Influence of Limitedly Visible Leafy Indoor Plants on the Psychology, Behavior, and Health of Students at a Junior High School in Taiwan

Abstract

There is growing evidence to support the notion that contact with nature is helpful for emotional states, attention, mental fatigue, behavior, and personal health. This study adopts a quasi-experimental approach to investigate the effects of limitedly visible indoor plants on students' psychology, physiology, and behavior and uses a control-series design covering one semester. Two classes of sophomores at a Taiwanese junior high school (eighth grade, N = 76), of which one served as the experimental group and the other as control, were surveyed once every 2 weeks. After six plants were placed at the back of the classroom, the experimental group had immediately and significantly stronger feelings of preference, comfort, and friendliness as compared to the control group. Also, the experimental group had significantly fewer hours of sick leave and punishment records due to misbehavior than the control group. In addition to the visual and psychological mechanisms that contributed to restoration, there may have been other factors at work.

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Environment and Behavior
DOI: 10.1177/0013916508314476
2008;
2009; 41; 658 originally published online May 5,Environment and Behavior
Ke-Tsung Han
School in Taiwan
Psychology, Behavior, and Health of Students at a Junior High
Influence of Limitedly Visible Leafy Indoor Plants on the
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Influence of Limitedly
Visible Leafy Indoor Plants
on the Psychology, Behavior,
and Health of Students at a
Junior High School in Taiwan
Ke-Tsung Han
National Chin-Yi University of Technology
There is growing evidence to support the notion that contact with nature is
helpful for emotional states, attention, mental fatigue, behavior, and personal
health. This study adopts a quasi-experimental approach to investigate the
effects of limitedly visible indoor plants on students’ psychology, physiology,
and behavior and uses a control-series design covering one semester. Two
classes of sophomores at a Taiwanese junior high school (eighth grade,
N = 76), of which one served as the experimental group and the other as con-
trol, were surveyed once every 2 weeks. After six plants were placed at the
back of the classroom, the experimental group had immediately and signifi-
cantly stronger feelings of preference, comfort, and friendliness as compared
to the control group. Also, the experimental group had significantly fewer
hours of sick leave and punishment records due to misbehavior than the con-
trol group. In addition to the visual and psychological mechanisms that con-
tributed to restoration, there may have been other factors at work.
Keywords: preference; comfort; friendliness; sick leave; misbehavior
Introduction
Modern life, especially urban living, is often characterized by competi-
tion and a hectic pace, which can cause a great deal of pressure (Francis &
Cooper Marcus, 1991; Lewis, 1990). According to research, feelings of
Environment and Behavior
Volume 41 Number 5
September 2009 658-692
© 2009 SAGE Publications
10.1177/0013916508314476
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hosted at
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658
Author’s Note: The author wishes to express great appreciation to the anonymous reviewers
for their valuable comments. Please address correspondence to Ke-Tsung Han, Department of
Landscape Design and Management, National Chin-Yi University of Technology, No. 35, Ln.
215, Sect. 1, Chung Shan Rd.,Taiping, Taichung, Taiwan 41111; e-mail: kthan@ncut.edu.tw.
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 659
pressure, anxiety, and stress have a negative impact on psychological and
physiological health (Evans & Cohen, 1987; Francis & Cooper Marcus,
1991). It is estimated that the United States spends more than $100 billion
each year on medication for stress-related illnesses (O’Donnell & Harris,
1994; Satuter, Murphy, & Harrell, 1990). In addition, an overload of infor-
mation, excessive stimulants, and a lack of tranquility in modern urban life
can cause continual distraction and a shortened attention span. As early as
1978, Simon pointed out that attention was a limited and valuable resource
for humans in modern civilization. The exhaustion of that attention has
been termed “mental fatigue” by Kaplan and Kaplan (1989). Generally speak-
ing, mental fatigue can cause distraction and reduced performance (Cohen &
Spacapan, 1978; Glass & Singer, 1972; Neuchterlein, Parasuraman, & Jiang,
1983; Parasuraman, 1986), negative emotions (Cimprich, 1992; Kuo &
Sullivan, 2001b) such as irritability and tension (Warm & Dember, 1986),
impulsiveness and hostility (Donnerstein & Wilson, 1976), or even behav-
ior such as aggression and violence (Kuo & Sullivan, 2001b). Mental
fatigue can also impede cognition, such as a lessened ability to take in
information and to interpret and react (Cohen & Spacapan, 1978;
Mackworth, 1948; Parasuraman, 1986).
Students, in particular, frequently need to focus their attention on study-
ing, doing assignments, and preparing for examinations despite outside dis-
tractions and wandering thoughts. Therefore, they are highly vulnerable to
the risk of increasing mental fatigue. This is typically the case in Taiwan.
After completing the 9 years of mandatory education, most students in
Taiwan will spend another 3 years at senior high schools or vocational
schools and possibly another 4 years at universities or colleges. In addition,
deeply influenced by the tradition of Confucianism, people in Chinese soci-
eties attach great importance to academic performance (Hau & Salili, 1991;
Lee, 1996; Wong, 1991a). As a result, students in Chinese societies may
face substantially more pressure regarding studying, examinations, and
educational competition than students in Western societies (Biggs, 1991;
Morris, 1985; Wong, 1991b). Accordingly, the research of Tennessen and
Cimprich (1995) shows that after taking an examination, college students
show a reduced capacity for attention and an increase in mental fatigue. Not
surprisingly, attention deficiency is the major reason for unsatisfactory aca-
demic performance (Mantzicopoulos, 1995; Rowe & Rowe, 1992). Studies
have also shown that the classroom environment plays a role in influencing
students’ learning and academic performance (Fraser, 1986, 1991, 1994;
Goh & Fraser 1997). Therefore, an ideal learning environment should pro-
mote attention focusing, reduce mental fatigue and psychophysiological
stress, and ideally even improve health and encourage better learning
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660 Environment and Behavior
and/or examination scores, though in actuality little attention has been paid
to the physical factors of learning environments (Gifford, 1997).
Recent studies have indicated that contact with nature, even if only visual,
is beneficial for mood, aids recovery from mental fatigue, and improves
behavior and health (Faber Taylor, Kuo, & Sullivan, 2001; Hartig, Mang, &
Evans, 1991; Kaplan, 1995; Wells, 2000). The state of reduced mental fatigue
and recovery of attention is referred to as a “restorative experience” (Kaplan
& Kaplan, 1989). In a broad sense, contact with nature is defined as having
some natural elements—such as vegetation, bodies of water, or blue skies—
within one’s sight (Kaplan, Kaplan, & Ryan, 1998). The contact period is
generally not specified, as even a short contact period with nature can provide
temporary relief from attention depletion and psychophysiological stress in
ordinary daily life, producing a microrestorative experience.
