Transient decreases in blood pressure and heart rate with increased subjective level of relaxation while viewing water compared with adjacent ground

Abstract

Over the course of human evolution, the successful detection of drinking water in arid environments mitigated the physiological stress of dehydration and acted as a strong source of natural selection for recognizing the optical cues for water and perhaps physiological indices of relief. The current research consisted of two studies investigating whether viewing water in outdoor settings affected autonomic tone and subjective ratings of relaxation. The first study examined blood pressure and heart rate of 32 participants who focused their attention on water in a swimming pool, a tree in a parking lot, and a small sign over a busy street. The results of this study showed that viewing water for 1 min 40 sec. reduced blood pressure reliably compared with viewing the tree and sign. Heart rate was also lower reliably while viewing water than the sign. The second study extended this research to a university arboretum, recording blood pressure, heart rate, and subjective ratings of relaxation of 73 participants successively at six sites along a 1.62 km path next to a creek, two small lakes, and the adjacent ground with open grassy areas and trees. At each site, participants alternated randomly in viewing the water or the ground first. Averaged for the six sites, analyses showed that the systolic/diastolic ratio for blood pressure and heart rate were reliably lower when viewing the water compared with the adjacent ground, an effect associated with the subjective rating of relaxation. Together, these findings indicate that viewing water can affect autonomic tone in a way that might account for the subjective rating of relaxation.

Full text

Journal of Environmental Psychology 81 (2022) 101794
Available online 15 March 2022
0272-4944/© 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Transient decreases in blood pressure and heart rate with increased
subjective level of relaxation while viewing water compared with
adjacent ground
Richard G. Coss
*
, Craig M. Keller
Department of Psychology, University of California, Davis, USA
ARTICLE INFO
Handling Editor: L. McCunn
Keywords:
Blood pressure
Heart rate
Relaxation response
Sympathetic tone
Visual xation
Water perception
ABSTRACT
Over the course of human evolution, the successful detection of drinking water in arid environments mitigated
the physiological stress of dehydration and acted as a strong source of natural selection for recognizing the
optical cues for water and perhaps physiological indices of relief. The current research consisted of two studies
investigating whether viewing water in outdoor settings affected autonomic tone and subjective ratings of
relaxation. The rst study examined blood pressure and heart rate of 32 participants who focused their attention
on water in a swimming pool, a tree in a parking lot, and a small sign over a busy street. The results of this study
showed that viewing water for 1 min 40 s reduced blood pressure reliably compared with viewing the tree and
sign. Heart rate was also lower reliably while viewing water than the sign. The second study extended this
research to a university arboretum, recording blood pressure, heart rate, and subjective ratings of relaxation of
73 participants successively at six sites along a 1.62 km path next to a creek, two small lakes, and the adjacent
ground with open grassy areas and trees. At each site, participants alternated randomly in viewing the water or
the ground rst. Averaged for the six sites, analyses showed that the systolic/diastolic ratio for blood pressure
and heart rate were reliably lower when viewing the water compared with the adjacent ground, an effect
associated with the subjective rating of relaxation. Together, these ndings indicate that viewing water can affect
autonomic tone in a way that might account for the subjective rating of relaxation.
1. Introduction
The objective of the current research was to determine if viewing
water in a landscaped setting engendered a transitory reduction in
autonomic arousal and a subjectively experienced relaxation response.
Its heuristical framework was founded on the physiological properties of
the relaxation response involving the balance of parasympathetic and
sympathetic activity that mediates the variability in blood pressure and
heart rate (see Benson, Beary, & Carol, 1974; Sakakibara, Takeuchi, &
Hayano, 1994; Taylor, Goehler, Galper, Innes, & Bourguignon, 2010;
Zagon, 2001). With regard to habitat perception, pictures of spacious
landscapes were used as low-arousal controls by Hess (1975) to examine
how provocative pictures enhanced sympathetic arousal measured by
pupillary dilation. Related research using pupillary dilation measures
(Coss, Clearwater, Barbour, & Towers, 1989, p. 102242) showed that
landscape scenes in projected slides with the greatest apparent depth,
especially those showing mountains in the distance and water in the
foreground, lowered sympathetic arousal and received higher prefer-
ence ratings compared with pictures with the least apparent depth.
Based on this study, 285 photographic prints derived from these slides
were displayed for a one-year period on the workstation walls of
crewmembers at two Australian Antarctic research stations and sampled
for attitude changes at 3-month intervals. Landscape scenes with water
and other glittery properties engendered slower habituation and higher
subjective ratings of relaxation than dry landscape scenes (Clearwater &
Coss, 1991). Relevant to this research, an earlier study by Ulrich (1981)
had shown that viewing projected slides of landscape scenes with water
produced more wakefully relaxed brain activity compared with urban
scenes as interpreted from electroencephalographic recordings of
alpha-wave amplitude; however, there was no evidence that these slides
induced a difference in heart rate. When considered together, these
ndings inspired the current study of the physiological effects of water
perception conducted in an outdoor setting.
* Corresponding author. 807 Falcon Ave., Davis, CA, 95616, USA.
E-mail addresses: rgcoss@ucdavis.edu (R.G. Coss), craigkeller24@gmail.com (C.M. Keller).
Contents lists available at ScienceDirect
Journal of Environmental Psychology
journal homepage: www.elsevier.com/locate/jep
https://doi.org/10.1016/j.jenvp.2022.101794
Received 28 June 2021; Received in revised form 9 March 2022; Accepted 11 March 2022

Journal of Environmental Psychology 81 (2022) 101794
2
1.1. Sources of natural selection for evolved water perception
Routine access to water is critical to the survival for many species
that are not well adapted to arid and semi-arid environments (cf. de Beer
& van Aarde, 2008; Rosinger, 2019; Scholz & Kappeler, 2004; Sigg &
Stolba, 1981). The success of nding drinking water on a daily basis to
regulate thermal balance and prevent dehydration played a substantial
role in shaping hominin evolution for greater energetic efciency in
mobility (Behrensmeyer & Reed, 2007; Falk, 1990; Newman, 1970;
Ruff, 1994; Wheeler, 1993). This change in hominin mobility is roughly
coincidental with the decline of lake levels, decreases in humid forests
and the expansion of grassland-savanna habitats during the Late Plio-
cene (cf. Bobe & Behrensmeyer, 2004; Kingston & Harrison, 2007). In
humans, dehydration is a major stressor, activating the autonomic
nervous system for thermal regulation that engenders parasympathetic
withdrawal and sympathetic activation that increases blood pressure
and cardiac output (Schlader & Charkoudian, 2018). As argued by Coss
and Moore (1990), successful detection of water in this stressful context
followed by rehydration would likely have had a substantial effect on
the evolution of perceptual systems for identifying distal and proximal
cues for water in arid habitats. During the dry season in southern Africa,
for example, the relief from thermal stress with rehydration is evident in
exited bathing behavior of intraspecic groupings of migratory un-
gulates in water holes (Coss, pers. observ. Etosha Natl. Park, Namibia,
2008).
Historical dependency on nearby water is suggested by the presence
of hominin fossils near large lakes (e.g., Spoor et al., 2007) that include
footprints in lake margins (Behrensmeyer & Laporte, 1981; Roach et al.,
2016; Hatala et al., 2017). No hunter-gatherers are recorded in envi-
ronments with rainfall less than 90 mm per year (Beyer, Krapp, Eriksson,
& Manica, 2021). Although it is unknowable whether early Homo
actually bathed in lakes for thermal regulation, modern humans have
directed immense architectural resources at facilitating bathing as a
presumed pleasurable activity (e.g., Roman Republic baths, see Yegül,
2013).
Children are delighted with outdoor bathing (
Ľ
ubomíra & Matúˇ
s,
2017) and exhibit a preference for landscape photographs showing
water compared with drier landscapes (Zube, Pitt, & Evans, 1983). Coss
and Moore (1990) observed infants mouthing mirrored toys and quan-
tied adult preferences for paper with glossy and sparkling surface
nishes that appear to connote wetness compared with mat and sandy
nishes. Follow-up research supported the aforementioned conjecture of
partially innate water perception by documenting that young infants
will mouth glossy metal and plastic plates on their hands and knees not
unlike the prone postures of children in developing countries drinking
from rain pools (see Fig. 1 in Coss, Ruff, & Simms, 2003). Further evi-
dence of innate water-perception properties is found in observations
that some patients with nal-stage Alzheimer’s disease will mouth
glossy spoons more than forks, mouth glossy table tops and hand rail-
ings, and they can be hesitant to walk on dark, glossy asphalt paths that
appears wet (Coss et al., 2003, p. 200). Such behavioral retrogenesis
(Borza, 2014) reects the re-expression of infantile reexes with loss of
higher-level neural organization while retaining perceptual systems in
early vision sensitive to glossy surfaces (see Wada, Sakano, & Ando,
2014).
