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Effects of foliage plants on human physiological and psychological responses at
different temperatures
Desto Jumeno and Hiroshi Matsumoto
Citation: AIP Conference Proceedings 1649, 32 (2015); doi: 10.1063/1.4913541
View online: http://dx.doi.org/10.1063/1.4913541
View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1649?ver=pdfcov
Published by the AIP Publishing
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Effects of Foliage Plants on Human Physiological and
Psychological Responses at Different Temperatures
Desto Jumeno1,a, Hiroshi Matsumoto2,b
1,2Department of Architecture and Civil Engineering, Toyohashi University of Technology, Toyohashi, Japan
1Jurusan Teknik Industri, Universitas Andalas, Padang, Indonesia
a)destojmn@gmail.com
b)matsu@ace.tut.ac.jp
Abstract. Escalation of task demands and time pressures tends to make a worker run into work stress, which leads to mental
fatigue and depression. The mental fatigue can be reduced when attention capacity is restored. Nature can serve as a source of
fascination which can restore the attention capacity. People bring plants indoors so they can experience nature in their
workplace. The stress and fatigue are also affected by air temperatures. The increase or decrease of temperatures from the
comfort zone may induce the stress and fatigue. The objective of this study is to investigate the intervention of using foliage
plants placed inside a building at different air temperature levels.
The effects of foliage plants on human stress and fatigue were measured by human physiological responses such as heart
rate, amylase level, electroencephalography (EEG), and the secondary task-reaction time. Several different tasks, namely
typing, math and logical sequences are included in the investigation of these studies. Fifteen subjects, with the age ranged
from 22 to 38 years old have participated in the study using within subject design.
From the study, it is revealed that the presence of foliage plants at several temperatures have different effects on
meditation, secondary task reaction time and typing accuracy. This study also revealed that the presence of plants on several
types of tasks has different effects of attention which are useful for increasing work performance.
Key words: foliage plant, temperature, stress, attention, EEG
INTRODUCTION
Strong competition in business necessitates companies to streamline their operation which in turn producing an
increase in task demand. At the same time companies are also required to react to customer’s demand as fast as
possible, producing time pressures to workers. Escalation of task demands and time pressures tends to make a
worker run into work stress, which leads to mental fatigue and depression. The mental fatigue can be reduced when
attention capacity is restored. Nature can serve as a source of fascination which can restore the attention capacity
(1). For psychological restoration people are more favored to natural environment rather than urban environment
(2). People bring plants indoors so they can experience nature in their workplace. The increase in the number of
indoor plants may increase the impressions of the employees on their environment (3). Furthermore, other previous
studies also reveal that the presence of plants can reduce stress of the employee, health complaint, and increase
employee’s satisfaction and quality of working life (4–8). Therefore, the interaction of human with plants affects
human attitudes, behaviors and physiological responses.
Another means to cure depression and anxiety is by meditation. Meditation promotes relaxation, both for mind
relaxation and muscle relaxation, compassion and patience. Meditation also prevents one from being stressed or
cures one from a depression. People have long been studying meditation using electroencephalography/EEG (9).
Meditation is generally characterized by increasing alpha waves and theta waves and accompanied by a decrease in
the other waves. However, the way these waves occur at work, is still in question. There is a possibility that
meditation waves are not only occurring while one is not doing or thinking something, but also occur at work.
EEG also can be used for measuring attention (10). Attention can be determined using beta wave (14-30 Hz).
Not alike with meditation, when a person is attentive there is a greater beta wave (11). Moreover, attention also can
be measured using secondary task reaction time or STRT (12) and accuracy (13).
The stress and fatigue are also affected by air temperatures. A specified range of air temperature together with
humidity and air movement constitutes a comfort zone. According to ASHRAE 55-2010, the acceptable operating
temperatures are 20 – 25.5 oC in winter and 23 – 28 oC in the summer. The increase or decrease of temperatures
from the comfort zone may induce the stress and fatigue and may affect performance and safety. In Japan, the most
common comfort temperature is around 25oC. To maintain indoor temperature at this level, people use an air
conditioner in the summer and a heater in the winter. However, the use of an air conditioner and a heater requires
The Irago Conference 2014
AIP Conf. Proc. 1649, 32-40 (2015); doi: 10.1063/1.4913541
© 2015 AIP Publishing LLC 978-0-7354-1291-0/$30.00
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considerable amount of energy. The presence of indoor plants may affect the perception comfort of the occupant at
different temperatures. Thus, the presence of indoor plants may reduce the amount of energy required to maintain
the room stays in the comfort condition. However, most studies on the effect of foliage plants on human
physiological and psychological responses have been conducted in the prescribed temperature. No study on the
effect of plants on human physiological and psychological responses at different temperatures was found.