If natural elements can actually reduce mental fatigue and psychophysiolog-
ical stress, then vegetation in a learning environment should be able to help
students decrease negative emotions, increase positive feelings, relieve physical
stress, enhance attention, and even improve examination scores and reduce sick
leave and misbehavior. Nonetheless, very few existing studies have explored
these possible effects on students, excepting the research by Lohr, Pearson-
Mims, and Goodwin (1996) as well as Hung and Chang (2002). The former
study focused on the influence of interior plants at a computer laboratory on col-
lege students’ task performance, attention, and stress reduction. The latter one
aimed at the influence of classroom greenness on the attention span of kinder-
garten children. In addition, given that most of the studies on the benefits of
nature or vegetation only focus on short-term and/or immediate responses of
participants, researchers have advocated the necessity of studying longer term
effects (Hietanen & Korpela, 2004). Moreover, the existing studies and theories
primarily focus on the benefits of visual contact with nature and seemingly
ignore the positive effects of exposure to live plants. Vision and/or psychologi-
cal mechanisms might not be the only factor contributing to human well-being
and/or health (Fjeld, Veiersted, Sandvik, Riise, & Levy, 1998; Lohr & Pearson-
Mims, 1996). This study, therefore, examines the effects of limitedly visible
plants in a classroom on students’psychology, behavior, and health, and explores
the influence patterns of the indoor plants over a longer period of time.
Empirical Research of the Psychophysiological
Benefits of Nature on Humans
According to recent studies of human–environment interaction, nature—
particularly vegetation—has positive effects on emotion, physiology, cognition,
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behavior, and health (Han, 2003; Hartig et al., 1991; Kaplan, 1995). The
following is a summary of sampled findings.
Effects on Emotion
Two surveys conducted in Sweden indicated that visual and/or physical
access to and use of natural settings at either workplaces or near homes
reduced the level of experienced stress, irrespective of gender, age, or
socioeconomic factors (N = 953, Grahn & Stigsdotter, 2003; N = 656,
Stigsdotter, 2004). Hartig et al.’s (1991) research indicated that both pro-
longed and shortened periods of interaction with nature (simulated or actual)
were conducive to stress recovery as measured by affective self-reports.
Stiles (1995) investigated the perceptions of hospital patients in a large wait-
ing room under two conditions: with and without interior plants. The results
showed that patients perceived the waiting room with plants as significantly
more relaxing, welcoming, and cheerful and less stressful. In addition, a
field experiment randomly exposed 81 participants to different amounts of
plants in an office. This experiment indicated that indoor office workers’
emotions were more positive when real plants were present than when no
plants were present (Larson, Adams, Deal, Kweon, & Tyler, 1998).
Effects on Physiology
Orsega-Smith, Mowen, Payne, and Godbey (2004) collected data from
100 elderly American adults (age >50) regarding their park visits and psy-
chophysiological states for 5 days using a diary survey. They found that
those who stayed in the parks longer had lower systolic blood pressure as
measured by an electric sphygmomanometer and that this relationship was
independent of daily stress level. Nakamura and Fujii (1990) measured
unstressed participants’ EEG in the alpha frequency range while they
viewed four kinds of images: potted plants with or without flowers, the
same pot without plants, or a cylinder similar to the pot. They found that
the participants’ alpha activity was greater when viewing potted floral
plants, second-most active when observing potted plants without flowers,
and least active when seeing the pot without plants. This result suggested
that participants were less aroused physiologically and more relaxed but
wakeful during exposure to natural simulations. Similarly, a laboratory
experiment conducted by Chang and Chen (2005) in Taiwan compared 38
college students’ psychophysiological reactions to slides of an indoor office
with the presence of window views (none, city, and nature) as well as with
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the presence of indoor plants. Their results suggested that participants
exposed to nature were less nervous, as indicated by the objective measure
of blood volume pulse and the subjective measure of state anxiety. In addi-
tion, Lohr et al. (1996) conducted an experiment using 96 undergraduates as
participants at a windowless college computer lab with plants either present
or absent. They found that the participants had lower systolic blood pressure
readings when plants were present than when they were not present.
Effects on Cognition
An Internet survey in the United States collected parental evaluation of
the symptoms for children with attention deficit/hyperactivity disorder
(ADHD) with respect to the children’s activity environments. The results
obtained from 452 responses indicated that “green” outdoor settings signif-
icantly reduced ADHD symptoms even when the variations of activities and
demographic factors, such as gender, age, income, residency, and disorder
severity, were taken into account (Kuo & Faber Taylor, 2004). An experi-
ment conducted by Shibata and Suzuki (2002) in Japan found that 146 col-
lege students performed better on an association task when presented with
real plants than when none were present. Similarly, the results of Lohr
et al.’s (1996) experiment indicated that the participants were 12% faster in
reaction time on a computer task that objectively measured their mental
processing and reported more perceived attention when with indoor plants
than when none were present. Ottosson and Grahn (2005) conducted a field
experiment at a geriatric care center in Sweden. They found that the 15
elderly residents (average age 86) performed better on cognitive tasks after
visiting a nearby garden than after resting in their rooms. Moreover, Kuo
and Sullivan (2001b) and Kuo (2001) reported that among the 145 inner-
city residents of a Chicago public housing area, those who lived in green
conditions had higher scores on a cognitive test than their counterparts liv-
ing in more barren settings. Hung and Chang (2002) observed children’s
behavior at a kindergarten in Taiwan and found that the vegetation in the
classroom increased the children’s attention and reduced distraction.
Effects on Behavior
Mooney and Nicell (1992) compared the behaviors of Alzheimer residents
at two types of healthcare facilities in Canada: with and without gardens. As
indicated by the nurses’ records, the rate of violence and behavioral incidents
were decreased in the institutions with gardens, whereas they increased
662 Environment and Behavior
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considerably in the institutions without gardens. Kuo and Sullivan (2001b)
found that the 145 interviewed residents who lived in apartments with more
nature nearby reported less aggression and violence against their family
members than those who lived in comparatively barren buildings, as indi-
cated by a self-report scale. Faber Taylor, Wiley, Kuo, and Sullivan (1998)
reported that among 262 children observed, those who played in green court-
yards had higher levels of creative play than those in comparatively barren
outdoor spaces. Similarly, other studies suggested that the greener those out-
door open spaces were, the larger and more mixed were the groups of resi-
dents that used them (96 observations, Coley, Kuo, & Sullivan, 1997) and that
greener environments engendered more socializing or neighborly activities in
nearby residents (N = 145, Kuo, Sullivan, Coley, & Brunson, 1998b; N = 91,
Kweon, Sullivan, & Wiley, 1998; 758 observations, Sullivan, Kuo, &
DePooter, 2004). Also, Kuo and Sullivan (2001a) found that of 98 apartments
in Chicago, where the apartments had more surrounding nature, residents
reported fewer property and violent crimes to the police.
Effects on Health
The results of surveying 3,144 senior residents in Tokyo indicated that
after 5 years the survival rate of the respondents who had green spaces
nearby was significantly higher than that of those who did not, and that this
effect was independent of socioeconomic variables (Takano, Nakamura, &
Watanabe, 2002). In Moore’s (1982) study, prisoners whose windows
looked out on nearby farmlands and forests reported fewer sick calls than
those whose window views looked out on the prison courtyard. Similarly,
West (1985) found that prisoners having window views of natural settings
had fewer stress-related physical symptoms, such as headaches and indi-
gestion, than the prisoners having window views restricted to other prison
buildings. Furthermore, Fjeld and associates (1998) recruited 51 healthy
indoor office workers at a Norwegian company to participate in their exper-
iment. They found that the participants reported significantly less neu-
ropsychological and mucous membrane symptoms when their offices had
plants present. Also, Ulrich (1984) compared health outcomes of 23
matched patients who had undergone gall bladder surgery and were recov-
ering in a room with one of two types of window views. The postoperative
patients whose rooms had a window facing a natural setting dominated by
trees took fewer potent analgesics and were released from the hospital sooner
than those whose windows overlooked a man-made setting dominated by
brown brick walls.