1.2. Physiological effects of experiencing outdoor scenery
While the physiological effects of viewing water outdoors in a
comparative landscape context has not been tested explicitly, there is
suggestive physiological evidence of the relaxation response while
viewing plants and trees outdoors. In one study relevant to this issue,
resting heart rate and salivary cortisol were reliably lower immediately
following “forest therapy” in which middle aged and elderly women
engaged in various tasks for nearly 5 h in a forest setting compared with
the same time frame after their usual activities the day before (Ochiai,
Song, Kobayashi et al., 2015). These women also reported feeling more
relaxed during their forest activities. Even a brief 17-min walk in a forest
compared with an urban environment can lower heart rate as well as
increase subjective ratings of relaxation (Song et al., 2015; for extensive
reviews of forest bathing research, see; Kondo, Jacoby, & South, 2018;
Payne & Delphinus, 2019; Kotera, Richardson, & Shefeld, 2020).
Sampling blood pressure and heart rate directly in the eld provides
Fig. 1. Sampling sites for measuring blood pressure and heart rate in Study 1.
Note that the swimming pool, the tree in the parking lot (center) and the small
sign over Russell Blvd. were the targets of visual xation (middle right).
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
3
a more realistic assessment of the physiological effects of viewing na-
ture. For example, both blood pressure and heart rate measured during
15-min walks and seated views of forest settings were reliable lower
than during walks and seated views of urban settings with trafc (Park
et al., 2009). A similar seated-viewing protocol was used by Ojala,
Korpela, Tyrv¨
ainen, Tiittanen, and Lanki (2019) to measure blood
pressure in participants grouped according to their urban experience.
Participant blood pressure was sampled before being seated and then
after seated participants viewed a noisy city center with pedestrians, an
urban park, and an urban woodland with conifers for 15 min. Although
blood pressure did not differ appreciably in the seated viewing condi-
tion, the less urban-oriented group participants reported feeling more
restored and relaxed in the woodland setting than in the urban park and
city. Similarly, research using seated participants comparing 15-min
periods of viewing a forest from a partially enclosed opening (curtains
on 3 sides) and being completely enclosed showed that both blood
pressure and heart rate were not reliably different between the viewing
conditions (Horiuchi et al., 2014). In contrast, the forest view decreased
frontal lobe cerebral oxygenation inferred from near-infrared spectros-
copy compared with the enclosed view that is suggestive of a relaxation
response. Like this effect on brain oxygenation, the effects of viewing
nature on emotional systems can be less transient than changes in
sympathetic arousal affecting blood pressure and heart rate. As an
example, active walking by participants for 90 min in a natural versus
urban setting, followed by measuring regional cerebral blood ow from
functional magnetic resonance imaging, revealed that the nature walk
increased neural activity in the subgenual prefrontal cortex possibly
related to an increase in mental well-being (Bratman et al., 2019).
1.3. Experimental questions
The aforementioned literature supports the theoretical construct that
viewing nature, especially water, affects subjective well-being. Viewing
water might have ecologically rewarding properties resulting from
inherent knowledge resulting from a long period of natural selection
that water availability mitigates dehydration. Such emotional relief
from this omnipresent threat might be accompanied by autonomic
indices of stress reduction.
The autonomic nervous system, balancing sympathetic and para-
sympathetic tone, plays an important role in regulating blood pressure
and heart rate under different levels of stress (Appelhans & Luecken,
2006; Balzarotti, Biassoni, Colombo, & Ciceri, 2017; Malpas, 2010; Seki,
Green, Lee, Tsunetsugu, Takayama et al., 2014). Recent neurobiological
research has identied subcortical and neocortical brain areas that could
account for changes in autonomic arousal affecting blood pressure and
heart rate as well as the subjective sense of well-being.
Flickering illumination, one salient specular property of rippling
water, can activate neurons in the supercial layers of the human su-
perior colliculus (SC) initiating eye-movement saccades (cf. Schneider &
Kastner, 2005; Walker, Mannan, Maurer, Pambakian, & Kennard, 2000).
As inferred from macaque monkeys, this phylogenetically ancient
subcortical structure receives at least 10% of the axonal projections from
retinal ganglion cells (Perry & Cowey, 1984). Electrical stimulation of
the SC and its tightly integrated circuitry with the midbrain peri-
aqueductal gray (PAG) can engender rapid increases in blood pressure
and heart rate that arguably reect their joint adaptive function in
mediating immediate defensive behavior under threatening conditions
(Bandler & Keay, 1996; Keay, Dean, & Redgrave, 1990). Relevant to
water perception, drinking activity is also associated with collicular
neuronal activity in rats (Cooper, Miya, & Mizumori, 1998) and likely
thirst awareness in primates via the ventrolateral PAG (Sewards &
Sewards, 2000). While being thirsty can engender a highly conscious
state of urgency to nd water, activity in other subcortical areas inu-
encing sympathetic arousal are less consciously perceived, such as
activation of the amygdala via the SC (Diano, Celeghin, Bagnis, &
Tamietto, 2017). The aforementioned mouthing behavior of infants with
a drinking like action inuenced by the glistening properties of shiny
plates (Coss et al., 2003) might indeed characterize unconscious acti-
vation of the SC and PAG neural circuits.
Neocortical areas that appear to inuence blood-pressure variability
are the orbitofrontal (OFC), insula, and anterior cingulate cortices.
Invasive electroencephalogram probing of patients awaiting epilepsy
surgery has documented that these areas play a role in lowering blood
pressure (Lacuey et al., 2018). Intracortical stimulation of the different
insula regions can induce sympathetic or parasympathetic regulation of
heart rate (Chouchou et al., 2018), and the dorsal anterior cingulate
cortex in particular is involved with sympathetic modulation of heart
rate (Critchley et al., 2003).
It is important to note that the orbitofrontal, insula, and anterior
cingulate cortices, notably the mid-anterior region of the OFC,
contribute to subjectively experienced emotions with pleasurable
properties (Berridge, Morten, & Kringelbach, 2015; Kuhn & Gallinat,
2012), including the taste of water by thirsty individuals (O’Doherty,
2011). Positive emotions, however, are not restricted to these neocor-
tical areas and may include neural activity within the sensory and motor
cortices (see Damasio, Damasio, & Tranel, 2013). The OFC receives
major input from primary and intermediate visual cortices via the
inferior temporal lobe (Diano et al., 2017) that respond to the saliency of
glossy surfaces (Sun, Ban, Di Luca, & Welchman, 2015; Wada et al.,
2014). In light of the aforementioned neurobiological ndings, we hy-
pothesized that viewing water would engender subtle rewarding prop-
erties reected by decreases in blood pressure and heart rate compared
with viewing urban-habitat features without water.
2. Study 1
2.1. Method
The following study protocol was approved by Human Subjects-IRB
20071576-1 from the University of California, Davis. This preliminary
study addressed the aforementioned hypothesis predicting the physio-
logical effects of viewing water by comparing an urban swimming pool
with a parking lot with trees and a distant sign on a busy street.
2.1.1. Participants
Thirty two individuals (16 men and 16 women) who were members
of the Davis Aquatic Masters swim team volunteered to participate.
Three age classes were selected for study, consisting of 6 men and 4
women between 18 and 30 years of age, 4 men and 6 women between 31
and 50 years of age, and 7 men and 5 women between 50 and 85 years of
age.
2.1.2. Study sites
The location of the study was three sites at or adjacent to the Davis
Civic Center, Davis, California (Fig. 1). These sites consisted of the
following: 1) the facility swimming pool (21.6 m long ×13.7 m wide)
with white berglass walls, which, combined with chemicals in the pool,
made the surface of the water shimmer with a pale blue-green hue; 2) a
nearby parking lot with occasional people viewed peripherally at a
distance, and 3) a location on Russell Blvd. with moderate trafc across
the street from the entrance to the Davis Civic Center.
2.1.3. Blood-pressure monitoring
Blood pressure and heart rate were measured by an auto-inated
wrist cuff (Life-Source Automatic Wrist Blood Pressure Monitor Model
UB 328 manufactured by A&D Medical, San Jose, CA) that calculated
systolic, diastolic and pulse rate using the oscillometric method. The
manufacturer reports that the accuracy of this wrist-cuff model is 2% for
blood pressure and 5% for pulse rate according to the ANSI/AAMI SP-10
1987 standard. It must be noted that automated oscillometric devices
have been found to be as accurate as good aneroid sphygmomanometer
and stethoscope tests (see Stergiou, Voutsa, Achimastos, &
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
4
Mountokalakis, 1997), and wrist devices provide more accurate mea-
surements when measuring the arms of older overweight individuals
(Mostafa et al., 2020).
2.1.4. Procedure
Participants were instructed to read and sign permission forms
before proceeding to the three locations where they were instructed to
stand still without speaking and hold his/her wrist cuff on the left arm at
heart level. Once the participant was positioned for blood-pressure
sampling, the participant was instructed to visually xate a specic
target for 1 min, following which the blood-pressure monitor was
immediately activated by the researcher (CK) standing nearby. No other
individuals were nearby during this sampling period. While the partic-
ipant maintained visual xation, blood-pressure measurement started
15 s later during the ~25-sec period of cuff deation. This device was
then removed from the participant before moving to next sampling site.
The three sampling sites were visited successively in a preselected ran-
domized order. At the swimming pool, participants stood approximately
2 m from the edge of the water and xated a spot on the water’s surface
for a 1 min 40 s following which they walked to the next sampling site.
