M SD
06:00 ~ 09:00 19.20 3.9(5) - - 21.65 0.49(5)19.75(1)- 7.200.27(5)6.00(1)- 9.55 0.27(5) 10.25(1)-
09:00 - 12:00 21.50 0.71(2) 19.00(1) - 21.00 0(3)17.00(1- 6.830.29(3)8.00(1)- 9.83 0.29(3) 15.00(1)-
12:00 - 15:00 21.00 1.41(2) 21.46 2.73(13) 21.17 0.24(2)20.13 0.53(14)6.580.12(2)6.930.36(14) 9.42 0.12(2) 10.80 0.48(14)
15:00 - 18:00 20.23 3.05(30) 21.58 2.95(141) 21.67 0.62(37)20.16 0.58(152)7.040.48(38) 6.64 0.46(150) 9.36 0.60(37) 10.47 0.67(150)
18:00 - 21:00 18.46 3.38(71) 20.05 3.773(22) 21.68 0.94(79)20.570.69(24)7.320.63(79)6.820.50(24) 9.64 0.92(79) 10.240.80(24)
21:00 - 24:00 18.33 4.95(2) - - 22.25 0.35(2)- - 7.330.47(2)- - 9.08 0.12(2) - -
03:00 - 06:00 - - 20.00(1) - 20.50(1)7.50(1)- - 11.00(1)- - - - - - -
Kruskal-Wallis test, P-value:
0.024 0.238 0.167 0.014 0.021 0.021 0.239 0.035
Two-way ANOVA, P-value:
Effect of
time-of-day to play <0.001 <0.001 <0.001 <0.001

M. KREJCI ET AL. 679
NO
YES
often sometimes occasionaly never
0% 20% 40% 60% 80% 100%
(a)
YES
NO
often sometimes occasionaly never
0% 20% 40% 60% 80% 100%
(b)
Figure 1.
Relationship between whethe r J ap anese (a) and Czech (b) infan ts pl ay t h e ga m es o n d is pl a y or not and the frequency to b e a ng ry .
who cooperated with this survey. This study was performed as
an official international research project based on The Official
Academic Exchanging Agreement between South Bohemia
University and Kochi University.
Thanks would be sincerely and also due to Foundation for
several financial supports from Research Promotion by Dean of
Faculty of Education, Kochi University (2008-2009), Founda-
tion for the Promotion of International Exchanging Programs
(2008-2009), Kochi University, Foundation for The Kochi
University President’s Discretionary Foundation (2009-2011)
and JSPS Foundation to T. Harada (Project No. 22370089:
2010-2013). Thanks are also due to Mis Laura Sato for her
careful and kind linguistic-editorial work on this paper before
the submission.
References
BaHammam, A., BinSaeed, A., Al-Faris, E., & Shaikh, S. (2006). Sleep
duration and its correlates in a sample of Saudi elementary school
children. Singapore Medicine Journal, 47, 875-881.
Chelminski, I., Ferraro, F. R., Petros, T., & Plaud, J. J. (1999). An
analysis of the evening-morningness imension in “depressive” col-
lege students. Journal of Affective Disorders, 52, 19-29.
doi:10.1016/S0165-0327(98)00051-2
Drennan, M. D., Klauber, M. R., Kripke, D. F., & Goyette, L. M.
(1991). The effects of depression on the Horne-Ostberg morning-
ness-eveningness score. Journal of Affective Disorders, 23, 93-98.
doi:10.1016/0165-0327(91)90096-B
Dworak, M., DiplSportwiss, S. T., Bruns, T., & Strüder. H. K. (2007).
Impact of singular excessive computer game and television exposure
on sleep patterns and memory performance of school-aged children.
Pediatrics, 120, 978-985. doi:10.1542/peds.2007-0476
Gaina, A., Sekine, M., Hamanishi, S., Chen, X., Kanayama, H., Yama-
gami, T., Williams, W. R., Heins, E., Seitz, C., Schüz, J., Toschke, A.