The objective of this study is to investigate the intervention of using indoors foliage plants on attention and
meditation at different air temperature levels. The study also investigated the effect of plants at several types of
tasks. Three types of tasks were investigated, namely typing, math and logics. Characteristics of tasks in the studies
on the effect of foliage plants on human physiological and psychological responses has been investigated in the
previous study (14).
In this study, the effect of plant on attention is measured using EEG and STRT (secondary task reaction time).
The study hypothesized that the presence of plants at different temperature levels has no effect on physiological and
psychological responses as well as the performance and accuracy of the subject.
METHOD
In this study, an experiment was conducted using a within subject design or a repeated measures design. The
independent variables (IV) of the experiment are plant and temperature. There were 2 levels of plant and no plant
conditions, and 3 levels of temperature, which is 22oC, 25oC, and 28oC. The dependent variables (DV) of the study
were human physiological responses such as heart rate, amylase level, electroencephalography (EEG), the secondary
task-reaction time (STRT), and task performance. There were 4 conditions tested in the experiment:
1. No plant condition, at temperature of 25oC
2. 6 foliage plants at temperature of 22oC
3. 6 foliage plants at temperature of 25oC
4. 6 foliage plants at temperature of 28oC
The condition of no plant and with the presence of plants is presented in Fig. 1. The experiment took place in the
Natural Energy Building at Toyohashi University of Technology. The space of the climatic chamber is 3.57 meters
long, 2.67 meter wide and 2.44 meter high. The illuminance of the room was 408 lx, by two fluorescent lamps
without any daylight, measured at desk level.
Plants used in the experiment were aglaonema commutatum, calathea concinna, spathyphillum, epiremnum
aureum, benjamin, and scheflera arboricola. Plant heights were varied between 25 cm and 50 cm. All plant leaves
are green. Foliage plants are located on the desk, 80 cm – 120 cm from the subject position.
Fifteen subjects, with the age ranged from 22 to 38 years old participated in the study. All participants were
postgraduate students from various departments. All participants have lived in Japan for at least 2 years, so they all
have been acclimatized to the subtropical weather. All subjects participated in all conditions.
(a)
(b)
FIGURE 1. Room condition (a) without plant, (b) with the presence of plants
A subject only participated in the experiment two times maximum in a day during the experiment. To overcome
learning bias, randomization was carried out so that the sequence of conditions was different for one subject to the
other. Several different tasks, namely typing, math and logical sequences are included in the investigation of these
studies. The sequence of tasks also was randomized for each trial.
Before performing the first task, the subject was given 10 minutes for acclimatization with room condition,
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because the temperature and humidity in the experiment room may be different with the outdoor temperature and
humidity. Each task lasted for 10 minutes, followed by taking rest for 5 minutes. The total time required for each
subject in each experimental session is 60 minutes.
Heart rate and body temperature were measured before and after each task. Body temperature was measured
inside the ear. Heart rate was measured near the chess using Polar S610i. Body temperature measured using Jintan
thermometer.
EEG measured by using Brainwave Visualizer from NeuroSky, Inc. EEG data were taken 5 times when the
subject is conducting the prescribed task from a monitor located outside the chamber. The EEG sensor and the
monitor are wireless. The EEG sensor sends signals through bluetooth to an android apps monitor called Brainwave
Visualizer. The outputs from Brainwave Visualizer apps are meditation wave’s rating and attention wave’s rating.
The scale of rating is from 0 to 100. Fatigue and stress were measured by using NIPRO amylase monitor, before
and after the experiment. A disposable stick for measuring amylase score was placed in the mouth, under the tongue,
for 30 seconds.
Secondary task reaction time (STRT) is conducted during the primary task. During the primary task, there would
be sound signals generated from a computer that can be heard by the subjects using an earphone. When the subject
hears the sound signal (secondary signal), he or she was instructed to react to the signal by pressing the “enter” key
on the keyboard. STRT data were taken 4 times when the subject is conducting the prescribed task. After all tasks
has been finished, the subject then fills out the questionnaire.