At the parking lot, participants were instructed to xate a tree at
approximately 18-m distance for 1-min 40 s. At Russell Blvd., partici-
pants standing on the sidewalk were instructed to xate for 1 min 40 s a
triangular sign diagonal to the street at 105-m distance. Following
completions of these tasks, the blood-pressure monitor was removed and
the systolic, diastolic and heart (pulse) rates of participants were
recorded from the device’s memory. To measure any acoustical dis-
tractions, the background sound-pressure level (SPL) at each site was
measured using the A setting on the sound-pressure meter (Radio Shack
Model 33-20-50).
2.2. Results
To account for age-related variation of blood pressure in partici-
pants, the systolic score was divided by the diastolic score, yielding the
systolic/diastolic (S/D) ratio that reects conventional arterial periph-
eral resistance (Drzewiecki, Hood, & Apple, 1994; Fernberg, Roodt,
Maria Fernstr¨
om, & Hurtig-Wennl¨
of, 2019). Statistical analyses were
conducted using Statistica 4.0 (TIBCO Software Inc.). Changes in the
systolic/diastolic-ratio and heart rate following the 1-min 40 s
target-viewing period were each examined using two-factor (sex, 3 age
classes) between subjects and one-factor (3 sites) within subjects ana-
lyses of variance. To examine the specic hypothesis that viewing water
should affect these measures, planned comparisons employed tests of
simple effects to examine mean pairwise differences in these sampling
sites. Non-predicted comparisons were made post hoc to identify the
sources of interaction effects.
2.2.1. Blood pressure
The main effects for sex and age were not statistically signicant
whereas the main effect for the three sites was signicant (F(2,52) =
9.976, p =0.0002). A planned comparison using a test of simple effect,
averaged for age and sex, showed that the S/D ratio was signicantly
lower (Fig. 2A) with a large effect size (F(1, 26) =12.526, p =0.002, d =
1.4) while viewing the water in the swimming pool (M =1.400, 95% CI
±0.039) compared with viewing the tree in the parking lot (M =1.469,
95% CI ±0.046). Similarly, a test of simple effect showed that the S/D
ratio while viewing the swimming pool was signicantly lower (F(1, 26)
=19.446, p =0.0002, d =1.7) with a large effect size than when gazing
at the sign on Russell Blvd. (M =1.516, 95% CI ±0.082). This higher S/
D ratio at Russell Blvd. was nearly reliably greater than that of the
parking lot (p =0.098).
Since no hypotheses were made for sex or age effects, the following
analyses provide descriptive indices of reliability for the sources of
statistically signicant interactions. For the interaction of sex and site (F
(2,52) =4.571, p =0.015), the men were the primary source for blood-
pressure differences averaged for the three sites (F(2,52) =13.244, p =
0.0002), exhibiting a reliably higher S/D ratio than the women specif-
ically at Russell Blvd. (F(1, 26) =4.948, p =0.035). The age class by site
interaction was also signicant (F(4,52) =4.564, p =0.003). Averaged
for sex, the three sites differed reliably for participants 31–50 years of
age (F(2,52) =14.581, p =0.000009) and participants older than 51
years (F(2,52) =14.581, p =0.016). Finally, post hoc analysis of the
statistical power of the main effect comparing the three sites using
G*Power 3.1 (Faul, Erdfelder, Lang, & Buchner, 2007) yielded a power
of 1.0 that was useful for selecting the sample sizes for the next study on
the S/D ratio.
2.2.2. Heart rate
None of the main effects and interactions was statistically signicant
for heart rate. However, planned pairwise comparisons (Fig. 2B) showed
that heart rate (beats/min) was reliably slower (F(1, 26) =4.916, p =
0.035, d =0.9) while viewing the swimming pool (M =62.50, 95% CI ±
3.24) compared with viewing the sign on Russell Blvd (M =64.38, 95%
CI ±3.17).
2.3. Discussion
The results of Study 1 showed that after visually xating the water in
the swimming pool for 1 min 40 s, the S/D ratio for blood pressure was
reliably lower compared with focusing on a tree in the parking lot and a
small distant sign on Russell Blvd. Heart rate was also reliably lower
Fig. 2. Results of blood pressure (A) and heart rate (B) for Study 1. Means and
standard errors are shown.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
5
while viewing water than after viewing the sign on Russell Blvd. Thus,
the results of our study provide full support to our hypothesis that
viewing water can decrease blood pressure compared with viewing
selected urban-habitat features without water. For heart rate, however,
our hypothesis received only partial support due to the lack of a reliable
difference between viewing water and the tree in the parking lot.
It is reasonable to argue that these differences reect some special
de-arousing properties of viewing water due to its historical rewarding
ecological signicance (Coss & Moore, 1990) and perhaps the partici-
pants’ fondness of swimming. Alternatively, the more visually complex
parking lot, and especially the nosier trafc moving near the trafc sign
(68-76 dBA SPL compared with 45–47 dBA SPL near the tree and 55-57
dBA SPL at the swimming pool), might have engendered shifts of covert
(nonfoveal) attention during sign xation (see Kelley, Serences, Gies-
brecht, & Yantis, 2008; Laeng & Teodorescu, 2002) that augmented
sympathetic arousal, causing a transient increase in vasoconstriction
and increased heart rate (Appelhans & Luecken, 2006, p. 230; Malpas,
2010, p. 525; Schlader & Charkoudian, 2018).
Although not predicted specically, the elevation in sympathetic
arousal while viewing the sign on Russell Blvd. possibly illustrates the
difculty in controlling visual and acoustical distractions. Consistent
with this nding, the aspect of conducting autonomic nervous-system
research in an urban setting without laboratory control over stochasti-
cally dynamic events is daunting (cf. Gatersleben & Andrews, 2013;
Gladwell et al., 2012; Hartig, Evans, Jamner, Davis, & G¨
arling, 2003; Lee
et al., 2014; Ojala et al., 2019), but provides perhaps unique insights into
the verisimilitude of our experimental ndings.
3. Study 2
The ndings of Study 1 showed that viewing water in the swimming
pool reduced blood pressure and heart rate in comparison with the sign
on Russell Blvd., a busy street with noisy trafc; albeit, the background
trafc noise while viewing the water in the swimming pool was inter-
mediate to the other sites. The following study takes this heuristical
approach further by sampling blood pressure and heart rate in a semi-
natural arboretum setting with relatively low background noise. A
third dependent variable, subjective relaxation, was added because
participants engaged in less cognitively demanding tasks of visually
xated various water and ground-based targets of their choice. The
context for adding participant ratings of their emotional state while
viewing these targets was based on the theoretical perspective of the
James-Lange theory of emotions predicting that participants can sub-
jectively evaluate their level of relaxation based on their level of auto-
nomic activity (see Critchley, Coreld, Chandler, Mathias, & Dolan,
2000 p. 162; Damasio & Carvalho, 2013).
Reinforced by the ndings of Study 1, we predicted that, that blood
pressure and heart rate would decrease while participants viewed water
in a semi-natural setting compared with habitat features without water.
Conversely, subjective ratings of relaxation were predicted to increase
while participants viewed water compared with these habitat features
without water.
3.1. Method
While the hypothesis that viewing water modulates sympathetic tone
was maintained, represented by transient decreases in blood pressure
and heart rate, the current study sought to evaluate these effects in the
semi-natural microhabitat of a university campus arboretum charac-
terized by the varying expansiveness of a stream, trees, and open grassy
areas. Based on the results of Study 1 in which older participants
exhibited a difference in blood pressure at the three sites, this study re-
examined the same age classes. As mentioned above, an additional
dependent variable involving cognitive appraisal of affect was added to
aid interpretation of the physiological effects of viewing water. This
measure consisted of a subjective rating of relaxation.
3.1.1. Participants
Seventy three participants (37 men and 36 women) were recruited
from the University of California, Davis campus and city community.
Nearly all of the participants were familiar with the campus arboretum.
Participants agreed to participate after receiving instruction about the
study’s goals and reading the permission form. Again, three age cate-
gories were selected for study, consisting of 10 men and 14 women
between 18 and 30 years of age, 15 men and 9 women between 31 and
50 years of age, and 12 men and 13 women older than 50 years of age.
There were no medication or caffeine restrictions on participants, all of
whom were sufciently t to walk comfortably to each sampling site.
3.1.2. Study sites
Six sites with water and ground views were selected along a 1.62 km
asphalt path running alongside Putah Creek in the University of Cali-
fornia, Davis Arboretum (Fig. 3). Choice of sampling sites was based on
the distance of the path from the water and the absence of visual
obstruction of the water by vegetation. Photographs of these six sites are
shown in Figs. 4 and 5). Each site has a water and ground view. Site 1
consisted of a small lake and sloping grassy hill. Site 2 consisted of a
narrow stream and a view of a building and trees. Site 3 consisted of a
narrow stream and trees. Site 4 consisted of a wider stream and open
grassy eld. Site 5 consisted of a larger lake and open grassy eld. Site 6
consisted of murky water with oating debris and trees. Measurements
of background sounds at the six sites ranged from 45 to 50 dBA SPL
mediated by variation in distant trafc noise.