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Major Theories of the Psychophysiological Benefits of
Nature on Humans
Currently there are two major theories concerning the benefits of nature
for humans. One is the Kaplans’ attention restoration theory (Kaplan &
Kaplan, 1989). The other is Ulrich’s psychological–evolutionary theory
(1983). Despite small differences, these two theories share many similari-
ties because both of them are in line with evolutionary theory, Berlyne’s
psychobiology (1960, 1963, 1971), and information processing concepts
(Hartig, 1993; Parsons, 1991).
According to evolutionary theory, owing to millions of years of evolu-
tion in natural environments, humans have developed a psychological
mechanism of adaptive responses to nature. Particularly, humans react most
favorably to certain contents and patterns of the natural environment, such
as vegetation and water (Ulrich & Parsons, 1992, p. 96). Also, both theories
adopt a psychological perspective of human–environment interaction as a
means to search for suitable habitats that provide necessary resources such
as water and vegetation, contain low risk factors, and can sustain survival,
reproduction, and well-being. All this vital environmental information is
perceived visually by humans. Thus, quick responses to visual information,
such as preference, attention, and reaction, are conducive to human survival
and evolution. Both theories further hypothesize that in addition to visual
aesthetic responses, contact with nature can evoke more diversified positive
reactions, feelings of well-being, and effective functioning. The subtle dif-
ferences between these two theories are summarized below.
Attention Restoration Theory
Kaplan and Kaplan’s theory emphasizes that to ensure effective daily
functioning, humans need to maintain cognitive clarity, which requires
directed attention. However, each individual has a limited store of attention
that is depleted by extensive use. In general, attention fatigue results in low-
ered competence and functioning efficiency (Hartig et al., 1991).
Fortunately, attention depletion can be restored. A place where mental
fatigue can be restored is referred to as a restorative environment (Kaplan
et al., 1998). Restorative environments include a wide range of settings
from wilderness to indoors, and are found on a variety of different scales.
Nevertheless, environments that contain natural components, particularly
vegetation and water, seem to be especially helpful for the reduction of
mental fatigue (Kaplan, Bardwell, & Slakter, 1993; Kaplan et al., 1998).
664 Environment and Behavior
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 665
Kaplan and Kaplan identify four features of restorative environments:
being away, extent, fascination, and compatibility. If an individual spends
sufficient time in an environment possessing these four components, he or
she will experience four progressive levels of restoration. The first level is
referred to as “clearing the head,” which allows random thoughts to wander
in the head and gradually fade away (Kaplan & Kaplan, 1989, p. 196; cf.
Kaplan et al., 1998). At the second level, the depleted attention is gradually
recharged. At the third level, one can hear unattended thoughts or matters
on one’s mind, owing to the reduced internal noise and enhanced cognitive
quiet, which are facilitated by “soft fascination.” The final and the deepest
level is one that tends to evoke “reflections on one’s life, on one’s priorities
and possibilities, on one’s actions and one’s goals” (Kaplan & Kaplan,
1989, p. 197).
Psychoevolutionary Theory
Ulrich argues that restoration is derived from the reduction of stress,
instead of from the replenishment of directed attention fatigue (Hartig et al.,
1991). According to him, when people encounter an event or a situation,
they first perceive or appraise it in terms of its influence on their well-being.
If an event or situation is judged or appraised as harmful, threatening, or
challenging, then stress occurs, which usually is accompanied by other neg-
ative emotions (Brannon & Feist, 1997). Under aversive conditions, the
internal equilibrium in body systems is disrupted (Evans & Cohen, 1987).
The physiological functioning in response to stress also consumes energy
and resources, which consequently causes fatigue (Ulrich et al., 1991). In
addition, stress influences behaviors such as avoidance or abnormal perfor-
mance (Cohen, Evans, Stokols, & Krantz, 1986).
Restoration from stress includes recovering from excessively high or
low physiological and psychological conditions and recharging of the
energy consumed in response to stress. According to Ulrich’s theory, if
landscapes, which often contain vegetation and water, can immediately
evoke feelings of mild to moderate interest, pleasure, and calmness, then
they are conducive to restoration from stress (Hartig, Book, Garvill,
Olsson, & Garling, 1996). When exposed to these kinds of settings, one’s
attention is easily attracted, which may block pessimistic thoughts,
replace negative emotions with positive ones, and reequilibrate physio-
logical disturbances (Parsons, 1991). After the positive changes in emo-
tions, reduced cognitive functioning or performance may be regained
(Ulrich, 1993).
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666 Environment and Behavior
Importance and Contribution of This Study
The importance and contribution of this study for human–nature interac-
tions include five aspects. First, most of the existing research on similar topics
was conducted in Western societies, which focused on adults and college
students, with only a few of them recruiting children (Faber Taylor et al., 2001;
Wells, 2000) or adolescents. This study used junior high school students in
Taiwan as the participants. Second, unlike previous studies, this research col-
lected the participants’ data on human responses covering emotion, physiol-
ogy, cognition, behavior, and health simultaneously by using both subjective
and objective measures. Third, this study covered a relatively longer period of
time of contact with nature and explored the change in the influences of nature
through time. Fourth, most of the past studies were conducted at laboratories
and adopted an experimental design that involved simulating outdoor settings.
In contrast, this study focused on indoor environments and adopted a quasi-
experiment in actual classrooms. So far, there are not many discussions in the
literature on the influences of indoor plants on humans, particularly with
respect to classroom greenness. Lastly, unlike previous studies that often
focused on visual contact of photos and slides, or window views of natural
scenery as the treatment, this research used real natural elements of a specified
amount of living plants at the classroom, but which were only limitedly visi-
ble to students. In so doing, the contributed means and/or mechanisms of con-
tact with nature might be further explored. In sum, this study could
complement the insufficiency of past studies in the above-mentioned five
aspects and might shed light on or serve as a pilot for future studies.
Research Method
Hypotheses
Based on the above-mentioned research findings and theories concern-
ing the influence of nature on human emotion, physiology, cognition,
behavior, and health, we are particularly interested in the benefits of expo-
sure to indoor leafy plants beyond the solely visual aspects. Accordingly,
the hypotheses of this study are as follows:
Hypothesis 1: Limitedly visible leafy indoor plants can reduce the
psychophysiological stress of the students.
Hypothesis 2: Limitedly visible leafy indoor plants can enhance cognitive func-
tioning, focus attention, and even improve academic performance of the
students.
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 667
Hypothesis 3: Limitedly visible leafy indoor plants can reduce student
misbehavior.
Hypothesis 4: Limitedly visible leafy indoor plants can reduce hours of
student sick leave.
Hypothesis 5: The influences of limitedly visible leafy indoor plants on
students’ psychology, behavior, and health will change through time.