Schedule of the experiment is presented in Fig. 2. The experiment was conducted in the summer (from July to
September 2014). Each experiment lasted for about 60 minutes.
FIGURE 2. Schedule of experiment
RESULTS
The experiment was conducted during the summer, with outside temperature from 20oC to 33oC. Climatic
conditions of the experiment are presented in Table 1.
TABLE 1. Conditions during the experiment
Variables
Measurement
Temperature (inside chamber)
22, 25 and 28oC
Temperature (outside)
20-33oC
Humidity (inside chamber)
49.6 - 60%
Humidity (outside)
73 – 88 %
Air speed (at air conditioner)
2.45 m/s
Air speed (at air ventilator)
0.8 m/s
Air speed (at working height)
0.01 m/s
Illuminance (at working height)
400 lx
Clothing insulation index
0.54 clo
Green coverage ratio
9.55%
In Table 2, the effects of plants on physiological responses and performances were presented. From Table 2, it
can be seen that there is a significant effect of task type on the secondary task reaction time (p < 0.05). A significant
effect of the interaction of plant and task type on the secondary task reaction time (p < 0.005) is also found in this
study.
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TABLE 2. The effect of plants on physiological responses and performances
Independent Variable
Dependent Variable
F value
Degree of freedom
Significance
Plant
Task
Plant x Task
Heart rate
1.377
1.970
0.527
2
2
4
0.260
0.179
0.602
Plant
Task
Plant x Task
Attention
1.528
1.124
3.146
2
2
4
0.237
0.355
0.077
Plant
Task
Plant x Task
Meditation
0.839
0.618
0.291
2
2
2
0.375
0.554
0.752
Plant
Task
Plant x Task
Average body
temperature
1.147
1.966
2.123
2
2
4
0.302
0.179
0.159
Plant
Amylase
0.022
1
0.884
Plant
Task
Plant x Task
Reaction Time
0.310
4.321
9.598
1
2
2
0.587
0.036*
0.003*
Plant
Typing accuracy
0.454
1
0.512
Plant
Typing speed
1.154
1
0.301
Plant
Math productivity
0.075
1
0.788
Plant
Math accuracy
0.984
1
0.338
Plant
Logic productivity
0.035
1
0.853
Plant
Logic accuracy
0.012
1
0.916
The effect of room air temperatures on physiological responses and performances is presented in Table 3. From
Table 3, it can be seen that variable temperature has a significant effect on meditation. Fig. 3 depicts further the
relationship between temperature, meditation waves’ rating and tasks. From Fig. 3, it can be seen that the meditation
waves’ rating at 25oC temperature is higher than the waves’ strength in the other temperatures. It can be seen also
that the pattern of meditation waves’ rating for every task is the same, suggesting that 25oC is the optimal
temperatures for the brainwaves to feel relax.
It also can be seen from Table 3 that variable task has a significant effect on attention. Fig. 4 depicts further how
the attention waves’ rating for each task has a different level. From Fig. 4, it can be seen that attention waves’ rating
in math has a higher level than the attention wave's rating on the other tasks. Also, the attention waves’ rating in the
typing task has a lower level than attention waves’ rating on the other tasks.
From the experiment, a significant effect of room air temperature on average body temperature is shown in Table
3. The relationship between the room air temperature and the average body temperature is shown in Fig. 5. From
Fig. 5, it can be seen that the average body temperature is increased as the room air temperature increased, and the
pattern of the three tasks is almost similar.
As can be seen from Table 3, a significant effect of temperature on reaction time was found. Reaction time
measured in this experiment is secondary task reaction time (STRT) which is a measure of attention. Fig. 4 shows
the effect of temperature on the average reaction time. From Fig. 6, it can be seen that reaction time was lower in
25oC then in the other temperatures. From Fig. 6, it also can be seen that reaction time in typing task is higher than
that in the other tasks.
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Moreover, it also can be seen from Table 3 that temperature has a significant effect on typing accuracy. Fig. 7
shows further the relationship between typing accuracy and air temperature. From Fig. 7, it can be seen that the
typing accuracy increases with the air temperature. However, for the female, the optimum temperature is 25oC.