M., Harth, K., Letzel, S., & Böhler, E. (2007). Bedtime, television
and computer habits of primary school children in Germany. Ge-
sundleitswesen, 69, 151-157.
Giannotti, F., & Cortesi, F. (2002). Sleep patterns and daytime func-
tions in adolescence. An epidemiological survey of Italian high-
school student population. In M. A. Carskadon (Ed.), Adolescents
sleep patterns: Biological, social and psychological influences (pp.
132-147). New York: Cambridge University Press.
Harada, T. (2004). Effects of evening light conditions on salivary me-
latonin of Japanese junior high school students. Journal of Circadian
Rhythms, 2, 1-5. doi:10.1186/1740-3391-2-4

M. KREJCI ET AL. 680
Harada, T. (2008). Diurnal rhythms and sleep habits of Japanese chil-
dren and students aged 0 – 25 yrs—Focusing on environmental fac-
tors including those related to 24 h commercial society. Journal of
Chronobiology, 14, 35-43.
Harada, T., & Takeuchi, H. (2001). Epidemiological study on diurnal
rhythms and sleep habits of Japanese children and students aged 6 –
25 yrs. Journal of Chronobi ology, 7, 36-46.
Harada, T., Tanoue, A., & Takeuchi, H. (2006). Epidemiological stud-
ies on dreams, sleep habits and mental symptoms in students aged 18
- 25 years and the 24 hours a day commercialization of Japanese so-
ciety. Sleep and Biological Rhythms, 4, 274-281.
doi:10.1111/j.1479-8425.2006.00232.x
Harada, T., Hirotani, A., Maeda, M., Nomura, H., & Takeuchi, H.
(2007). Correlation between breakfast tryptophan content and morn-
ingness-eveningness in Japanese infants and students aged 0 - 15 yrs.
Journal of Physiological Anthropology, 26, 201-207.
doi:10.2114/jpa2.26.201
Harada, T., Inoue, M., Takeuchi, H., Watanabe, N., Hamada, M.,
Kadota, G., & Yamashita, Y. (1998). Study on diurnal rhythms in the
life of Japanese University, junior high and elementary school stu-
dents including morningness-eveningness preference. Bulletin of
Faculty of Education, Kochi University Series 1, 56, 1-91.
doi:10.3928/00904481-20080701-07
Herman, J. (2008). Circadian rhythm disorders in pediatrics. Pediatric
Annals, 37, 488-496. doi:10.1111/j.1365-2869.2005.00463.x
Higuchi, S., Motohashi, Y., Liu, Y., & Maeda, A. (2005). Effects of
playing a computer game using a bright display on presleep physio-
logical variables, sleep latency, slow wave sleep and REM sleep.
Journal of Sleep Research, 14, 267-273.
doi:10.1080/07420520701657730
Hirata, F. C., Oliveira-Lima, M. C., Sales-de-Bruin, V. M., Nσbrega, P.
R., Wenceslau, G. P., & Carvalhedo-de-Bruin, P. F. (2007). Depres-
sion in medical school: the influence of morningness-eveningness.
Chronobiology Internat i o nal, 24, 939-946.
Honma, K., & Honma, S. (1998). A human phase-response curve for
bright light pulses. Japanese Journal of Psychiatry and Neurology,
42, 167-168.
Japan Parents and Teachers Association (2007). Association research
reports on the consciousness of Japanese children and media. To-
kyo: Japan Parents and Teachers Association, 1-168.
Kagamimori, S. (2006). Epidemiological aspects of self-reported sleep
onset latency in Japanese junior high school children. Journal of
Sleep Research, 15, 266-275. doi:10.1111/j.1365-2869.2006.00530.x
Mori, A. (2002). Electric game hazard on human brains. Tokyo: The
Publication Department, The Japan Broadcasting Corporation, 1-200.
Portaluppi, F., Smolensky, M. H., & Touitou, Y. (2010). Effects and
methods for biological rhythm research on animals and human be-
ings. Chronobiology International, 27, 1911-1929.