Research Design
This study adopted a quasi-experimental approach with repeated mea-
sures. Specifically, it was a control-series design that included one experi-
mental group and one control group covering both a baseline phase and a
manipulation phase (Frankfort-Nachmias & Nachmias, 1996). The study
lasted for one semester (from June 6, 2005, to January 21, 2006). During
the study, two groups of students were surveyed using self-administered
questionnaires about every other week for a total of 10 responses per
student. In addition to the self-reported questionnaires, objective data for
each participant were collected, including term examination scores, sick
leave hours, and punishment records due to misbehavior. This research was
divided into two phases: the baseline phase (lasting for approximately 1.5
months with four pretests) and the manipulation phase (lasting for about 2.5
months with six posttests after plants had been placed at the classroom of
the experimental group). Before the study began, the students and their
parents signed forms of consent.
There were three purposes of using the control-series design in this study.
The first one was to compare the experiment and the control groups during the
baseline phase to see if there were any differences. This was particularly
important because this study was a quasi-experiment conducted in the actual
classroom, and could therefore not control all conditions and provide precisely
identical experimental conditions. The second was to investigate whether any
differences existed after the treatment within the experimental group. The third
was to test if there were any differences between the experimental and the con-
trol groups in the perceptions of their classroom environments and their acad-
emic performance during the manipulation phase. The selection of the
experiment and the control groups was randomly decided. The same research
assistant conducted the 10 questionnaire surveys for each group. The two
groups of students filled out the questionnaires during their regular class meet-
ings, which were scheduled at the same hour on the same day. Each time, it
was randomly decided which group would take the questionnaire survey first.
Each questionnaire survey took about 10 minutes to complete.
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Participants
There were three major considerations of participant selection in this
study. First, both groups should have male and female students. Second,
both groups should be similar in education level. Third, both groups should
have similar physical environments in the classroom, such as size, shape,
furniture arrangement, location, lighting, ventilation, noise level, and win-
dow views. The Ching Cheng High School in Changhwa County, Taiwan,
met the above criteria and provided two classes of sophomore students of
its junior high school division as participants (eighth-graders). The class-
rooms of these two classes were both located on the fourth floor of the same
building and were immediately adjacent to each other. The experimental
group had 35 students (26 male and 9 female), with an average age of 13.6.
The control group had 41 students (32 male and 9 female), with an average
age of 13.5. As indicated by the results of an independent t test, both groups
were not significantly different in age (p > .05).
Experiment Treatment
The treatment in this study was six Botel Tobago cinnamon trees
(Cinnamomum kotoense Kanehira et Sasaki) with an average height of 135
cm and a mean canopy width of 80 cm, in total occupying 6% of the class-
room floor plan. These relatively oval-shaped plants were placed in a row
at the back of the classroom of the experimental group, so as to provide to
the students a limited visibility of greenness (Figure 1). The Botel Tobago
cinnamon tree is a small evergreen tree of the Lauraceae family. Both pho-
tophilous and shade-tolerant, this plant thrives at temperatures ranging
from 22 °C to 30 °C. It is strongly adaptive to its environment, with rela-
tively low vulnerability to pests and diseases. It has dense foliage with
shiny green leaves, which together form a moderate texture. This species
does not have obvious flowers, fruits, or fragrance (Xu & Lv, 1984).
Given that there is no study currently available that has reported which
plant is most beneficial to human psychology, behavior, and health, the
major reason for using the Botel Tobago cinnamon tree in this study was it
is highly adaptive, strong, and easy to take care of. These six plants did not
have any blossom or fruit during the experimental period. Their growth was
measured every 1.5 months during the study. According to the results of
ANOVA with repeated measures, the heights and the canopy widths of the
plants did not differ significantly (p > .05) through time. Therefore, if there
was any variation in students’ reactions, it was not possibly caused by the
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 669
plant growth. In addition, the plants were taken care of by assigned staff
whose responsibilities included cleaning fallen leaves, watering plants, and
moving the plants out of the classroom for sunlight during weekends. The
Figure 1
Classroom Environments
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students were not required to take care of the plants, which might have had
its own effect on the students, such as that found in horticultural therapy
(Davis, 1994; Hewson, 1994). Nonetheless, we observed that the students
still interacted with the plants by putting small decorations on the foliage,
such as plastic flowers and colored ribbons.
Measurement Tools
The data in this study were mainly collected through questionnaire sur-
veys that included (a) basic information of the students; (b) the State
Anxiety Inventory (STAI) by Spielberger, Gorsuch, Lushene, Vagg, and
Jacobs (1983); (c) the Restorative Components Scale (RCS) by Laumann,
Garling, and Stormark (2001); (d) the Restoration Scale (RS) by Han
(2003); (e) the Well-Being Measures (WBM) by Kaplan (2001); and (f)
students’ perceptions of their classroom environments in terms of prefer-
ence, attraction, comfort, and friendliness. Using other scholars’ scales that
have proven reliable and valid saved the effort of developing and testing a
new scale. Given that most of the scales were originally written in English,
they were translated into Chinese for the use of this study. To ensure the
Chinese translations were comprehensible to the participants, a pilot study
recruiting seven 1st-year junior high school students was conducted. These
students reported no particular difficulty or problem using these scales. In
addition, because there might be other factors that could influence students’
reactions, this study collected data on the positive and negative events, for
example winning awards or having accidents, that occurred during the
study period as controlling variables.
The STAI is a psychological scale frequently used in clinical practice and
research to measure the immediate anxiety perceived by individuals. It is a
4-point scale containing 20 statements, such as “I feel calm” and “I feel ner-
vous,” among which nine statements are negatively worded (Spielberger et al.,
1983). In calculating the state anxiety of the participants, the scores of the nine
negatively worded statements were first reversed. Then all scores were
summed to form the final index score. A higher index score meant greater anx-
iety felt by the participants. The reliability (Cronbach’s α) of the STAI for the
two participant groups for 10 surveys in this study ranged from .699 to .946.
The RCS is mainly used to measure if an environment is helpful for indi-
viduals to reduce mental fatigue. This scale is based on the four factors of
the Kaplans’ theory. It is a 7-point scale containing 22 statements, for
example “I am in a different setting than usual,” “All the elements constitute
a larger whole,” “There are many objects here that attract my attention,” and
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“I am capable of meeting the challenges of this setting.” The scores of each
of the four factors (being away, extent, fascination, and compatibility) were
averaged to produce a composite score, respectively. The four composite
scores were then averaged to produce the index score. A higher index score
meant greater perceived potential for attention restoration (Laumann et al.,
2001). According to the data collected in this study, the reliability
(Cronbach’s α) of this scale for the 20 surveys ranged from .770 to .954.
The RS is designed to measure the influences of environments on the
psychophysiological stress of individuals. Integrating the theories of the
Kaplans (1989) and Ulrich (1983), this 9-point scale contains eight state-
ments covering the four factors of emotion, physiology, cognition, and
behavior, such as “anxious–relaxed,” “My breathing is becoming faster,” “I
am interested in the present scene,” and “I would like to stay here longer.”
To obtain the index score, the composite score of each of the four factors
was calculated first. Before these four composite scores were averaged, the
composite score of the physiological arousal had to be reversed. A higher
index score meant greater perceived potential for stress recovery (Han,
2003). As indicated by the data collected in this study, the reliability
(Cronbach’s α) of the RS for the 20 surveys ranged from .725 to .871.