3.1.3. Procedure
The procedure for sampling blood pressure and heart rate was
identical to Study 1 with the exception that participants were sampled
twice, once while viewing the water for 1 min 40 s and once while
viewing the ground behind them at eye level for 1 min 40 s. At each of
the six sites, participants alternated in viewing the water or ground rst
in a balanced order that was randomized among participants. During a
sampling episode, each participant was positioned at a preselected
location on the path and instructed to stand still without speaking and
hold his/her wrist cuff on the left arm at heart level. The participant was
then instructed to direct her/his gaze at a selected target for 1 min,
following which the blood-pressure monitor was activated by the
researcher (CK) standing nearby. The participant maintained visual
xation on the target of her/his choice until the device was removed
from her/his wrist by CK. Immediately after each blood-pressure sam-
pling episode, participants stated how relaxed they felt while viewing
each target using a 1 to 7 unipolar scale, with 1 being “not at all relaxed”
to 7 being “completely relaxed.” Again it must be emphasized that,
unlike Study 1, participants could choose the visual targets of xation at
eye level in front of them, a property of gaze behavior analogous to
viewing something in the landscape that briey caught their attention
(see Henderson, 2003) and possible increased default brain states (see
Nagai, Critchley, Featherstone, Trimble, & Dolan, 2004; Nakashima
et al., 2015). Beginning with site 1, participants walked to each sampling
site successively along the path at a pace that did not fatigue older
participants. After the stating their relaxation score at site 6, the
blood-pressure monitor was removed and the systolic, diastolic and
heart rates of participants were recorded from the device’s memory. The
duration of entire walk, including the six successive ~3.5 min sampling
times at each site, ranged from 45 to 50 min.
Sampling was conducted over a 4-month period during the cool
morning hours of summer and early fall. At the time of day this study
was conducted in the campus arboretum, there were few disturbances
from passing pedestrian trafc and occasional bicycles. If pedestrians
approached on the pathway, blood-pressure sampling was delayed until
the pathway was clear. As such, there were no instances of people
passing in front of the participants while they viewed the water or
ground behind them.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
6
3.2. Results
Changes in the systolic/diastolic-ratio and heart rate following the 1
min 40 s target-viewing period and subjective rating of relaxation were
each examined using two-factor (sex, 3 age classes) between subjects,
two-factor (6 sites, 2 views for each site) within subjects analyses of
variance. Again, planned comparisons employed tests of simple effects
for hypothesis testing. Standardized effect sizes are reported for pairwise
comparisons of water and ground views.
3.2.1. Blood pressure
The main effects of sex and age, averaged for the 6 sampling sites and
2 views, were not statistically signicant whereas the main effect for the
six sampling sites, averaged for sex, age class, and water and ground
views, was signicant (F(5,335) =3.371, p =0.006). Because this sig-
nicant difference in sampling sites might reect walking fatigue, a post-
hoc analysis of any progressive changes in blood pressure at each site as
participants walked the 1.62 km distance, averaged for water and
ground views, revealed no signicant linear trend (p =0.785).
Relevant to hypothesis testing, the main effect comparing the water
and ground views, averaged for sex, age class, and sites was statistically
signicant with a medium effect size (F(1,67) =4.183, p =0.045, d =
0.5). The S/D ratio of viewing water, averaged for sex, age class and
sites, was M =1.417, 95% CI ±0.036 compared with M =1.480, 95% CI
±0.043 while viewing the adjacent ground. Tests of simple effects,
averaged for sex and age class, identied which sites contributed to the
main effect for the average difference in S/D ratios while viewing the
water and ground. Visually xating the water at sites 3 and 6 that are
narrow sections of **** Creek (Fig. 6A) reduced the S/D ratios signi-
cantly compared with viewing the adjacent ground with trees (respec-
tively: (F(1,67) =12.342, p =0.0008, d =0.9; F(1,67) =8.820, p =
0.0003, d =0.7).
Although the mean S/D ratios for the wider sections of Putah Creek
(sites 1, 4 and 5) that includes two lakes did not differ appreciably from
their adjacent ground views, averaged for sex and age class, post hoc
analysis averaging these wider sections of Putah Creek yielded a reliably
lower S/D ratio (F(1,67) =5.865, p =0.018, d =0.6) than the average
for the narrower sections of Putah Creek (sites 2, 3 and 6). The S/D ratio
for the more expansive sections of Putah Creek (Fig. 6B) was M =1.441,
CI 95% ±0.027 compared with M =1.482, CI 95% ±0.044 for the
narrower sections of Putah Creek (Fig. 7A). This effect on S/D ratios was
not apparent for averaging the adjacent ground views for the three wider
or narrower sections of Putah Creek (p =0.210).
The interaction of the 3 age classes and the water and ground views,
averaged for the 6 sites, was also signicant (F (2,67) =5.293, p =
0.007). A test of simple effect, averaged for sex and the 6 sites, indicated
that the primary source for this interaction was the lower S/D ratio for
male and female participants 18-30 years of age while they viewed the
water compared with the ground (F(1,67) =14.596, p =0.0003, d =
0.9).
3.2.2. Heart rate
The heart-rate measures exhibited signicant main effects for sex
and age, respectively (F(1,67) =4.933, p =0.03; F(1,67) =22.130, p =
0.0000001). Like that of blood pressure, the main effect comparing the
six sampling sites, averaged for sex and age class, was also statistically
signicant (F(5,335) =12.284, p =0.000001). However unlike the
absence of a signicant linear trend for blood pressure, averaged for
water and ground views, heart rate exhibited a signicant linear trend as
subjects walked sequentially to each sampling site F(1,67) =27.204, p
=0.0000019). The source of this linear trend, however, was restricted to
the 18-30 year-old age class that exhibited a relatively progressive in-
crease in heart rate as they walked to each sampling site (F(1,67) =
31.650, p =0.0000004).
With respect to the hypothesis for heart-rate changes, the main effect
comparing the water and ground views, averaged for sex, age class, and
Fig. 3. The progression of sampling sites along the 1.62 km path along Putah Creek (blue) in the University of California, Davis Arboretum. (For interpretation of the
references to color in this gure legend, the reader is referred to the Web version of this article.)
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
7
sites, was signicant with a medium effect size (F(1,67) =5.087, p =
0.027, d =0.6). The average heart rate (beats/min) while of viewing
water, averaged for sex, age class and sites, was M =72.790, 95% CI ±
3.73 compared with M =73.477, 95% CI ±3.58 while viewing the
adjacent ground.
A test of simple effect, averaged for sex and age class, showed that
viewing the small lake at site 1 (Fig. 6B) lowered heart rate signicantly
compared with viewing the grassy hill (F(1,67) =6.033, p =0.017, d =
0.6). Averaged for sex and age class, another test of simple effect showed
that viewing the water in the narrow section of Putah Creek (site 6)
lowered heart rate signicantly compared with viewing the nearby trees
(F(1,67) =16.494, p =0.0002, d =1.0). As was analyzed post hoc for
blood pressure, the average heart rate while viewing the three wider
sections of Putah Creek (sites 1, 4 and 5) was lower than the average
heart rate while viewing the three narrower stream sections (sites 2, 3
and 6), but this difference only approached statistical signicance (F
(1,67) =3.690, p =0.059, d =0.5).
________________________________________________________________________
3.2.3. Subjective rating of relaxation
The main effects for sex, sites, and views were statistically signicant
for the subjective ratings of relaxation. The main effect comparing
sampling sites, averaged for sex, age class and views, was signicant (F
(5,335) =30.935, p =0.00000001). Averaged for sex, age, and sites, the
main effect for mean differences in water and ground views was also
highly signicant with a large effect size (F(1,67) =37.693, p =
0.0000001, d =1.5). The average subjective rating of relaxation for
viewing the water, averaged for sex, age class and sites, was M =4.920,
95% CI ±0.332 compared with M =4.340, 95% CI ±0.325 for viewing
the ground. Tests of simple effects showed that viewing the water at four
sites was signicantly more relaxing (Fig. 8) than viewing the adjacent
ground. These sites were the small lake at site 1 (F(1,67) =22.109, p =
0.00002, d =1.1), the narrow stream at site 2 (F(1,67) =6.086, p =
0.016, d =0.6), the narrow stream at site 3 (F(1,67) =11.099, p =
0.002, d =0.8), and the larger lake at site 5 (F(1,67) =29.197, p =
0.0000009, d =1.3).
Examination of the relaxing properties of water expansiveness was
examined post hoc by averaging the relaxation scores for viewing water
at the wider sections of Putah Creek (sites 1, 4 and 5) compared with the
narrower sections (sites 2, 3 and 6). This comparison (Fig. 7B), averaged
for sex and age class, was highly signicant (F(1,67) =51.820, p =
0.0000001, d =1.8), yielding a very large effect size for the higher
rating of subjective relaxation while viewing the more expansive water
(M =5.511, 95% CI ±0.307) compared with the narrower stream
sections (M =4.329, 95% CI ±0.352). The same comparison made for
ground views adjacent to the expansive and narrow stream sections was
also found to be highly signicant (F(1,67) =59.807, p =0.0000001, d
=1.9). In this comparison, the open grassy elds (sites 1, 4 and 5) were
signicantly more relaxing to view (M =4.817, 95% CI ±0.338) than
the more visually occluded landscape with trees at sites 2, 3 and 5 (M =
3.863, 95% CI ±0.313).