Punamaki, R.-L., Wallenius, M., Nygård, C.-H., Saarni, L., & Rimpela,
A. (2007). Use of information and communication technology (ICT)
and perceived health in adolescence: The role of sleeping habits and
waking-time tiredness. Journal of Adolescence, 30, 569-585.
doi:10.3109/07420528.2010.516381
Randler, C. (2008). Morningness-Eveningness comparison in adoles-
cents from different countries around the world. Chronobiology In-
ternational, 25, 1017-1028. doi:10.1016/j.adolescence.2006.07.004
Smyth, J. M. (2007). Beyond self-selection in video game play: An ex-
perimental examination of the consequences of massively multi-
player online role-playing game play. Cyberpsychology and Behav-
ior, 10, 717-721. doi:10.1080/07420520802551519
Takeuchi, H., Morisane, H., Iwanaga, A., Hino, N., Matsuoka, A., &
Harada, T. (2002). Effect of daytime light conditions on sleep habits
and morningness-eveningness preference of Japanese students aged
12 - 15 years. Psychiatry and Clinical Neurosciences, 56, 225-226.
doi:10.1089/cpb.2007.9963
Tazawa, Y., & Okada, K. (2001). Physical signs associated with exces-
sive television-game playing and sleep deprivation. Pediatrics Inter-
national, 43, 647-650. doi:10.1046/j.1440-1819.2002.00983.x
Tonetti, L., Fabbri, M., & Natale, V. (2008). Sex difference in sleep-
time preference and sleep need: a cross-sectional survey among Ital-
ian pre-adolescents, adolescents, and adults. Chronobiology Interna-
tional, 25, 745-759. doi:10.1046/j.1442-200X.2001.01466.x
Torsvall, M. D., & Åkerstedt, T. A. (1980). Diurnal type scale con-
struction, consistency and variation in shift work. Scand Journal of
Work Environment and Health, 6, 283-290.
doi:10.1080/07420520802394191
Van Den Bulck, J. (2004). Television viewing, computer game playing,
and internet use and self-reported time to bed and time out of bed in
secondary-school children. Sleep, 27, 101-104.
Wada, K., Krejci, M., Ohira, Y., Nakade, M., Takeuchi, H., & Harada,
T. (2009). Comparative study on circadian typology and sleep habits
of Japanese and Czech infants aged 0 - 8 years. Sleep and Biological
Rhythms, 7, 218-221. doi:10.1111/j.1479-8425.2009.00397.x
Waldhauser, F., Weiszenbacher, G., Tatzer, E., Gisinger, B., Wald-
hauser, M., Schemper, M., & Frisch, H. (1988). Alterations in noc-
turnal serum melatonin levels in humans with growth and aging.
Journal of Clinical Endocri n ol og y and Metabolism, 66, 648-652,
doi:10.1210/jcem-66-3-648
Wei, R. (2007). Effects of playing violent videogames on Chinese
adolescents’ pro-violence attitudes, attitudes toward others, and ag-
gressive behavior. Cyberp sy ch ol ogy and Behavior, 10, 371-381.
doi:10.1089/cpb.2006.9942
Wiater, A., Lehmkuhl, G., Mitschke, A., & Fricke-Oerkermann, L.
(2008). Sleep, behavior and school performance in children.
Padiatrische Praxis, 71, 397-408.
Yokomaku, A., Misao, K., Omoto, F., Yamagishi, R., Tanaka, K., Ta-
kada, K., & Kohyama, J. (2008) A study of the association between
sleep habits and problematic behaviors in preschool children. Chro-
nobiology International, 25, 549-564.
doi:10.1080/07420520802261705
Zhdanova, I. V., Wurtman, R. J., Lynch, H. J., Ives, J. R., Dollina, A.
B., Morabito, C., Matheson, J. K., & Schomen, D. L. (1995). Phar-
maco-dynamics and drug action; sleep-induced effects of low doses
of melatonin ingested in the evening. Clinical Pharmacology and
Therapy, 57, 552-558. doi:10.1016/0009-9236(95)90040-3