The WBM is developed according to the Kaplans’ theory (Kaplan &
Kaplan, 1989), which covers three factors (effective functioning, at peace,
and distracted). This 5-point scale contains 26 statements indicating, for
example, being “able to get really absorbed in a task,” “irritable,” and “losing
or misplacing things,” among which 10 are negatively worded. To calculate
the index score, the scores of the 10 negatively worded statements were first
reversed. Then the composite scores of the three factors were averaged. A
higher index score meant greater overall well-being perceived by the partici-
pants (Kaplan, 2001). According to the data of this study, the reliability
(Cronbach’s α) of the WBM for the 20 surveys ranged from .698 to .965.
Preference was measured from the statement “I like this setting very
much.” Attraction was referenced from “I am attracted to this environment
very much.” Comfort was indicated from “I am very comfortable in this set-
ting.” Friendliness was evaluated from “this environment makes me feel
very friendly.” There was only one statement using a 9-point scale for each
of the four items in the questionnaires. Higher scores meant greater per-
ceptions of the items by the participants. Because there was only one ques-
tion for each of these four items, it was not a multiquestion scale.
Therefore, the reliability could not be calculated.
In addition to the data obtained from the self-reported surveys, this study
collected objective records of each participant to avoid subjectivity. The
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objective data included the scores of three term examinations during the
semester, hours of sick leave, and records of punishment due to misbehav-
ior in the study semester and in the previous semester. Each of the term
examinations covered seven subjects: Mandarin, English, mathematics,
civil ethics, history, geography, and chemistry and physics. Because the dif-
ficulty of the questions of each subject might be varied across the exami-
nations, the scores of the seven subjects were first standardized (Neuman,
2006) and then were averaged to form the students’ academic performance.
Data Screening
To ensure the validity of the questionnaire data, invalid data on the scales
in which (a) the participants indicated the same scores on all questions; (b)
the scores of the statements showed a regular pattern, such as a Z shape; or
(c) the answers to the positively worded and those to the negatively worded
questions were contradictory, were discarded. All the collected subjective
and objective data were analyzed using SPSS 12.0 for windows. The major
statistical analyses included ANCOVA, ANCOVA with repeated measures,
t tests, nonlinear regression, and correlation.
Results
Differences of Subjective Perceptions Between Groups
Baseline phase. Whether or not the two participant groups had equiva-
lent states was examined by running ANCOVAs with repeated measures.
Each of the eight perception scores of the four pretests was specified as a
dependent variable. The participant group was used as an independent vari-
able. The means of both the positive and the negative incidents during the
baseline phase were specified as covariates to control the influences of
other extraneous variance. Before an ANCOVA is conducted, it is necessary
to ensure that the regression slopes of the factors are parallel (Fon, 1992;
Chang, Chang, & Lin, 2003). The regression slope analyses showed that
this premise was met, at which point the eight ANCOVAs were run. As the
results indicated, except for the RS—experimental group mean = 5.250,
control group mean = 4.288, F(1, 37) = 7.684, p = .009—there were no sig-
nificant differences between the two groups in terms of the other seven per-
ceptions. STAI: F(1, 39) = 1.591, p = .215; RCS: F(1, 40) = 0.006, p = .939;
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WBM: F(1, 25) = 0.098, p = .756; preference: F(1, 60) = 1.487, p = .228;
attraction: F(1, 61) = 1.186, p = .280; comfort: F(1, 61) = 2.623, p = .110;
friendliness: F(1, 61) = 2.213, p = .142. That is, except for the RS, the two
classes of students had equivalent states of the seven perceptions during the
baseline phase despite not having the same teachers. Given that the partic-
ipant groups differed in the RS, the comparisons of this response between
the two groups were excluded in the later analyses. In addition, it was found
that when negative events (mean = 0.769) were taken into account, the vari-
ations of the STAI were significantly reduced and therefore increased the
precision of the analysis.
Immediate effects. Past research has focused on the short-term responses
of the participants, and found an immediate and positive effect of vegeta-
tion on human perceptions of the environment. Therefore, after the place-
ment of the six plants at the classroom, the first posttest was intended to
measure the immediate effects of the greenness in this study. The seven per-
ception scores of the first posttest, except for the RS, were used as depen-
dent variables, respectively. The participant group was specified as the
independent variable. The mean of each of the perceptions of the four
pretests, respectively, and the means of the positive and the negative events
during the first posttest period were used as covariates to control the influ-
ences of the baseline phase and other extraneous variance on the partici-
pants. The regression slope analyses showed that none violated the premise
of parallel slopes. The results of the seven ANCOVAs indicated that there
was no significant difference between the experimental and the control
groups in the STAI, RCS, WBM, and in attraction. However, the experi-
mental group had significantly higher scores than the control group in pref-
erence, comfort, and friendliness. This indicated that six indoor plants had
immediate and positive effects on these three perceptions (Table 1). In addi-
tion, it was found that when the means of the seven perceptions of the
pretests (STAI: 46.984; RCS: 3.518; WBM: 3.044; preference: 4.249;
attraction: 3.995; comfort: 4.545; friendliness: 4.532) were taken into
account, they reduced the variations and could therefore enhance the accu-
racy of the ANCOVAs.
Manipulation phase. Whether or not the treatment had positive influ-
ences on the participants over a longer period of time was examined by run-
ning ANCOVAs with repeated measures. The scores of the seven
perceptions of the six posttests were used as dependent variables. The par-
ticipant group was specified as the independent variable. The means of the
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674 Environment and Behavior
perception scores during the baseline phase and the means of the positive
and negative incidents during the manipulation phase were used as covari-
ates. The regression slope analyses showed that all seven perceptions met
the premise and were suitable for running ANCOVAs. The results of the
ANCOVAs with repeated measures indicated that there was no significant
difference between the two groups. STAI: F(1, 23) = 0.095, p = .761; RCS:
F(1, 27 ) = 2.207, p = .149; WBM: F(1, 13) = 1.110, p = .311; preference:
F(1, 48) = 0.001, p = .974; attraction: F(1, 48) = 0.202, p = .655; comfort:
F(1, 48) = 0.019, p = .890; friendliness: F(1, 48) = 0.360, p = .552. This
suggested that the students of both groups were not significantly different
in their long-term perceptions of their respective classroom environments.
Differences of Objective Records Between Groups
Baseline phase. The questionnaire surveys were subjective opinions of
the participants, whereas the term examination scores and records of pun-
ishments due to misbehavior were objective evaluations. The results of
t test with independent samples showed that there was no significant dif-
ference (p = .881) between the experimental and the control group in their
academic performance in the first term examination during the baseline
phase. Given that Ching Cheng High School compiled data of students’ sick
leave hours and punishment records only by semesters, the sick leave hours
Table 1
Comparisons of the First Posttest
Means ANCOVAs
Experimental Control
Subjective Perceptions Group Group Fp
STAI 45.426 42.574 1.633 .208
RCS 3.513 3.502 0.007 .934
WBM 3.215 3.202 0.013 .909
Preference 4.699 3.726 7.827 .007**
Attraction 4.184 3.881 0.910 .344
Comfort 5.381 4.238 10.342 .002**
Friendliness 5.369 4.391 5.269 .025*
Note: STAI = State-Trait Anxiety Inventory; RCS = Restorative Components Scale; WBM =
Well-Being Measure.
*p < .05. **p < .01.