The interaction of age class and views of water and ground was
Fig. 4. Views of water and adjacent ground at sampling sites 1-3. Note the narrower section of Putah Creek at site 3.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
8
statistically signicant (F(2,67) =5.176, p =0.008). Tests of simple
effects showed that participants 18–30 years of age and those over 50
years of age reported that they were signicantly more relaxed viewing
the water compared with the adjacent ground (respectively: F(1,67) =
35.389, p =0.0000001, d =1.5; (F(1,67) =11.262, p =0.001, d =0.8).
3.2.4. Association of subjective relaxation and physiological change
Follow-up exploratory analyses examined any causal associations of
subjective ratings of relaxation with blood pressure and heart rate. There
is a long history associated with the James-Lange theory of emotions
predicting that variation in autonomic activity can be interpreted as
subjective emotions (cf. Critchley et al., 2000 p. 162; Damasio & Car-
valho, 2013). Consistent with this idea, regression analyses examined
blood pressure and heart rate separately as the predictor variable and
subjective ratings of relaxation as the response variable. Higher ratings
of relaxation were negatively correlated with lower S/D ratios while
viewing water at ve of the six sites and correlated negatively at two
sites at statistically signicant levels. While viewing the small lake at site
1, which received the second highest mean rating of subjective relaxa-
tion among the sites, lower S/D ratios were negatively correlated reli-
ably with higher ratings of relaxation (r(71) = − 0.289, p =0.013). In
contrast, site 6 with murky water engendered the lowest mean rating of
relaxation and also showed a reliably negative correlation of lower S/D
ratios with higher ratings of relaxation (r(71) = − 0.319, p =0.006).
Conversely, higher heart rates were positively correlated with higher
ratings of relaxation at all six water-viewing sites. Reliable or nearly
reliably positive correlations were found for viewing the second highest-
rated small lake at site 1 (r(71) =0.226, p =0.054), the third highest-
rated wider stream at site 4 (r(71) =0.280, p =0.016), and the
highest-rated larger lake at site 5 (r(71) =0.290, p =0.013). There were
no statistically signicant correlations of S/D ratios or heart rates with
subjective relaxation ratings of relaxation for any views of the ground.
3.3. Discussion
Our research conrmed our hypothesis by documenting that viewing
water compared with viewing the adjacent ground at six successive sites
in a campus arboretum engendered reliable physiological effects
reasonably consistent with a transient relaxation response. Averaged
across sex, age, and sampling sites, the main effects for the mean S/D
ratio and heart rate were statistically signicant, with both measures
lower during the 1-min, 40-sec period of visually xating a viewer-
selected spot on the water in Putah Creek than when visually xating
a viewer-selected spot on the adjacent ground.
At specic sites, mean blood pressure at site 3 with a narrow stream
was reliably lower while the mean subjective rating of relaxation was
reliably higher. Mean heart rate at Site 1 with the small lake was reliably
lower while the mean rating of subjective relaxation was reliably higher.
Conversely, both mean blood pressure and heart rate were reliably lower
at site 6 with murky water, compared with the adjacent ground with
trees and vegetation, but this site also exhibited with lowest mean
subjective ratings of relaxation for both water and ground views. These
Fig. 5. Views of water and adjacent ground at sampling sites 4-6.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
9
low ratings for site 6 are not surprising as Smith and Davies-Colley
(1992) report that low water clarity impacts aesthetic preference and
the slope behind the trees limits the eld of view. Nevertheless, viewing
the murky water at site 6 induced reliable autonomic differences than
the ground. With respect to possible participant fatigue after walking
1.62 km to site 6, our post-hoc linear trend analyses of the sequential
sampling sites indicated that only the youngest age class showed a
reliable increase in heart rate that likely reects their faster walking
pace.
Although not predicted beforehand, post hoc analysis showed that the
three expansive sections of Putah Creek represented by two small lakes
and a wider section of the creek were more effective, on average, at
lowering the S/D ratio than the three narrower sections of the creek. Our
exploration of this effect adds additional information about the physi-
ological effects of focusing on water that encompasses a large peripheral
eld of view. This expansiveness effect is almost mirrored reliably (p =
0.059) by the lower mean heart rate while viewing the two small lakes
and a wider section of putah Creek compared with viewing the adjacent
ground. It is important to note here that visually xating viewer-selected
spots on the adjacent ground at the expansive and narrower sections of
Putah Creek showed no reliable effects for blood pressure and heart rate.
Evidence that viewing water engenders higher subjective ratings of
relaxation is apparent in the reliable main effect averaged across sex,
age, and sampling sites. As with the blood-pressure measure, viewing
the water in the more expansive sections of Putah Creek also increased
subjective ratings of relaxation compared with the narrower sections.
Fig. 6. Results of blood pressure (A) and heart rate (B) for Study 2. Means and standard errors are shown. Mean differences of visually xating the water and ground,
averaged for the six sampling sights, were statistically signicant for both physiological measures.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
10
Although not the aim of Study 2, post hoc analysis showed that partici-
pants also rated the adjacent ground next to these expansive sections of
Putah Creek reliably higher than the ground adjacent to these narrower
sections of Putah Creek. Higher ratings of relaxation while visually
xating viewer-selected spots on the ground at these sites with open
grassy space with trees in the background is consistent with landscape-
preference research using projected colored slides that document the
positive aesthetic attributes of spacious scenes with low grassy hills with
sparse trees compared with settings with closely grouped tree that ob-
structs visual access (e.g., Han, 2007; Herzog & Bryce, 2007; Herzog &
Kutzli, 2002; Hull and Buhyoff, 1983; Ruddell, Gramann, Rudis, &
Westphal, 1989; Yang & Brown, 1992).
As reected by our exploratory regression analyses, corresponding
decreases in blood pressure and increases in subjective ratings of
relaxation were found at ve of six sites, two of which yielded reliable
negative correlations. This negative association provides some insight
into the emergence of subjective sensations of feeling relaxed that co-
occurs with a drop in peripheral sympathetic activity. As discussed
above, variation in autonomic responses are thought to inuence higher
levels of cognition (Critchley, 2005). In Study 2, such decreases in S/D
ratios during directed attention at water appear to have modulated a
subtle change in an affective state subject to conscious awareness
perhaps not unlike that activated during biofeedback relaxation (see
Critchley, Melmed, Featherstone, Mathias, & Dolan, 2001). Conversely,
the positive correlations of higher heart rate and higher subjective rat-
ings of relaxation, correlated reliably at almost three of six sites, could
be interpreted as decreased parasympathetic inhibition at the vagal
branches of the autonomic nervous system thereby increasing heart rate
via sympathetic activity (see Appelhans & Luecken, 2006). Research on
the physiological properties of positive emotions indicates that, joy
(elation) is the only positive emotion that enhances sympathetic activity
(Kreibig, 2010, p. 407). As such, these positive correlations of heart rate
and subjective relaxation might reect participants’ misinterpretation of
their joy of observing the expansive sections of water with enhanced
relaxation. Supportive evidence that joy is associated with increased
heart rate is reported during green-color perception and joy imagery
(Vrana, 1993; Moharreri, Rezaei, Dabanloo, & Parvaneh, 2014). None-
theless, the interaction of parasympathetic and sympathetic inuence on
heart rate is complex and the positive correlation of heart rate and
subjective relaxation might also include a breathing artifact in which
inspiration can increase heart rate slightly (Berntson, Cacioppo, &
Quigley, 1993). Participants were not given any instructions about
monitoring their breathing during bouts of visual xation.
4. General discussion and conclusion
The theoretical stance that inspired our research on the physiological
effects of water perception was based on prior research describing
anecdotal observations of nursing age infants mouthing mirrors on toys
and experimental study of infants mouthing glossy plates on their hands
and knees like that of older children drinking from a rain pool in a
developing country (cf. Coss et al., 2003; Coss & Moore, 1990). More
direct evidence that water is attractive to crawling infants is based on
research using a Water Cliff apparatus and a sloped pathway leading to
deep water (Rodrigues de Morais, 2020). These infant studies suggest
that water perception has partially innate properties likely reecting a
long period of natural selection for water detection and investigation.
Based on attitude studies, other researchers have suggested that pref-
erence for viewing water might be an evolved property (cf. Adevi &
Grahn, 2012; Orians & Heerwagen, 1992; Ulrich, 1983, 1993).