TABLE 3. The effect of temperatures on physiological responses and performances
Independent Variable
Dependent Variable
F value
Degree of freedom
Significance
Temperature
Task
Temperature x Task
Heart rate
0.285
0.005
0.21
2
2
4
0.754
0.995
0.932
Temperature
Task
Temperature x Task
Attention
1.15
3.78
0.36
2
2
4
0.348
0.050*
0.829
Temperature
Task
Temperature x Task
Meditation
3.92
0.83
0.361
2
2
4
0.032*
0.448
0.835
Temperature
Task
Temperature x Task
Average body
temperature
32.19
1.00
3.357
2
2
4
0.00*
0.394
0.050*
Temperature
Task
Temperature x Task
Reaction Time
6.19
0.028
0.727
2
2
4
0.014*
0.972
0.593
Temperature
Typing accuracy
3.34
2
0.050*
Temperature
Typing speed
1.40
2
0.283
Temperature
Math Productivity
1.13
2
0.356
Math accuracy
0.554
2
0.589
Temperature
Logics productivity
0.492
2
0.623
Logics accuracy
1.31
2
0.287
In the comparison of temperature levels shown in Fig. 3 – Fig. 7, 22oC temperature is worse than the other
temperature levels almost in all dependent variables, except for attention wave strength and secondary task reaction
task on the math task. Temperature of 25oC was the best in meditation wave rating, and also in secondary task
reaction time for logic sequence and typing tasks. Temperature of 28oC was the best for attention wave rating on the
logic sequence and typing tasks, and also the typing accuracy.
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FIGURE 3. The effect of temperature on meditation
FIGURE 4. The effect of temperature on attention
FIGURE 5. The effect of Room air temperature on attention
61#
62#
63#
64#
65#
66#
67#
68#
69#
70#
71#
22# 25# 28#
Medita'on*waves*ra'ng*
Temperatures*(oC)*
Typing#
#Math#
Logics#
54#
56#
58#
60#
62#
64#
66#
68#
70#
22# 25# 28#
A8en'on*waves*ra'ng*
Temperatures*(oC)*
Typing#
Math#
Logics##
35.4#
35.6#
35.8#
36#
36.2#
36.4#
36.6#
22# 25# 28#
Average*Body*Temperature*
(oC)*
Room*Air*Temperature*(oC)*
Typing#
Math#
Logics#
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FIGURE 6. The effect of temperature on reaction time
FIGURE 7. The effect of temperature on typing accuracy
DISCUSSION
From the EEG analysis, it is revealed that the type of task has a significant effect on attention, whereas
meditation is significantly affected by temperatures. In this study, the subject paid more attention in math task than
that in the logic task and in the typing task. Solving math problem requires attentiveness and concentration, which
associated with beta brainwave (14 to 30 Hz). The difference in height of beta waves between solving math
problems, logic sequence, and typing task, shows that brain cells and neuron are working harder in solving math
problems task than logic sequence and typing tasks. Higher level of attentiveness and concentration is required for
solving math problems because this kind of thinking uses only the left side of the brain continuously and work only
with numbers and then recall solution from the long term memory. It differs from solving logic task which uses also
the other side of the brain to find solution, which is not only work on numbers but also pictures, positions and
nonstandard figures. It also differs from typing task, which use less portion of the load in the brain, but also
distributing the load to both hands and eyes. The results of this study on the effect of task types on attention are
consistent with the results of Shibata & Suzuki (2002), which compared association task and sorting task. In their
results, the subject paid more attention in the association task than that in the sorting task. It also shows that the
association task requires more thinking than the sorting task.
1#
1.2#
1.4#
1.6#
1.8#
2#
2.2#
2.4#
2.6#
2.8#
22# 25# 28#
Average*Reac'on*Time*(second)*
Temperature*(oC)*
Typing#
Math#
Logics#
55#
60#
65#
70#
75#
80#
85#
90#
95#
100#
22# 25# 28#
Typing*Accuracy*(%)*
Temperature*(oC)*
Female#
Male#
Average#
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From the result of this study, it is also important to see the phenomenon that when the subject solving math
problems, meditation waves (alpha and theta) exceeds attention wave (beta). It is against the general premise that
beta waves are identical with thinking aloud, while the alpha and theta waves synonymous with rest and tranquility.