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and punishment records of the two student groups in the previous semester
were also analyzed using t tests with independent samples. The results indi-
cated that these two groups were not significantly different in both records
(sick leaves: p = .273; punishments: p = .589). Therefore, all of these tests
suggested that the experimental and control groups had equivalent levels in
terms of their academic performance, sick leave hours, and behavioral
records before the treatment, even though the two classes of students had
different teachers.
Academic performance during the manipulation phase. As previous
studies have found that contact with nature was conducive to attention
restoration and cognitive functioning, we were interested in examining
whether or not indoor plants might, therefore, improve students’ academic
performance. An ANCOVA with repeated measures was conducted, in
which the academic performance of the first term examination was used as
a covariate, the academic performance of the second and the third term
examinations were specified as dependent variables, and the participant
group was used as the independent variable. The results indicated that
(a) the premise of the parallel regression slopes was satisfied; (b) the two
groups were not significantly different in academic performance, F(1, 75) =
0.660, p = .419; (c) though not significantly different, the experimental
group had better academic performance than the control group (means:
0.036 vs. –0.032); and (d) taking into account the academic performance of
the first term examination (mean: 0.000) could reduce the variations and
enhance the precision of the analysis.
Sick leave hours and punishment records. Two ANCOVAs were con-
ducted to examine if there were any differences between the two groups in
their sick leave hours and punishment records due to misbehavior. The sick
leave hours and the punishment records due to misbehavior in the previous
semester were used as covariates, respectively. The sick leave hours and the
punishment records during the study were specified as dependent variables,
respectively. The participant group was used as the independent variable.
The results showed that (a) the premise of equal regression slopes was met,
(b) the experimental group had significantly fewer sick leave hours and
punishment records than the control group (Table 2), and (c) using covari-
ates (sick leave hours mean: 2.320; punishment records mean: 0.160) could
reduce the variations and increase the accuracy of the analyses. Therefore,
the above findings suggested that classroom vegetation had positive effects
on students’ health and behavior.
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676 Environment and Behavior
Within the Experimental Group
Differences between the baseline and the manipulation phases. The four
pretests of the eight perception scores were averaged to serve as the
students’ overall perceptions of the classroom environment during the base-
line phase. Likewise, the six posttests of the eight perception scores were
averaged to serve as the students’ overall perceptions of the classroom envi-
ronment during the manipulation phase. Then eight paired t tests were con-
ducted. The results showed that the experimental group had improvements
in these eight perceptions after the plants were placed in the classroom, but
these improvements were not statistically significant (STAI: p = .499; RCS:
p = .116; RS: p = .331; WBM: p = .282; preference: p = .479; attraction:
p = .606; comfort: p = .833; friendliness: p = .438). Similarly, a paired t test
compared the academic performance of the first term examination in the
baseline phase and the mean of the academic performance of the second
and the third term examinations in the manipulation phase. The results
showed that the academic performance was better during the manipulation
phase (mean: 0.020) than the baseline phase (mean: –0.018) but this
improvement did not reach the level of statistical significance (p = .559).
Change patterns. The trend of the influences of the indoor plants on the
participants over a longer period of time was explored. Using the six posttest
scores of each of the eight perceptions as the dependent variable, respectively,
and the time sequence as the independent variable, eight nonlinear regression
analyses for curve estimation were performed. All the default options of the
SPSS were selected, which included linear, quadratic, cubic, logarithmic,
inverse, power, compound, S, logistic, growth, and exponentials, to examine
if there was a certain pattern of changes through time. The results indicated
that (a) the model of cubic curve explained the greatest variations in the
Table 2
Comparisons of the Objective Data
Means ANCOVAs
Objective Data Experimental Group Control Group Fp
Sick leave hours 2.149 5.984 11.329 .001**
Punishment records 0.015 0.522 5.208 .025*
*p < .05. **p < .01.
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 677
STAI, RCS, RS, preference, attraction, comfort, and friendliness, of which
their R
2
values ranged from 66% to 94%, none of which was significant (p >
.05); (b) the models of compound, growth, and exponentials were significant
(p < .05) as the RCS and their R
2
values were all 66%; and (c) it was not clear
which model was suitable for the WBM because all models explained an
extremely low and statistically insignificant variation (R
2
values ranged from
0.8% to 4%). All of these suggested that these eight perceptions fluctuated
over time without definite change patterns. Nonetheless, among the eight per-
ceptions, the STAI, RCS (Figure 2, Table 3), RS, preference, and attraction
increased, in general, over time, whereas the WBM (Figure 3, Table 4) and
comfort relatively decreased through time. Friendliness showed equivocal
trends of either upward or downward movement (Figure 4, Table 5). Because
there were only three measures of academic performance for the students’
term examinations, this was not sufficient for the curve estimation of the non-
linear regression analyses.
Subjective Perceptions and Objective Records
Correlation analyses using the participants’ data on subjective percep-
tions and objective records were conducted. The results indicated that the
relationships between the eight perceptions and the sick leave hours and
misbehavior records were all insignificant and weak (|r|<.4; p > .05) for
both groups of the participants (Table 6).
Discussion
For students, a learning environment is regarded as a setting full of
authority, rules and regulations, as well as a place for social recognition
Table 3
Regression Models of the Restorative Components Scale
Equation R
2
Fdf1 df 2 p Constant b1 b2 b3
Cubic .978 7.476 3 2 .120 3.197 0.600 –0.202 0.022
Compound .663 7.865 1 4 .049 3.530 1.022
Growth .663 7.865 1 4 .049 1.261 0.022
Exponential .663 7.865 1 4 .049 3.530 0.022
Logistic .663 7.865 1 4 .049 0.283 0.979
Note: b1, b2, and b3 are parameter estimates.
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678 Environment and Behavior
Figure 2
Estimated Curves of the Restorative Components Scale
Figure 3
Estimated Curves of the Well-Being Measure
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 679
Figure 4
Estimated Curves of Friendliness
Table 4
Regression Models of the Well-Being Measure
Equation R
2
Fdf1 df 2 p Constant b1 b2 b3
Linear .008 0.031 1 4 .868 3.457 –0.006
Logarithmic .014 0.056 1 4 .824 3.461 –0.022
Inverse .016 0.063 1 4 .814 3.417 0.049
Quadratic .040 0.063 2 3 .940 3.532 –0.062 0.008
Cubic .044 0.031 3 2 .991 3.478 0.007 –0.015 0.002
Compound .008 0.034 1 4 .862 3.457 0.998
Power .015 0.062 1 4 .815 3.461 –0.007
S .017 0.070 1 4 .804 1.228 0.015
Growth .008 0.034 1 4 .862 1.240 –0.002
Exponential .008 0.034 1 4 .862 3.457 –0.002
Logistic .008 0.034 1 4 .862 0.289 1.002
Note: b1, b2, and b3 are parameter estimates.
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680 Environment and Behavior
(Taylor, Peplau, & Sears, 2006). Chinese societies in particular attach great
importance to academic performance. Under the influence of a traditional
Chinese culture with such sayings as “There is nothing more important than
studying,” the classroom might indeed be a major source of psychophysio-
logical stress for students at junior high schools. The results of this study
showed that the effects of six limitedly visible plants on students were not
as influential as expected and that the influences did not seem to have any
certain pattern of changes through time. The following are discussions of
these findings, which also attempt to shed some light on the theories and/or
mechanisms of restoration.