In the current research comparing different biotic and abiotic attri-
butes, visual xation of water in outdoor settings was predicted to
engender changes in autonomic tone reected by decreasing blood
pressure and heart rate, and when explicitly asked, participant subjec-
tive ratings of relaxation. More specically, Study 1 showed that visual
xation of the swimming pool water for 1 min, 40 s lowered systolic
blood pressure approximately 10 mm Hg relative to diastolic pressure
compared with visually xating the small sign on a noisy street with
automobiles passing nearby. The estimated mean drop in systolic blood
pressure relative to diastolic pressure when viewing the swimming pool
compared with the parking lot tree was about 5 mm Hg. This decrease in
systolic blood pressure is approximately the same as the mean decrease
in systolic blood pressure while viewing the water in Putah Creek
compared with the adjacent ground. The arboretum and parking lot with
trees do share similar vegetation attributes for comparing the physio-
logical effects of viewing water; albeit, unlike the arboretum, the geo-
metric properties of the swimming pool, nearby buildings, and parked
automobiles would clearly characterize an urban setting with low visual
access.
In Study 2, participants reported higher subjective ratings of relax-
ation while viewing water that, when considered along with decreasing
blood pressure and heart rate, is suggestive of a physiologically induced
relaxation response (see Critchley et al., 2001). Nevertheless, the auto-
nomic effects of viewing water in Putah Creek were clearly transient at
each sampling site due to the experiment protocol of alternating bouts of
visually xating the water and adjacent ground for 1 min, 40 s. These
transient properties beg the question of whether these brief decreases in
blood pressure and heart rate are physiologically meaningful in a
Fig. 7. Comparison of sampling sites with more expansive sections of Putah
Creek (average of sites 1, 5, 6) with narrower sections of Putah Creek (average
of sites 2, 3, 4) for blood pressure (A) and relaxation (B). Means and standard
errors are shown.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
11
manner that would impact more systemic physiological effects beyond
transient subjective feelings of relaxation. Clearly, our protocol of
viewing water and adjacent ground with regulated intervals of visual
xation is unnatural. However in the typical context of strolling the
arboretum with periodic glances at the water, the cumulative effects of
this experience on autonomic tone might be similar to that reported by
other researchers examining walking and stationary views of nature (cf.
Park et al., 2009; Song et al., 2015). Future landscape studies conducted
outdoors could consider investigating whether sustained viewing of
water, bolstered by its partially innate perceptual properties, would
buffer the effects of visual habituation on autonomic tone.
CRediT authorship contribution statement
Richard G. Coss: Conceptualization, Methodology, Formal analysis,
Resources, Data curation, Writing – original draft, Visualization, Project
administration. Craig M. Keller: Methodology, Investigation, Data
curation, Visualization, Writing – review & editing.
Declaration of competing interest
The authors declared no potential conicts of interest with respect to
the research, authorship, and/or publication of this article.
Acknowledgement
This research was funded by Faculty Grant D922 and undergraduate
teaching support from the University of California, Davis.
References
Adevi, A. A., & Grahn, P. (2012). Preferences for landscapes: A matter of cultural
determinants or innate reexes that point to our evolutionary background?
Landscape Research, 37(1), 27–49. https://doi.org/10.1080/01426397.2011.576884
Appelhans, B. M., & Luecken, L. J. (2006). Heart rate variability as an index of regulated
emotional responding. Review of General Psychology, 10, 229–240. https://doi.org/
10.1037/1089-2680.10.3.229
Balzarotti, S., Biassoni, F., Colombo, B., & Ciceri, M. R. (2017). Cardiac vagal control as a
marker of emotion regulation in healthy adults: A review. Biological Psychology, 130,
54–66. https://doi.org/10.1016/j.biopsycho.2017.10.008
Bandler, R., & Keay, K. A. (1996). Columnar organization in the midbrain periaqueductal
gray and the integration of emotional expression. In G. Holstege, R. Bandler, &
C. E. Saper (Eds.), Progress in brain research (Vol. 107, pp. 285–300). Elsevier Science
E.V.
de Beer, Y., & van Aarde, R. J. (2008). Do landscape heterogeneity and water distribution
explain aspects of elephant home range in southern Africa’s arid savannas? Journal
of Arid Environments, 72(11), 2017–2025. https://doi.org/10.1016/j.
jaridenv.2008.07.002
Behrensmeyer, A. K., & Laporte, L. (1981). Footprints of a Pleistocene hominid in
northern Kenya. Nature, 289, 167–169. https://doi.org/10.1038/289167a0
Behrensmeyer, A. K., & Reed, K. E. (2007). Reconstructing the habitats of
Australopithecus: Paleoenvironments, site taphonomy, and faunas. In K. E. Reed,
J. G. Fleagle, & R. E. Leakey (Eds.), The paleobiology of australopithecus (pp. 41–60).
Springer.
Benson, H., Beary, J. F., & Carol, M. P. (1974). The relaxation response. Psychiatry, 37(1),
37–46. https://doi.org/10.1080/00332747.1974.11023785
Berntson, G. G., Cacioppo, J. T., & Quigley, K. S. (1993). Respiratory sinus arrhythmia:
Autonomic origins, physiological mechanisms, and psychophysiological
implications. Psychophysiology, 30(2), 183–196. https://doi.org/10.1111/j.1469-
8986.1993.tb01731.x
Berridge, K. C., Morten, L., & Kringelbach, M. L. (2015). Pleasure systems in the brain.
Neuron, 86, 646–664. https://doi.org/10.1016/j.neuron.2015.02.018
Beyer, R. M., Krapp, M., Eriksson, A., & Manica, A. (2021). Climatic windows for human
migration out of Africa in the past 300,000 years. Nature Communications, 12, 4889.
https://doi.org/10.1038/s41467-021-24779-1
Bobe, R., & Behrensmeyer, A. K. (2004). The expansion of grassland ecosystems in Africa
in relation to mammalian evolution and the origin of the genus Homo.
Palaeogeography, Palaeoclimatology, Palaeoecology, 207(3–4), 399–420. https://doi.
org/10.1016/j.palaeo.2003.09.033
Borza, L. R. (2014). Retrogenesis in AD: Evidence and implications. Psihiatru.ro, 36(1),
44–45.
Bratman, G. N., Hamilton, J. P., Hahn, K. S., Daily, G. C., Gross, J., & J, J. (2019). Nature
experience reduces rumination and subgenual prefrontal cortex activation.
Proceedings of the National Academy of Sciences, 112(28), 8567–8572. https://www.
pnas.org/cgi/doi/10.1073/pnas.1510459112.
Chouchou, F., Maugui`
ere, F., Vallayer, O., Catenoix, H., Isnard, J., Montavont, A., et al.
(2018). How the insula speaks to the heart: Cardiac responses to insular stimulation
in humans. Human Brain Mapping, 40(9), 2611–2622. https://doi.org/10.1002/
hbm.24548
Clearwater, Y. A., & Coss, R. G. (1991). Functional aesthetics to enhance well-being in
isolated and conned settings. In A. A. Harrison, Y. A. Clearwater, & C. McKay
(Eds.), The human experience in Antarctica: Applications to life in space (pp. 331–348).
New York: Springer-Verlag.
Cooper, B. G., Miya, D. Y., & Mizumori, S. J. Y. (1998). Superior colliculus and active
navigation: Role of visual and non-visual cues in controlling cellular representations
of space. Hippocampus, 8(4), 340–372. https://doi.org/10.1002/(SICI)1098-1063
(1998)8:4<340::AID-HIPO4>3.0.CO;2-L
Coss, R. G., Clearwater, Y. A., Barbour, C. G., & Towers, S. R. (1989). Functional decor in
the international space station: Body orientation cues and picture perception. NASA
Technical Memorandum. https://books.google.com/books?id=4DA2AQAAMAAJ.
Fig. 8. Results of the subjective rating of relaxation. Means and standard errors are shown.
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
12
Coss, R. G., & Moore, M. (1990). All that glistens: Water connotations in surface nishes.
Ecological Psychology, 2(4), 367–380. https://doi.org/10.1207/s15326969eco0204_3
Coss, R. G., Ruff, S., & Simms, T. (2003). All that glistens: II. The effects of reective
surface nishes on the mouthing activity of infants and toddlers. Ecological
Psychology, 15(3), 197–213. https://doi.org/10.1207/S15326969ECO1503_1
Critchley, H. D. (2005). Neural mechanisms of autonomic, affective, and cognitive
integration. The Journal of Comparative Neurology, 493(1), 154–166. https://doi.org/
10.1002/cne.20749
Critchley, H. D., Coreld, D. R., Chandler, M. P., Mathias, C. J., & Dolan, R. J. (2000).
Cerebral correlates of autonomic cardiovascular arousal: A functional neuroimaging
investigation in humans. Journal of Physiology, 523(1). https://doi.org/10.1111/
j.1469-7793.2000.t01-1-00259.x, 259–170.
Critchley, H. D., Mathias, C. J., Josephs, O., O’Doherty, J., Zanini, S., Dewar, B.-K., et al.
(2003). Human cingulate cortex and autonomic control: Converging neuroimaging
and clinical evidence. Brain, 126, 2139–2152. https://doi.org/10.1093/brain/
awg216
Critchley, H. D., Melmed, R. N., Featherstone, E., Mathias, C. J., & Dolan, R. J. (2001).
