Motivation and emotion/Book/2013/Green exercise and emotion
What is the effect of green exercise on emotion and why?
Overview[edit | edit source]
Research has demonstrated that being in nature and exercising both have a positive impact on our mental health. In recent years psychologists have sought to find out whether being in natural environment and exercising at the same time yields synergistic benefits. This chapter reviews the evidence for the benefits of green exercise provided by psychology research.
What is green exercise?[edit | edit source]
Broadly speaking, green exercise refers to physical activity undertaken while exposed to nature. Bushwalking, Qi Gong in an urban park, mountain biking or jogging by the lake, are all examples of green exercise. Green exercise is a topic of broad interdisciplinary interest. Work in this area comes from disciplines like urban planning, health policy, architecture and design, human ecology, occupational therapy, and environmental management. Psychology has made considerable contribution to the understanding of the effects of green exercise. Psychological research findings have wide ranging relevance from the individual level to the societal level.
While green exercise is generally thought to be outdoors, it is not necessarily. Taking the lead from Pretty (2004) we can identify three levels of engagement with nature that can be used to broaden the definition of green exercise: Being in the presence of nature, viewing nature, and actively participating in nature.
So, counter-intuitively, green exercise does not have to be limited to outdoor exercise, or even to what we would conventionally call “exercise”- it can include working out on a treadmill while looking at a terrarium or a garden, and it can include activities like gardening.
What is emotion?[edit | edit source]
How would you define emotion?[edit | edit source]
Despite being so deeply ingrained in our everyday experience emotion is difficult to define, describe and explain
Feeling and mood are closely related psychological concepts that we tend to understand as synonyms for emotion. Within psychology these are distinguished from each other (though dialectically related).
Emotions are responses to significant events. A significant event may be external or internal (such as a thought, physical sensation or memory). Emotions can be thought of as multidimensional phenomena involving aspects of subjective experience (feeling), physiological arousal, expression and sense of purpose (urge) which are all dialectically related (Reeve, 2009).
Feelings[edit | edit source]
In this model, feelings constitute a component of emotion. Feeling refers to our inner psychological experience of the emotion and includes judgments, interpretations and other cognitions as well as our embodied experience of an emotion (Reeve, 2009).
Affect[edit | edit source]
While we can name a wide range of distinct (but related) feelings and emotions, affect is more or less good or more of less bad. Psychologists measure both positive affect (PA) and negative affect (NA). PA and NA are not dichotomous but appear to be independent of each other and are measured separately. It seems counterintuitive but research suggests we can we experience, for example, low levels of both NA and PA simultaneously (Diener & Emmons, 1984).
Affect is sometime referred to as mood. Affect differs from emotion in a number of ways. Emotions are short lived and intense- lasting only up to a few minutes, whereas affect is more enduring and subtle- lasting hours, days or even weeks! (Ekman, 1994a as cited in Reeve, 2009).
While emotions are responses to an event (internal or external), moods often have mysterious causes (Goldsmith, 1994 as cited in Reeve, 2009)- how often do we say things like “I don’t know what is wrong with me, I’m just in a grumpy mood today”? Emotions also differ from mood in they involve action impulses and directly influence behavior. Mood on the other hand has more direct influence over our cognition (Davidson, 1994 as cited in Reeve, 2009).
What is emotional well-being?[edit | edit source]
Emotional well-being is an aspect of our overall quality of life or subjective well being (SWB). Most of us have an intuitive sense of what well-being is. It seems quite obvious really- well-being is a sense of “being well”. However, in the context of psychological research psychological well being is a complex theoretical concept made up of a number of different elements. Subjective Well-Being can include things like positive memories, the ratio of positive and negative affect, meaningfulness, optimism and how we evaluate different aspects of our lives (Eid & Larson, 2008). SWB includes 1) cognitive components, i.e. how we think about and evaluate our lives and 2) affective components – our emotional and affective experience (Eid & Larson, 2008).
Some researchers have proposed that cognitive components of well-being remain relatively stable over adulthood and may be more difficult to change than the emotional components which tend to be responsive and dynamic (Eid & Larson, 2008).
There is a wide range of scales used to measure aspects of what we understand broadly as “well-being”. Research in to green exercise and emotion measures a wide range of related by distinct variables – some of the most common are positive and negative affect, self-esteem and anxiety.
Consider again the multi dimensional nature of emotion- where in this picture could we intervene? In mainstream psychology, changing how you think is often considered the most effective way to change how you feel. Cognitive Behavioural Therapy is the most commonly used psychological therapy and reflects this cognitive approach to emotion.