Influences of the Indoor Plants
Visibility and greenness. This study found that even six limitedly visible
plants in the classroom had an immediately significant and positive influ-
ence on the students’ perceptions of preference, comfort, and friendliness.
Previous studies made similar findings of the immediate effects of more
visible vegetation. Nevertheless, an overall positive effect of the greenness
on the eight perceptions and the academic performance of the participants
was not found for the entire manipulation phase. Maybe this was because
the positive effects of the plants did not last through time. Another possible
reason was that vision is indeed the major factor responsible for the posi-
tive effects of nature to occur as the Kaplans (1989) and Ulrich (1983)
advocate. Although the placement of the vegetation provided limited visual
Table 5
Regression Models of Friendliness
Equation R
2
Fdf1 df 2 p Constant b1 b2 b3
Linear .014 0.057 1 4 .823 5.394 0.020
Logarithmic .007 0.030 1 4 .871 5.511 –0.041
Inverse .078 0.340 1 4 .591 5.349 0.285
Quadratic .533 1.713 2 3 .319 6.179 –0.568 0.084
Cubic .664 1.317 3 2 .459 6.986 –1.583 0.420 –0.032
Compound .015 0.062 1 4 .816 5.383 1.004
Power .006 0.026 1 4 .881 5.500 –0.007
S .074 0.321 1 4 .601 1.676 0.052
Growth .015 0.062 1 4 .816 1.683 0.004
Exponential .015 0.062 1 4 .816 5.383 0.004
Logistic .015 0.062 1 4 .816 0.186 0.996
Note: b1, b2, and b3 are parameter estimates.
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Table 6
Correlations Between Two Objective Records and Eight Perceptions
STAI RCS RS WBM Preference Attraction Comfort Friendliness
Experimental group (n = 35)
a
Sick leave hours –.106 –.295 –.185 –.230 –.315 –.268 –.227 –.214
.532 .081 .274 .171 .058 .109 .177 .152
Control group (n = 41)
Sick leave hours –.074 –.023 .067 .155 .028 .003 –.010 –.072
.645 .888 .676 .332 .862 .986 .949 .654
Punishment records .060 .050 –.062 .087 .250 .256 .189 .194
.709 .755 .699 .588 .116 .106 .236 .225
Note: The correlations are based on the objective records of the whole semester and the means of the 10 surveys of the perceptions. STAI = State-
Trait Anxiety Inventory; RCS = Restorative Components Scale; RS = Restoration Scale; WBM = Well-Being Measure.
a. Because the punishment records are constant, correlations cannot be calculated.
681
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682 Environment and Behavior
access to greenness, this gave us a unique opportunity to explore its influences
other than through visual means.
In addition, the plants only occupied 6% of the floor plan of the classroom,
which perhaps was not sufficient to create a natural setting. Researchers found
that the larger the quantities of visible vegetation, the better the effect of anx-
iety reduction (Yu & Lin, 1999) and that greater visibility of tree canopies
could evoke stronger positive responses (Buhyoff, Gauthier, & Wellman,
1984; Lien & Buhyoff, 1986; Schroeder, 1989). If there were greater quanti-
ties of and/or better visibility of classroom greenness, it might have been pos-
sible to find both immediate and long-term significant influences of the plants
on the students’ psychophysiological states and academic performance.
Whether the physical or the visible amounts of plants play a more important
role in human responses might be an interesting topic for future research.
Spatial density. Although the indoor plants did not change the social
density of the classroom (the student number did not change accordingly),
it still reduced the activity space for the students and therefore increased the
spatial density (e.g., Gifford, 1997). Nonetheless, the increased spatial den-
sity due to the plants was relatively limited in this study; the average class-
room floor plan per student decreased by only 0.1 m
2
. Therefore, the
negative impacts of high spatial density on academic performance and
behavior (Glass & Smith, 1978; Loo, 1976; Maxwell, 2003) and blood
pressure (Hackworth, 1976) of students should not have occurred in this
study. It is perhaps worthwhile to further probe the interactions between
classroom greenness, spatial densities, and student responses.
Classroom atmosphere. When the students were scolded by the teachers for
any behavior that might damage the plants, this might have caused extra stress
for the students, increased the disciplinary requirements of the teachers on the
students, and consequently produced a negative classroom climate according
to our observations. This study focused only on the physical factors of the
classroom environment, such as indoor plants, classroom size, and furniture
arrangement, and it neglected factors such as teacher–student interactions and
classroom atmosphere. Some scholars suggest that the classroom climate
plays a stronger role than the physical features of the classroom on students’
emotions and their preferences for the environment (Chang, 1996). Had data
been collected on classroom climate and taken into account in the analyses, it
might have helped to further investigate the interactions between the plants as
a physical element in the classroom, the psychosocial environment of the
place, and the students’ perceptions of the setting and their responses.
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Repeated measures. This study was the first attempt to explore the influ-
ences of the indoor plants on the students for a whole semester with 10
repeated measures. Although the participants were instructed to report how
they felt about their learning settings in which they spent more than 8 hr on
each of the weekdays and which included a variety of activities, some of the
students might have found filling out the same questionnaire every other
week boring or even repulsive. This might have consequently influenced
their feelings, which in turn impeded the possible positive effects of the
plants in this study.
Subjective perceptions and objective records. According to the findings
of this study, classroom greenness had immediate and positive influences
on the students’ perceptions, but its influences seemed not to last for long.
However, the sick leave hours and punishment records due to misbehavior
of the experimental group were indeed significantly less than those of the
control group, which corresponded to the results of past studies (e.g., Kuo
& Sullivan, 2001b; Ulrich, 1984). Please recall that the students’ objective
records were not closely related to those of their long-term subjective per-
ceptions. The possible reasons for this inconsistency are that (a) the posi-
tive effects of the plants were not readily and consciously sensible to the
participants; (b) all the above-mentioned factors, such as the spatial density,
classroom climate, or repeated measures, influenced the students’ percep-
tions of the classroom but not their objective performances; and (c) per-
ceptions, health, and/or behaviors triggered by nature might be through
various means and have differing mechanisms. Further identifying and dis-
tinguishing these mechanisms might be fruitful for related theories and
practices of human well-being.
Caution should be advised as to the findings of this study. The objective
data on sick leave hours and misbehavior records were compiled for one
whole semester, in which the manipulation phase lasted only for about two-
thirds of the semester. In addition, this study used the sick leave hours and
punishment records due to misbehavior from the previous semester as covari-
ates, rather than those in the baseline phase. Given that there are not many
empirical studies exploring the influences of interior plants on human health
and behaviors, this study might serve only as a reference for further research.
Self-reported questionnaires. Among the eight perceptional responses
collected in this study, preference, attraction, comfort, and friendliness
were evaluated with only one question, each of which has a closely corre-
sponding term in Chinese. It was found that the plants had immediate and
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significant influences on preference, comfort, and friendliness. All the
scales, STAI, RCS, RS, and WBM, were originally written in English and
were developed in Western societies. Although these four scales have been
proven for their reliability and validity in the past and have also shown good
reliability (Cronbach’s α≥.7) as indicated by the data collected in this
study, it still cannot be completely verified that these self-reported scales
actually measure participants’ emotions, comfort, restoration, or well-
being. Moreover, the role of the differences of language and/or culture
between Chinese and English, which might play a role in the significant
versus the insignificant responses, is worth further investigation.