Brain activity during biofeedback relaxation: A functional neuroimaging
investigation. Brain, 124(5), 1003–1012. https://doi.org/10.1093/brain/
124.5.1003
Damasio, A., & Carvalho, G. B. (2013). The nature of feelings: Evolutionary and
neurobiological origins. Nature Reviews Neuroscience, 14, 143–152. https://doi.org/
10.1038/nrn3403
Damasio, A., Damasio, H., & Tranel, D. (2013). Persistence of feelings and sentience after
bilateral damage of the insula. Cerebral Cortex, 23(4), 833–846. https://doi.org/
10.1093/cercor/bhs077
Diano, M., Celeghin, A., Bagnis, A., & Tamietto, M. (2017). Amygdala response to
emotional stimuli without awareness: Facts and interpretations. Frontiers in
Psychology, 7, 2029. https://www.frontiersin.org/article/10.3389/fpsyg.2016.0202
9.
Drzewiecki, G., Hood, R., & Apple. (1994). Theory of the oscillometric maximum and the
systolic and diastolic detection ratios. Annals of Biomedical Engineering, 22, 88–96.
Falk, D. (1990). Brain evolution in Homo: The “radiator” theory. Behavioral and Brain
Sciences, 13, 333–381.
Faul, F., Erdfelder, E., Lang, A.-G., & Buchner, A. (2007). G*Power 3: A exible statistical
power analysis program for the social, behavioral, and biomedical sciences. Behavior
Research Methods, 39, 175–191. https://doi.org/10.3758/BF03193146
Fernberg, U., Roodt, J., Maria Fernstr¨
om, M., & Hurtig-Wennl¨
of, A. (2019). Body
composition is a strong predictor of local carotid stiffness in Swedish, young adults –
the cross sectional Lifestyle, biomarkers, and atherosclerosis study. BMC
Cardiovascular Disorders, 19, 205. https://doi.org/10.1186/s12872-019-1180-6
Gatersleben, B., & Andrews, M. (2013). When walking in nature is not restorative—the
role of prospect and refuge. Health & Place, 20, 91–101. https://doi.org/10.1016/j.
healthplace.2013.01.001
Gladwell, V. F., Brown, D. K., Barton, J. L., Tarvainen, M. P., Kuoppa, P., Pretty, J., et al.
(2012). The effects of views of nature on autonomic control. European Journal of
Applied Physiology, 112, 3379–3386. https://doi.org/10.1007/s00421-012-2318-8
Han, K.-T. (2007). Responses to six major terrestrial biomes in terms of scenic beauty,
preference, and restorativeness. Environment and Behavior, 39(4), 529–556. https://
doi.org/10.1177/0013916506292016
Hartig, T., Evans, G. W., Jamner, L. D., Davis, D. S., & G¨
arling, T. (2003). Tracking
restoration in natural and urban eld settings. Journal of Environmental Psychology,
23, 109–123. https://doi.org/10.1016/S0272-4944(02)00109-3
Hatala, K. G., Roach, N. T., Ostrofsky, K. R., Wunderlich, R. E., Dingwall, H. L.,
Villmoare, B. A., et al. (2017). Hominin track assemblages from Okote Member
deposits near Ileret, Kenya, and their implications for understanding fossil hominin
paleobiology at 1.5 Ma. Journal of Human Evolution, 112, 93–104. https://doi.org/
10.1016/j.jhevol.2017.08.013
Henderson, J. M. (2003). Human gaze control during real-world scene perception. Trends
in Cognitive Sciences, 7(11), 498–504. https://doi.org/10.1016/j.tics.2003.09.006
Herzog, T. R., & Bryce, A. G. (2007). Mystery and preference in within-forest settings.
Environment and Behavior, 39(6), 779–796. https://doi.org/10.1177/
0013916506298796
Herzog, T. R., & Kutzli, G. E. (2002). Perference and perceived danger in eld/forest
settings. Environment and Behavior, 34(6), 819–835. https://doi.org/10.1177/
001391602237250
Hess, E. H. (1975). The tell-tale eye. Van Nostrand Reinhold Company.
Horiuchi, M., Endo, J., Takayama, N., Murase, K., Nishiyama, N., Saito, H., et al. (2014).
Impact of viewing vs. not viewing a real forest on physiological and psychological
responses in the same setting. International Journal of Environmental Research and
Public Health, 11, 10883–10901. https://doi.org/10.3390/ijerph111010883
Hull, B. R., IV, Buhyoff, G. J. (1983). Distance and scenic beauty, a nonmonotonic
relationship. Environment and Behavior, 15(1), 77–91. https://doi.org/10.1177/
0013916583151004
Keay, K. A., Dean, P., & Redgrave, P. (1990). N-methyl Daspartate (NMDA) evoked
changes in blood pressure and heart rate from the rat superior colliculus.
Experimental Brain Research, 80, 148–156.
Kelley, T. A., Serences, J. T., Giesbrecht, B., & Yantis, B. (2008). Cortical Mechanisms for
shifting and holding visuospatial attention. Cerebral Cortex, 18(1), 114–125. https://
doi.org/10.1093/cercor/bhm036
Kingston, J. D., & Harrison, T. (2007). Isotopic dietary reconstructions of Pliocene
herbivores at Laetoli: Implications for early hominin paleoecology. Palaeogeography,
Palaeoclimatology, Palaeoecology, 243(3–4), 272–306. https://doi.org/10.1016/j.
palaeo.2006.08.002
Kondo, M. C., Jacoby, S. F., & South, E. C. (2018). Does spending time outdoors reduce
stress? A review of real-time stress response to outdoor environments. Health &
Place, 51, 136–150. https://doi.org/10.1016/j.healthplace.2018.03.001
Kotera, Y., Richardson, M., & Shefeld, D. (2020). Effects of Shinrin-Yoku (forest
bathing) and nature therapy on mental health: A systematic review and meta-
analysis. International Journal of Mental Health and Addiction, 20, 337–361. https://
doi.org/10.1007/s11469-020-00363-4
Kreibig, S. D. (2010). Autonomic nervous system activity in emotion: A review. Biological
Psychology, 84(3), 394–421. https://doi.org/10.1016/j.biopsycho.2010.03.010
Kuhn, S., & Gallinat, J. (2012). The neural correlates of subjective pleasantness.
NeuroImage, 61, 289–294. https://doi.org/10.1016/j.neuroimage.2012.02.065
Lacuey, N., Hampson, J. P., Theeranaew, W., Zonjy, B., Vithala, A., Hupp, N. J., et al.
(2018). Cortical structures aassociated with human blood pressure control. JAMA
Neurology, 75(2), 194–202. https://doi.org/10.1001/jamaneurol.2017.3344
Laeng, B., & Teodorescu, D.-S. (2002). Eye scanpaths during visual imagery reenact those
of perception of the same visual scene. Cognitive Science, 26(2), 207–231. https://doi.
org/10.1016/S0364-0213(01)00065-9
Lee, J., Tsunetsugu, Y., Takayama, N., Park, B. J., Li, Q., Song, C., et al. (2014). Inuence
of forest therapy on cardiovascular relaxation in young adults. Evidence-based
Complementary and Alternative Medicine, 2014(834360). https://doi.org/10.1155/
2014/834360
Ľ
ubomíra, B., & Matúˇ
s, P. (2017). The inuence of motor activity on the swimming
ability of preschool aged children. Journal of Physical Education and Sport, 17(3),
1043–1047. https://efsupit.ro/images/stories/30sept/Art%20160.pdf.
Malpas, S. C. (2010). Sympathetic nervous system overactivity and its role in the
development of cardiovascular disease. Physiological Reviews, 90, 513–557. https://
doi.org/10.1152/physrev.00007.2009
Moharreri, S., Rezaei, S., Dabanloo, N. J., & Parvaneh, S. (2014). Study of induced
emotion by color stimuli: Power spectrum analysis of heart rate variability.
Computers in Cardiology, 41, 977–980. https://ieeexplore.ieee.org/stamp/stamp.jsp?
tp=&arnumber=7043208.
Mostafa, M. M. A., Hasanin, A. M., Alhamade, F., Abdelhamid, B., Sana, A. G.,
Kasem, S. M., et al. (2020). Accuracy and trending of non-invasive oscillometric
blood pressure monitoring at the wrist in obese patients. Anaesthesia Critical Care &
Pain Medicine, 39(2), 221–227. https://doi.org/10.1016/j.accpm.2020.01.006
Nagai, Y., Critchley, H. D., Featherstone, E., Trimble, M. R., & Dolan, R. J. (2004).
Activity in ventromedial prefrontal cortex covaries with sympathetic skin
conductance level: A physiological account of a “default mode” of brain function.
NeuroImage, 222(1), 243–251. https://doi.org/10.1016/j.neuroimage.2004.01.019
Nakashima, R., Fang, Y., Hatori, Y., Hiratani, A., Matsumiya, K., Kuriki, I., et al. (2015).
Saliency-based gaze prediction based on head direction. Vision Research, 117, 59–66.
https://doi.org/10.1016/j.visres.2015.10.001
Newman, R. W. (1970). Why man is such a sweaty and thirsty naked animal: A
speculative review. Human Biology, 42(1), 12–27. https://www.jstor.org/stable/
41449001.
Ochiai, H., Ikei, H., Song, C., Kobayashi, M., Miura, T., Kagawa, T., et al. (2015).