This is not to say that the beta wave is equal to zero when the subject solving math problems. This fact shows that
the brain of human generates several brainwaves at different frequencies and rating simultaneously. As brain
constructed in several parts and different parts account for different kind of thinking, it may be seen that at the same
time, different parts of the brain generating different brainwave. For example, when the front left is active it
produces beta waves, but at the same time the other side of the brain is at rest and it produces alpha and theta waves.
The results of this study also revealed that temperatures have a significant effect on meditation. Subject working
in a chamber with foliage plants at 25oC temperature has a higher rating of meditation waves (alpha and theta) than
working in a chamber with foliage plants at 22oC and 28oC. With relative humidity of 49%-59%, temperature of
25oC is the most comfortable temperature condition for an office. Therefore, at this temperature the brain is more
easily to produce slower brain waves frequency like alpha and theta (4-13 Hz). This result also shows that the effect
of temperature on meditation waves is stronger than the effect of plants. If the effect of plants is stronger than the
effect of temperature, it can be expected that the meditation waves at 28oC are higher or the same with the
meditation waves at 25oC.
Furthermore, a significant effect of temperatures on subject's secondary task-reaction time was found in the
study. The results of this study show that reaction time on 25oC is shorter than reaction time on 22oc and 28oC. The
reaction is a secondary task in the experiment and is used to measure attention. Shorter reaction time means that the
subject has more resource for attention, thus has a better attention or is less stressful. This result also implied that the
effect of temperature on attention is stronger than the effect of plants. If the effect of plants is stronger than the
temperature, it can be expected that the reaction time at 28oC is shorter than that at 25oC.
The results of this study also show that temperature has a significant effect on typing accuracy. The accuracy of
typing increased with the temperature. However, there was no such difference in accuracy between 25oC and 28oC.
It might be expected that difference in accuracy might be caused by plants rather than by temperature. As, it is
suggested that 25oC is a desirable comfort temperature compared to 28oC, so the accuracy in 25oC should not be
lower than the accuracy at 28oC, if the temperature is expected to have a larger effect of the typing accuracy. Higher
accuracy in typing task may mean better concentration and attentiveness, because the subject got less number of
errors. It means that attentiveness in typing at temperature 25oC and 28oC is better than at temperature 22oC.
For typing accuracy and reaction time (STRT), both are affected by temperatures, whereas reaction time also
affected by the task and interaction of plants and task. Prinzmetal, McCool and Park (2005) also showed that
reaction time and accuracy reveal different mechanisms. Temperature and the presence of plants are noninformative
cues which form involuntary attention, whereas the task is informative cues which form voluntary attention.
The results of this study also show that the most suitable temperature for various tasks and variable is different.
Temperature of 22oC is best for achieving attention on the math task. Temperature of 25oC is best for meditation and
attention, or is least stressful at all tasks, especially in logic sequence task and typing tasks. Temperature of 28oC is
best for attention on the logic sequence task and typing tasks, and also for typing accuracy.
The limitation exists in the levels of temperature in this study. Three different temperatures within the range of
comfort were examined in this study. A further study can be conducted in the other level of temperatures, such as
outside the range of comfort, or at temperatures closer to the desirable temperature of 25oC. Also, this study only
measure brainwave while the subject is working. Further study can be conducted to measure brainwave during the
rest period so that the effect of plants on recovery can be investigated.
CONCLUSION
In conclusion, this study has investigated the effect of foliage plants on human physiological and psychological
responses at different temperatures and over several types of tasks. Satisfactory results have been obtained proving
that the presence of foliage plants at several temperatures has different effects on meditation, secondary task
reaction time (STRT) and typing accuracy. This study also revealed that the presence of plants on several types of
tasks has different effects of attention which are useful for increasing work performance.
The present study has only investigated three levels of temperatures within the range of comfort, 22oC, 25oC, and
28oC in summer. Consequently, a further study on the effect of smaller range of temperatures in various seasons is
required. Such research will sharpen the knowledge in this area and provide the best foundation for designing work
and its environment.
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ACKNOWLEDGEMENT
This study was funded by Directorate General of Higher Education, Ministry of National Education,
Indonesia. Also, this work has been supported by the Grant-in-Aid for Scientific Research (B) No. 26289202
of the Ministry of Education, Science, Sports and Culture (MEXT). We are grateful for their support. All
plants used in this study were provided by PLANET Co. Ltd. Japan. The authors would like to acknowledge
students and laboratory members of Toyohashi University of Technology for their participation in this study.
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