Novelty. Given that even such a weak treatment of only six limitedly vis-
ible indoor plants could have some immediate positive influences, further
efforts should pare down the possible effects of novelty—merely “some-
thing new” —in contrast to specific greenness. Various interventions
including nothing, a pleasant but nonnatural stimulus (e.g., posters of pop-
ular movie stars or singers), an unpleasant nonnatural stimulus (e.g., pic-
tures of unsightly buildings), an unpleasant natural stimulus (e.g., photos of
slime mold), and a pleasant natural stimulus (e.g., pictures of flowering
plants) could be used to examine whether the vegetation adds anything to
the effect of a novel stimulus.
Change Patterns
The responses of the six posttests for the experimental group fluctuated,
which reveals no definite pattern of change through time. In general, most
of the eight perceptions exhibited a relatively slight increasing trend,
whereas a few indicated a slight decreasing trend. Because this study
adopted a quasi-experimental design in the actual environment, which was
an open system, it could not control for all variables. As a result, the
students might still have been influenced by other variables rather than by
the indoor plants alone, which caused the absence of an obviously consis-
tent trend. Even though this study was probably the first attempt to collect
data by using repeated measures over a relatively longer period of time, six
data entries still might be too few to reveal a clear pattern of change.
Related Theories
Both the theories of the Kaplans (1989) and of Ulrich (1983) extend the
positive responses of humans to nature to factors such as emotion, attention,
684 Environment and Behavior
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well-being, and daily functioning (Hartig, 1993). This study found that lim-
itedly visible leafy indoor plants enhanced the students’ perceptions of pref-
erence, comfort, and friendliness and reduced their sick leave hours and
punishment records due to misbehavior. These findings support the
common notion of the Kaplans and Ulrich that the benefits of contact with
nature broadly cover many dimensions. However, the results of this study
seem to be slightly favorable to Ulrich’s emphasis on emotions, particularly
for preference. Yet, no significant difference of the STAI was found.
With respect to theories and/or mechanisms of restoration, the findings of
this study suggest that (a) vision and psychology are the major means for the
positive effects of nature to occur, as the previous studies indicate; (b) the
evoked positive influences cover progressive levels starting likely with emo-
tions, particularly preference; and (c) given that the visible greenness is lim-
ited and the relationships between the objective records and the subjective
perceptions are all insignificant and either weakly positive or negative, the
mechanism of restoration is not purely visually and psychologically driven as
the Kaplans and Ulrich advocate. Among the above issues, other sources con-
ducive to well-being and functioning that cannot be visually detected, such as
oxygen, humidity (Fjeld et al., 1998), particulate accumulation and air qual-
ity improvement (Lohr & Pearson-Mims, 1996), and even Pythoncidere pro-
duced by plants, might deserve particular consideration in a comprehensive
mechanism of human recovery from psychophysiological stress.
Suggestions and Conclusion
Suggestions
The above-mentioned limitations and/or issues could serve as a pilot for
future endeavors. The most ideal and strictest research method is a field
experiment in which participants are randomly assigned to actual settings.
Yet, there are still many difficulties to overcome in this approach, because
most elementary and junior high schools in Taiwan have small classes, with
fewer than 40 students. Meanwhile, because students need to learn so many
course subjects, it is almost practically impossible to recruit classes that
have the same teachers. In addition, students are not randomly assigned to
the class, but are often grouped by level. Furthermore, summer and winter
breaks will interrupt the continuance of a long-term study, not to mention the
likely biases due to repeated measures over short intervals with only a minor
element added to the setting. Lastly, for any scale intended to measure
Han / Influence of Indoor Plants on Psychology, Behavior, and Health 685
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human restoration or functioning, it is necessary to examine whether the
measurement results are consistent with the actual changes in the human
body and mind (Han, 2003; Herzog, Maguire, & Nebel, 2003).
An alternative approach to the above-mentioned issues would be to adopt
an interrupted time series design with multiple replications on a random
schedule (Shadish, Cook, & Campbell, 2002). A single class of students could
serve as its own experiment and control group. The experimental treatments of
no change, visible plants, less visible plants, simulated nature, and stimuli of
pleasant nonnature, unpleasant nonnature, and unpleasant nature could be ran-
domly scheduled and placed in the classroom for the same period of time. The
participants’ responses of both subjective perceptions and objective perfor-
mances could be collected at the same intervals. This research design, similar
to a completely randomized within-participant study, is effective and powerful
for a quasi-experiment that is unable to find an equivalent control group (Cook
& Campbell, 1979; Shadish et al., 2002). In addition to examinations of nov-
elty effects, the class of students can be classified into groups according to how
close they are next to live plants. Thus, if there are other effects due to the
plants, the effects might be a function of the distance from the plants.
Hopefully, in addition to whether or not the visible or the physical amount of
greenness is more influential to humans, other sources of live plants contribute
to human well-being and/or health, for example oxygen or humidity (Fjeld
et al., 1998), and consequently, whether there are other such mechanisms
responsible for psychophysiological restoration might be further explored.
After the positive influences of greenness on humans, except for novelty,
are confirmed, the next step is to investigate which types and species of veg-
etation, their arrangements and amounts, are most favorable to psychophysi-
ological well-being. Furthermore, detailed features of the vegetation, such as
shape, canopy width, color, texture, height, flower, fruit, and fragrance can be
explored to determine which combinations of these factors can specifically
meet different human needs, for example with respect to age, gender, occu-
pation, in terms of emotion, physiology, cognition, behavior, or health.
Although research on such topics has emerged only recently and now receiv-
ing more and more attention, it is hoped the research findings will soon be
applicable to the design practices of environments for daily life.
Conclusion
This study attempted to use limitedly visible leafy indoor plants to
influence students’ perceptions of the classroom. However, their emotions
and perceptions of the environment could be possibly influenced by other
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Han / Influence of Indoor Plants on Psychology, Behavior, and Health 687
variables. In general, the findings of this study correspond to those of pre-
vious research that used more visible vegetation and are in agreement with
the theories of the Kaplans (1989) and Ulrich (1983) that exposure to
nature even with six plants or 6% greenness of floor plan is beneficial for
human emotions, behavior, and health. Some issues remain that warrant
further examination: (a) effects of greenness per se except for novelty; (b)
specific minimum thresholds of greenness to evoke diverse positive
responses; (c) how these influences change over time; (d) whether it is the
physical or the visible amount of plants that is more conducive to positive
reactions; and (e) in addition to visual perception and psychological mech-
anism of restoration, what other factors are helpful for well-being and
functioning.
Because of assignments, homework, and examinations, students are
often both psychologically and physiologically stressed. Given that class-
rooms play a vital role in influencing students’ learning and academic per-
formance, a classroom that meets students’ needs and is preferred by
students can improve students’ quality of education. If a classroom can pro-
vide more opportunities for contact with nature, a more harmonious atmos-
phere, and adequate space for students, it might help students develop a
healthy body and a healthy mind through situational education. In so doing,
educational goals might be more easily reached.
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Ke-Tsung Han is associate professor of the Department of Landscape Architecture and
Management at the National Chin-Yi University of Technology, Taiwan. His current research
interests focus on restorative environment and Feng Shui.
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