Physiological and psychological effects of a forest therapy program on middle-aged
females. International Journal of Environmental Health and Public Health, 12(12),
15222–15232. https://doi.org/10.3390/ijerph121214984
O’Doherty, J. P. (2011). Contributions of the ventromedial prefrontal cortex to goal-
directed action selection. Annals of the New York Academy of Sciences, 1239. https://
doi.org/10.1111/j.1749-6632.2011.06290.x, 118–12.
Ojala, A., Korpela, K., Tyrv¨
ainen, L., Tiittanen, P., & Lanki, T. (2019). Restorative effects
of urban green environments and the role of urban-nature orientedness and noise
sensitivity: A eld experiment. Health & Place, 55, 59–70. https://doi.org/10.1016/j.
healthplace.2018.11.004
Orians, G. H., & Heerwagen, J. H. (1992). Evolved responses to landscapes. In
J. H. Barkow, L. Cosmides, & J. Tooby (Eds.), The adapted mind: Evolutionary
psychology and the generation of culture (pp. 555–579). New York: Oxford University
Press.
Park, B.-J., Tsunetsugu, Y., Kasetani, T., Morikawa, T., Kagawa, T., & Miyazaki, Y.
(2009). Physiological effects of forest recreation in a young conifer forest in
Hinokage Town, Japan. Silva Fennica, 43(2), 291–301. http://www.metla./silvaf
ennica/full/sf43/sf432291.pdf.
Payne, M., & Delphinus, E. (2019). The most natural of natural therapies: A review of the
health benets derived from Shinrin-Yoku (forest bathing). Advances in Integrative
Medicine, 6, S109–S110.
Perry, V., & Cowey, A. (1984). Retinal ganglion cells that project to the superior
colliculus and pretectum in the macaque monkey. Neuroscience, 12(4), 1125–1137.
https://doi.org/10.1016/0306-4522(84)90007-1
Roach, N., Hatala, K., Ostrofsky, K. R., Villmoare, B., Reeves, J. S., Du, A., et al. (2016).
Pleistocene footprints show intensive use of lake margin habitats by Homo erectus
groups. Scientic Reports, 6, 26374. https://doi.org/10.1038/srep26374
Rodrigues de Morais, C. B. (2020). Infant’s relationship with drop-offs and water
environments. Ph.D. dissertation. Australia: Edith Cowan University https://ro.ecu.
edu.au/theses/2346.
Rosinger, A. Y. (2019). Biobehavioral variation in human water needs: How adaptations,
early life environments, and the life course affect body water homeostasis. Human
Biology, 32(1), Article e23338. https://doi.org/10.1002/ajhb.23338
Ruddell, E. J., Gramann, J. H., Rudis, V., & Westphal, J. M. (1989). The psychological
utility of visual penetration in near-view forest scenic-beauty models. Environment
and Behavior, 21(4), 393–412. https://doi.org/10.1177/0013916589214002
Ruff, C. B. (1994). Morphological adaptation to climate in modern and fossil hominids.
Yearbook of Physical Anthropology, 37, 65–107. https://doi.org/10.1002/
ajpa.1330370605
R.G. Coss and C.M. Keller

Journal of Environmental Psychology 81 (2022) 101794
13
Sakakibara, M., Takeuchi, S., & Hayano, J. (1994). Effect of relaxation training on
cardiac parasympathetic tone. Psychophysiology, 31(3), 223–228. https://doi.org/
10.1111/j.1469-8986.1994.tb02210.x
Schlader, Z. J., & Charkoudian, N. (2018). Neural control of blood pressure and body
temperature during heat stress. Morgan & Claypool Publishers. https://doi.org/
10.4199/C00162ED1V01Y201805ISP081
Schneider, K. A., & Kastner, S. (2005). Visual responses of the human superior colliculus:
A high-resolution functional magnetic resonance imaging study. Journal of
Neurophysiology, 94, 2491–2503. https://doi.org/10.1152/jn.00288.2005
Scholz, F., & Kappeler, P. M. (2004). Effects of seasonal water scarcity on the ranging
behavior of Eulemur fulvus rufus. International Journal of Primatology, 25(3), 599–613.
https://doi.org/10.1023/B:IJOP.0000023577.32587.0b
Seki, A., Green, H. R., Lee, T. D., Hong, L.-S., Tan, J., Vinters, H. V., et al. (2014).
Sympathetic nerve bers in human cervical and thoracic vagus nerves. Heart Rhythm,
11(8), 1411–1417. https://doi.org/10.1016/j.hrthm.2014.04.032
Sewards, T. V., & Sewards, M. A. (2000). The awareness of thirst: Proposed neural
correlates. Consciousness and Cognition, 9, 463–487. https://doi.org/10.1006/
ccog.2000.0462
Sigg, H., & Stolba, A. (1981). Home range and daily march in a Hamadryas baboon troop.
Folia Primatologica, 36, 40–75. https://doi.org/10.1159/000156008
Smith, D. G., & Davies-Colley, R. J. (1992). Perception of water clarity and colour in
terms of suitability for recreational use. Journal of Environmental Management, 36(3),
225–235. https://doi.org/10.1016/S0301-4797(05)80136-7
Song, C., Ikei, H., Kobayashi, M., Miura, T., Taue, M., Kagawa, T., et al. (2015). Effect of
forest walking on autonomic nervous system activity in middle-aged hypertensive
individuals. International Journal of Environmental Research and Public Health, 12,
2687–2699. https://doi.org/10.3390/ijerph120302687
Spoor, F., Leakey, M. G., Gathogo, P. N., Brown, F. H., Ant´
on, S. C., McDougall, I., et al.
(2007). Implications of new early Homo fossils from Ileret, east of Lake Turkana,
Kenya. Nature, 448, 688–691. https://doi:10.1038/nature05986.
Stergiou, G. S., Voutsa, A. V., Achimastos, A. D., & Mountokalakis, T. D. (1997). Home
self-monitoring of blood pressure: Is fully automated oscillometric technique as good
as conventional stethoscopic technique? American Journal of Hypertension, 10(4),
428–433. https://doi.org/10.1016/S0895-7061(96)00402-5
Sun, H.-C., Ban, H., Di Luca, M., & Welchman, A. E. (2015). fMRI evidence for areas that
process surface gloss in the human visual cortex. Vision Research, 109, 149–157.
https://doi.org/10.1016/j.visres.2014.11.012
Taylor, A. G., Goehler, L. E., Galper, D. I., Innes, K. E., & Bourguignon, C. (2010). Top-
down and bottom-up mechanisms in mind-body medicine: Development of an
integrative framework for psychophysiological research. Explore, 6(1), 29–241.
https://doi.org/10.1016/j.explore.2009.10.004
Ulrich, R. S. (1981). Nature versus urban scenes, some psychophysiological effects.
Human Behavior and Environment, 13, 523–2556. https://doi.org/10.1177/
0013916581135001
Ulrich, R. S. (1983). Aesthetic and affective response to natural environment. In
I. Altman, & J. F. Wohlwill (Eds.), Behavior and natural environments (pp. 85–125).
New York: Plenum.
Ulrich, R. S. (1993). Biophilia, biophobia, and natural landscapes. In S. R. Kellert, &
E. O. Wilsons (Eds.), The biophilia hypothesis (pp. 73–137). Washington, DC: Island/
Shearwater.
Vrana, S. R. (1993). The psychophysiology of disgust: Differentiating negative emotional
contexts with facial EMG. Psychophysiology, 30(3), 279–286. https://doi.org/
10.1111/j.1469-8986.1993.tb03354.x
Wada, A., Sakano, Y., & Ando, H. (2014). Human cortical areas involved in perception of
surface glossiness. NeuroImage, 98, 243–257. https://doi.org/10.1016/j.
neuroimage.2014.05.001
Walker, R., Mannan, S., Maurer, D., Pambakian, A. L. M., & Kennard, C. (2000). The
oculomotor distractor effect in normal and hemianopic vision. Proceedings of the
Royal Society B: Biological Sciences, 267(1442), 431–438. https://doi.org/10.1098/
rspb.2000.1018
Wheeler, P. E. (1993). The inuence of stature and body form on hominid energy and
water budgets; a comparison of Australopithecus and early Homo physiques. Journal
of Human Evolution, 24(1), 13–28. https://doi.org/10.1006/jhev.1993.1003
Yang, B.-E., & Brown, T. J. (1992). A cross-cultural comparison of preferences for
landscape styles and landscape elements. Environment and Behavior, 24, 471–507.
https://doi.org/10.1177/0013916592244003
Yegül, F. K. (2013). Development of baths and public bathing during the Roman
Republic. In J. D. Evans (Ed.), A Companion to the Archaeology of the Roman Republic
(pp. 13–32). Blackwell Publishing Ltd.
Zagon, A. (2001). Does the vagus nerve mediate the sixth sense? Trends in Neurosciences,
24(11), 671–673. https://doi.org/10.1016/S0166-2236(00)01929-9
Zube, E. H., Pitt, D. G., & Evans, G. W. (1983). A lifespan developmental study of
landscape assessment. Journal of Environmental Psychology, 3(2), 115–128. https://
doi.org/10.1016/S0272-4944(05)80151-3
R.G. Coss and C.M. Keller