Natural environment can effectively improve cognitive and behavioral performance as well as positive emotions. It acts as a new way of compensation in the ego-depletion field. Based on the Strength Model of Self-Control and Stress-reduction Theory of natural environment, the present study depletes self-control resources by cognitive and physical task, and measures the changes of emotion states before and after viewing natural environment pictures in order to further investigate the influence of natural environment and emotional changes on self-control performance. Since previous studies suggested that watching natural environment pictures could reduce participants' negative affect and improve self-control performance, this study hopes to provide direct evidence for the mediation effect of emotion.

Methods The study consisted of two experiments, which investigated the impact of natural environment on cognitive and physical self-control respectively. Participants were asked to read and sign the informed consent form. After that, they were allocated to natural or rest condition group by drawing lots. In Experiment 1, all 64 participants were college students (n1=63; One participant did not complete the experiment due to interruption of the program, whose record was excluded). Each participant was required to perform a working memory update task. This task could deplete participants’ self-control strength. After that, there was a 6.25-minute break, participants in natural condition were presented a slideshow consisted of 25 color pictures of natural settings. While participants in rest condition were asked to look over the slideshow or just sit in the chair. Next, using Visual Analogue Scales (VAS) and Positive and Negative Affect Schedule (PANAS) to measure emotion changes, participants completed these questionnaires before and after watching natural environment pictures or resting. At the end, the participants were asked to to complete the cognitive self-control task called Visual-CCPT. In Experiment 2, all 64 participants were college students (n2=61; Three participants’ heart rates did not match the RPE index, whose records were excluded). Wall-sit task was given as the pretest of physical self-control performance. Then, participants were asked to ride power cycle, which could deplete participants’ self-control strength. The subsequent procedures were the same as in Experiment 1. Finally, participants were asked to complete the post-test measure of physical self-control performance (wall-sit task).

Results The results of Experiment 1 showed that participants in natural condition only reduced the false number in the Visual-CCPT task (p < .05. Exposing to natural environment was indirectly associated with lower false number in the Visual-CCPT task through relieving tension (β= .291, Bootstrapped CI [.026, .961]). In Experiment 2, whether participants were exposed in the natural environment or had a rest, the emotion did not have a significant change (p > .05; p > .05). Meanwhile, the performance of physical self-control did not improve after watching the slideshow of natural environment (p > .05), and the emotion did not play a mediation role.

Conclusions The study not only investigates the role of natural environment in counteracting cognitive self-control, but also includes physical self-control task, which has more practical value in daily life. In general, natural environment can counteract against cognitive ego-depletion, but it has no effect on physical self-control. Moreover, in cognitive condition, emotion can mediate the influence of watching natural environment pictures on self-control, especially through relieving tension. These findings highlight the role of Stress-reduction Theory.