But what if we could ‘hijack’ our physiology and subconscious responses to stimuli to change our mood? Exercise and being in “nature” may be two effective ways of doing just that. As for doing both at the same time? Read on…
Excercise and emotional well-being[edit | edit source]
There is a considerable body of research looking at the psychological benefits of excercise. The positive effects of both regular and 'acute' exercise on mood and anxiety are well documented (Arent, Landers & Etnier, 2000; Reed & Buck, 2009; Reed & Ones, 2004; Petruzzello, Landers, Hatfield, Kubitz & Salazar, 1991). Overall it is thought that there are positive mental health benefits of exercise, however findings are not homogenous and different aspects of psychological well-being respond differently to exercise. There are also many factors thought to moderate the positive effects of exercise- company, competitive vs. non-competitive, duration and intensity, baseline fitness, etc. There is no consensus on the mechanisms by which exercise improves mental health. Researchers have attempted to explain the positive effects of exercise on emotion with reference to its role in fulfilling a fundamental psychological need for mastery and self efficacy; its role as a distraction; as an indirectly fulfilling social needs (in the context of sport); and due to neurophysiological changes relating to endorphins and monamines (Peluso & de Andrade (2005).
"Nature" and emotional well-being[edit | edit source]
Nature and emotion has also received attention as a subject for psychological inquiry. The over arching hypothesis of research in this area is that humans are genetically predisposed to respond psychologically and physiologically to natural environments in ways that reflect our evolutionary roots. There is evidence to suggest that responses to "natural" environments do differ significantly from our response to more artificial environments. Research into green exercise has largely derived from this field of research. Attention Resotration Theory (Kaplan & Kaplan, 1989), Biophillia (Wilson, 1984) and the work of R.S. Ulrich are influential in both environment and emotion, and green exercise and emotion
Does combining exercise and exposure to nature have a synergistic effect?[edit | edit source]
Mental health benefits of EXERCISE + mental health benefits of NATURE= more mental health benefits from GREEN EXERCISE?
Green exercise vs. excercise[edit | edit source]
Pretty, Peacock, Sellens and Griffin (2005) exposed groups of 20 people to four different sequences of images while they ran on a treadmill. One group was exposed to images that had been previously coded as “pleasant rural”, another group to “unpleasant rural”, another to “pleasant urban”, and another to “unpleasant urban”. One control group ran on a treadmill without being exposed to any images. They measure blood pressure, self-esteem and mood before and after exercise. While there was significant effect on blood pressure, self esteem and most mood measure in all groups, the greatest effect was demonstrated in both of the “pleasant” conditions. Interestingly, both the unpleasant scenes had a depressive effect on self esteem- participants in this group showed less improvement in measure than the control group. Also surprisingly in regard to mood, rural unpleasant was more depressive than urban unpleasant. Pretty et al.(2005) concluded that this finding suggests that seeing nature under threat negatively effects our mood.
Johansson, Hartig and Staats (2011) examined the psychological benefits of walking in four conditions: in a park or street, both alone and in company. Walking, per sae did overall reduce anxiety, anger and time pressure and also increased revitalization, tranquility and positive engagement. Walks in the park decreased feelings of time pressure significantly more than walks in streets. There were similar but non- significant effects for tranquility. Interesting social context moderated some of these effects such that people experienced more revitalization walking alone in a park, but more revitalization when walking in company in the street.
These results mirror findings of an earlier study (Staats & Hartig, 2004) in which having the company of a friend increased the attractiveness of a walk in and street setting, but not of a walk in a forest. In both studies, walking in a street alone was the least attractive.
The evidence for the added benefits of green exercise is not unanimous and it appears that different constructs within the broad vernacular of “emotional well-being” may respond differently. In a study assessing the effects of green exercise on UK school children Reed, Wood, Barton, Pretty, Cohen and Sandercock (2013) found no significant differences in self-esteem after exercise in rural (“green”) area and exercise in urban conditions. One interesting finding was that in the ‘green’ condition less active children did not perceive their exertion as high as in the urban condition- suggesting potential for green exercise to engage less active children in exercise.
A systematic review of studies assessing the different effects of exercise in indoor vs outdoor natural environments found that most trials reported that exercise in natural environments was associated with greater increases in revitalization, positive engagement, energy greater, enjoyment and intent to repeat the activity later; and with greater decreases in confusions, anger, depression (Coon, Boddy, Stein, Whear, Barton, Depledge, 2011). However the authors were cautious of overstating these effects and extrapolating them to broad conclusions due to the poor quality of data.
Green exercise vs. just bein' in the green[edit | edit source]
There is surprisingly little research examining this question directly.
Do different 'kinds' of green exercise have different effects on well-being?[edit | edit source]
Green exercise research has been criticized for not differentiating kinds of environments within the broad category of ‘green’ or ‘natural’. There is now a growing body of research into variables that may moderate the effects of green exercise- and not just environmental variables. Moderating factors being explored in green exercise research generally fall in to one of three categories a) different kinds of environments b) different kinds of exercise and c) different kinds of people.
Environmental variables[edit | edit source]
- Degree of (perceived) Naturalness
Mackay and Neill (2010) developed a likert scale to measure perceived naturalness of the environment. The scale ranged from 100% artificial to 100% natural. Their findings suggest that there is a greater reduction in state anxiety following exercise in environments people perceived as ‘more natural’.
- Tended vs. wild
Martens, Gutscher & Bauer (2011) compared the effects of tended vs. wild forest. The study found that there was both a stronger increase in positive affect and stronger decrease in negative affect after walking in a tended forest compared to a wild forest. These findings supported results form Herzog, Maguire and Nebel (2003) that tended green space is especially restorative. Furthermore this effect was not related to how attractive participants found the different conditions. With reference to Mackay and Neill’s (2010) use of the perceived naturalness measure it would be interesting to see what the relationship between the constructs of “perceived naturalness” and “perceived attractiveness” is.
- Outdoor vs. ‘virtual’ or visual
Thomas Plante has led some interesting work on the role virtual reality may make in enhancing the psychological benefits of indoor exercise. Plante, Sage, Clements & Stover (2006) compared well being measures before and after participation in one of three experimental conditions. In one condition, participants walked a predetermined route around a university campus. In the second condition, participants walked briskly on a treadmill while footage of the same walk around campus was projected in front of them. In condition three, participants sat in an armchair and watched the footage. While the outdoor condition was considered more enjoyable the indoor virtual reality condition showed greater decrease in tension. While both exercise conditions were energizing, the outdoor condition was the most energizing. These results suggest that there are significant differences between exercising while being outdoors and exercising while being exposed to images of the outdoors. See below for discussion of the visual bias in green exercise research.
- Role of water
White, Smith, Humphryes, Pahl, Snelling, Depledge (2010) measured perceived restorativeness and affect in response to images of natural and built up areas with and without water (“blue space”). Image (both natural and built) that included water stimulated significant increases in positive affect and were rated higher in perceived restorativeness. There was no significant difference in ratings between built up spaces containing water and “green” spaces containing water. While this study was not concerned with exercise the findings are highly relevant to green exercise research. The recognition of ‘blue space” adds to the overall elucidation of distinct elements in environments that may exert specific kinds of effects. These findings were supported by Coon et. al (2011).
Exercise variables[edit | edit source]
Researchers have sought to understand the optimal ‘dose’ of green exercise. What is the optimal duration and intensity of exercise required to induce positive psychological effects?
Barton and Pretty (2010) analysed data from 10 green exercise studies in the UK showed that the greatest change in both self-esteem and mood occurred after just 5 minutes of green exercise! This is in fairly stark contrast to the (non green) exercise research that reports durations of at least 20 minutes being optimal (Hansen, Stevens & Coast, 2001; Petuzzello et.al.m 1991).
Barton and pretty (2010) also found that for self-esteem, light intensity exercise produced the largest positive effect. The effect tapered off with increased intensity. For mood, both light and vigorous intensity seems to yield greater benefits than moderate intensity. However research on optimal intensity even for (non green) exercise is not conclusive. Considering that “dose” research relating to (non green) exercise is well in advance of green exercise research and still has no definitive answer as to optimal intensity it is likely that there will be a while before we know for sure the best dose of green exercise is.
Measuring intensity primarily enables the comparison of different kinds of exercise. It is possible that different activities have different effects despite being of the same intensity. Green exercise research has mostly involved walking or running (Coon, Boddy, Stein. Whear a& Depledge, 2011; Reed, Wood, Barton, Pretty, Cohen & Sandercock, 2013; Martens, Gutscher & Bauer, 2011; Pretty, Peacock, Sellens & Griffin, 2005). However other kinds of exercise have been examined including road cycling, orienteering, mountain biking & boxercise (Mackay & Neill, 2010) and gardening, fishing, boating, horse riding, farming activities and sailing (Barton & Pretty, 2010).
Individual differences and demographic variables[edit | edit source]
There is some evidence to suggest that the greatest increases in self-esteem after green exercise occurred in young people and the least change in older people (Barton & Pretty, 2010). Though Reed et.al. (2013) research did not show significant changes in self esteem in children after green exercise compared to non green exercise.In relation to mood, the least change was seen in young and old (Barton and Pretty, 2010).
- Baseline Mental Health
Some research also suggests that the greatest self-esteem benefits may be seen in people living with mental illness (Barton and Pretty, 2010).
- Need for restoration
Martens et al. hypothesised that the greater the need a person had for restoration (the more fatigued they were) the greater the effect would be in their well-being. This was not supported. However, Staats and Hartig (2004) found that the preference for walking in an natural environment when people imagined themselves as attentionally fatigued was double that when people imagined themselves as alert. This supported earlier findings from Staats, Kieviet and Hartig (2003). With company
Other variables[edit | edit source]
- Cognitive engagement
Duvall (2011) has provided some evidence that cognitive engagement tasks may enhance the psychological benefits of outdoor walking.
- Social context
Following work in the field of exercise and mental health social context has been examined as a moderating factor in green exercise. In the same study mentioned above, Staats and Hartig (2004) reported interesting associations between company in natural and urban environments.
In urban settings the prospect of walking with company was much more attractive to people than without company and this effect was strongest when people imagined themselves being alert and not fatigued- i.e. when they had a low need for restoration. In natural settings, company only made the prospect of walking more attractive and restorative if it added to a sense of safety. If safety was not of concerned a walk in nature alone was considered the most restorative. Johansson, Haritg and Staats (2011) find similar results for the effect of company on green exercise.
The effects of green exercise on emotion are not uniform[edit | edit source]
The following factors are thought to play a role in moderating effects
There are likely to be many more!
Theoretical influences in green exercise research[edit | edit source]
One would expect that the theoretical frameworks for green exercise research would be derived from, on the one hand, theories of exercise and psychological well-being and on the other hand theories of ‘nature’ and psychological well being. However, the latter overwhelmingly dominate and the former are all but absent. In particular one or two closely related approaches to environmental psychology underpin majority of green exercise research.
Attention Restoration Theory[edit | edit source]
(Kaplan and Kaplan 1989) dominates the theoretical landscape of green exercise research. The premise of Attention Restoration Theory (ART) is that in our day to day goal directed and task oriented lives we are continually exerting effort to voluntarily direct our attention. This ability to voluntary attend becomes fatigued over time. The counterpart to voluntary attention is involuntary or non-directed attention. Involuntary attention serves to restore the mind from attention fatigue. Certain elements environments facilitate non-directed attention- these environments are called restorative environments. ART proposes that the following environment elements are necessary for restoration- ‘fascination’, ‘being away’, ‘extent’ and ‘compatibility’.
- Fascination is involuntary attention. When we are fascinated in this sense we do not need to put in effort to ‘pay attention’. Rather we are “intrinsically compelled” but what we are attending to (Kaplan, 1995).
- Being away refers to a shift in attention. Kaplan (1995) uses the analogy of a holiday or a break, but says that this sense of being away can come from something as simple as a shift in gaze, or a conceptual shift.
- Extent refers to the ‘wholeness’ of the environment. An environment has extent when it is cohesive and rich enough to be experienced as a “different world” (Kaplan, 1995).
- Compatibility of an environment is the extent to which it fits with ones purposes. Is the environment conducive to relaxation? Or would it more likely get in the way?
These elements are all necessary for an environment to be ‘restorative’. Natural environments are not the only restorative environments but Kaplan and Kaplan (1989) suggest natural places are much more likely to be restorative than ‘unnatural’ ones.
Envrionmental aesthetics[edit | edit source]
The field of environmental aesthetics is concerned with how humans respond to visual attributes of environments. In addition, our psychological and psychobiological response to environments are thought to be adaptive, partly genetic and have evolutionary origins. The integration of what may be considered different approaches are integrated in the influential work of R.S. Ulrich and his psychophysiological stress recovery theory.
R.S Ulrich has done considerable research into the effects of different landscapes on psychological well being, the experience of pain, recovery from illness, stress response (Ulirch, 1983; Ulrich, 1984; Ulrich, Simons, Losito, Fiorito, Miles & Zelson, 1991).
The questions Ulrich asked in “Visual Landscapes and Psychological well being” in 1979 are still highly relevant and only partially addressed- particularly in the context of green exercise research.
“To what extent do the results apply to people of different ages, levels of education, culture, etc? Do the differences which characterise psychological response to nature and urban views vary seasonally? How do people respond to scenes containing water? Are nature views more therapeutic than urban scenes for individuals experiencing boredom and understimulation rather than anxiety and high arousal? Is a scene's aesthetic value related to its influence on emotional well‐being? What man‐made forms, textures, and materials evoke responses similar to those to nature elements? These and other unresolved questions underline the fact that the general issue of differential human response to nature and built elements is of central importance to landscape research and planning.”
Limitations[edit | edit source]
Notwithstanding centuries of folk wisdom about the holistic benefits of outdoor activity, green exercise is a relatively new “health” concept and a recent topic of psychological research. As such, there are a number of theoretical and methodological limitations that will no doubt be overcome with time.
While the data slowly builds the theoretical and conceptual approaches to the topic have remained fairly static. Few published articles articulate an integrated theoretical framework for understanding green exercise. The over reliance and ongoing legacy of ART and environmental psychology has meant that research is designed with certain theoretical assumptions that are quite particular and not particularly robust- the “visual bias" is a case in point.
Visual bias[edit | edit source]
The benefits of green exercise have, somewhat ironically, come from people in laboratories looking at images .The limitations inherent in this have not gone unnoticed by key researchers (Ulrich et. al, 1991) but continue to be reproduced. Being in “nature” is obviously a poly-sensory experience and it is highly likely that the experiences cannot be reduced to ‘looking at’ nature. It is possible that images may be a valid as the real thing in relation to some dimensions of our experience, but not others i.e. being in or looking at might not make any difference to our perception of ‘restorativeness’ but may make a difference to our heart rate for example.
Green exercise vs exercise bias[edit | edit source]
The research in this area tends to compare green exercise with non- green exercise. As mentioned above, comparisons between green exercise and “just being green” are few and far between. If we are to truly answer the question of whether green exercise has a synergistic effect we need to look at it from both sides.
Terms[edit | edit source]
There are also complexities around the use of language that reflect conceptual problems. “Nature” is a highly contested term- especially in the social sciences and arguably obfuscates the political and cultural dimensions of this kind of research. Notice how the terms “green” and “natural” are treated as synonyms? This slippage can be criticised not only for being illogical (because deserts are equally “natural”) but also somewhat Eurocentric. More research into the role culture plays in environmental preferences and associated emotional response is needed. There is also a related need for more sophisticated elucidation of types and elements of environments.
Methodological limitations[edit | edit source]
A relatively recent meta-analysis of green exercise and psychological well-being conducted by Coon et. al (2011) led the authors to decry the paucity of quality evidence. This is despite some of the same limitations being acknowledged repeatedly over years of research. Lack of consistent measures made comparisons difficult, as did the small sample sizes of most studies. Coon et. al. (2011) called for larger, longer studies involving populations most likely to benefit from green exercise. Pretty and Barton (2010), in their meta-analysis, called for longitudinal multi-cohort studies.
Integrating green exercise evidence into practice[edit | edit source]
Based solely on the evidence presented here, you may not become an evangelical green exerciser- the evidence isn’t unambiguously positive but it is promising! Keep in mind this area of research is in its relative infancy and also that psychology cannot paint the picture alone. There is certainly enough evidence of its benefits to give green exercise a go!
Experiment with yourself![edit | edit source]
Think outside the box[edit | edit source]
Conclusion[edit | edit source]
It is quite possible that the folks who will experience the biggest benefits are folks who are depressed and anxious. If you are struggling with depression there is a fair chance somebody has tried to drag you to some kind of exercise. In the depths of depression a 40 min slow walk can seem like a very difficult and overwhelming task. We all know we should exercise but "should" is not a very helpful word. But what about 10 mins? 5 mins? Even a walk around the back yard is likely to have some effect and its likely to feel more manageable- just show up and let your evolutionary brain and the trees do what they do!
References[edit | edit source]
Coon, J.T, Boddy, K., Stein, K., Whear, R., Barton, J. & Depledge, M.H. (2011) ‘Does participating in physical activity in outdoor natural environment have a greater effect on physical and mental well-being that physical activity indoors? A systematic review.’ Env. Sci. Technol. 45 (5), 1761.
Eid and Larsen (2008) The Science of Subjective Well Being, Guilford Press. Hansen, C. J., Stevens, L. C., & Coast, J. R. (2001). Exercise duration and mood state: How much is enough to feel better?. Health Psychology, 20(4), 267.
Herzog, T. R., Maguire, P., & Nebel, M. B. (2003). Assessing the restorative components of environments. Journal of Environmental Psychology, 23(2), 159-170.
Hug, S.M., Hartig, M., Hansmann, R., Seeland, K. & Hornung, R. (2009) ‘Restorative qualities of indoor and outdoor exercise settings as predictors of exercise frequency’ Health & Place. 15, 971-980.
Johannsson, ., Hartig, T., & Staats, H. (2011) ‘Psychological benefits of walking: moderation by company and outdoor environment’ Applied Psychology, Health and Well-Being. 3(3), 261-280.
Kaplan, R., & Kaplan, S. (1989). The experience of nature: A psychological perspective. CUP Archive.
Kaplan, S. (1995) ‘The restorative benefits of nature: toward and integrative framework’. Journal of Environmental Psychology. 15, 169-182.
Mackay, G.J. & Neill, J.T (2010) ‘The effect of “green exercise” on state anxiety and the role of exercise duration, intensity and greenness: A quasi-experimental study.’ Psychology of Sport and Exercise. 11, 238-245. Martens, D., Gutscher, H. & Bauer, N. (2011) ‘Walking in “wild” and “tended” urban forests: the impact on psychological well-being’. Journal of Environmental Psychology. 31, 36-44.
Peluso, Marco Aurélio Monteiro, and Laura Helena Silveira Guerra de Andrade. ‘Physical activity and mental health: the association between exercise and mood.’ Clinics 60.(1), 61-70.
Petruzzello, s., Landers, D.M., Hatfield, B.D., Kubitz, K.A, & Salazar, W. (1992) ‘A mete-analysis on the anxiety-reducing effects of acute and chronic exercise: outcomes and mechanisms.’ Sport Medicine. 11(3), 143-182
Plante, T.G., Cage, C., Clements, S., & Stoves, A. (2006) ‘Psychological benefits of exercise paired with virtual reality: outdoor energizes whereas indoor virtual exercise relaxes’ International Journal of Stress Management. 13(1), 108-117.
Pretty, J. (2004) ‘How nature contributes to mental and physical health.’ Spirituality and health Int.5 (2):68- 78
Pretty, J., Peacock, J., Sellens, M., & Griffin, M. (2005) ‘The mental and physical health outcomes of green exercise.’ International Journal of Environmental Health Research. 15(5), 319-337.
Reed, J., & Buck, S. (2009). The effect of regular aerobic exercise on positive-activated affect: a meta-analysis. Psychology of Sport and Exercise, 10(6), 581-594.
Reed, J., & Ones, D. S. (2006). The effect of acute aerobic exercise on positive activated affect: A meta-analysis. Psychology of Sport and Exercise, 7(5), 477-514.
Reed, K., Wood, C., Barton, J., Pretty, J., Cohen, D. & Sandercock, G. (2013) ‘A repeated measures experiment of green exercise to improve self-esteem in UK school children’. PLOSone. 8 (7) e69176 Reeve, J. (2009) Understanding Motivation and Emotion 5th Edition. John Wiley & Sons Inc. USA.
Staats, H. & Hartig, T. (2004) ‘Alone or with a friend: A social context for psychological restoration and environmental preferences’ Journal of Environmental Psychology. 24, 199-211.
Staats, H., Kieviet, A., & Hartig, T. (2003) ‘Where to recover from attentional fatigue: An expectancy-value analysis of environmental preference.’ Journal of Environmental Psychology. 23, 147-157.
Ulrich, R. S. (1979). Visual landscapes and psychological well‐being. Landscape research, 4(1), 17-23.
Ulrich, R. S. (1983). Aesthetic and affective response to natural environment. In Behavior and the natural environment. 85-125. Springer US.
Ulrich, R. S. (1984). View through a window may influence recovery from surgery. Science, 224 (4647), 420-421.
Ulrich, R. S., Simons, R. F., Losito, B. D., Fiorito, E., Miles, M. A., & Zelson, M. (1991). Stress recovery during exposure to natural and urban environments. Journal of environmental psychology, 11(3), 201-230.
White, M., Smith, A., Humphryes, K., Pahl, S., Snelling, D. & Depledge, M. (2010) ‘Blue space: The importance of water for preference, affect, and restorativeness ratings of natural and built scenes. Journal of Environmental Psychology. 30, 482-493. Wilson, E.O. (1984) Biophillia Harvard University Press.