# Manipulating Stress Responses during Spaceflight Training with Virtual Stressors
## 2 Background on Manipulating Stress in VR  
The stress response induced by a VRE is a product of the stressors employed by the simulation and the cognitive appraisal process. A stressor refers to a specific stimulus within the environment that exert perceived demands on an individual with the outcome. Examples of stressors include noise, pain, task load, ambient temperature, and time pressure [7]. Stimuli are perceived as stressors through the cognitive appraisal process, which evaluates the meaning and significance to individual wellbeing. The appraisal process has two different categories: Primary appraisal, which evaluates the relevance and congruence of a situation with regards to the individual's goals and wellbeing, and secondary appraisal, which involves the evaluation of resources and options for coping with the perceived demand [21]. While the primary and secondary appraisals may be shaped by personal and situational factors, some researchers have focused on communal stressors related to self-preservation that have a higher likelihood of being appraised as threats [24; 25]. Further, these stressors related to self-preservation are thought to be composed of underlying \"thematic\" stressor elements which may play a pivotal role in how stimuli are cognitively apprised as a stressor. Of the known stressor elements, much attention has been paid to uncontrollability and unpredictability [24; 25]. Uncontrollability manifests with situations or consequences that are outside one's control, difficult to change, and impede progress from attaining one's desired goal [26]. Unpredictability refers to the absence of knowing the conditions under which an event will occur or what an event will be like [27]. The context of the situation (information about outcome, time, stimuli, etc.) and the individual interpretation of the stimuli determine the amount that uncontrollability and unpredictability experienced. Thus, the same stressor manipulated in different contexts may have different amounts of unpredictability and uncontrollability. Aside from stressor elements, the appraisal process also needs simulations to be immersive enough to recognize a stimulus as an existential threat or challenge. One remarkable aspect of simulated VREs is that individuals tend to respond realistically to virtual simulations [28]. Furthermore, exposure to VR simulations results in a \"response-as-if-real\" even when the visual fidelity is low, and the representation of the physical reality is significantly reduced. Three concepts have been reported as strong generators of immersive simulations: place illusion, plausibility, and virtual body ownership. Place illusion is the strong sensation of being present in the space generated by the virtual reality environment, even though participants know they are not there [29; 30; 31; 32]. Plausibility is the component of presence that is the illusion that the perceived events in the virtual environment are really happening [33]. In comparison to place illusion, which is a static characteristic, plausibility is more concerned with the dynamics of events and the situation portrayed. Lastly, virtual body ownership means utilization of multisensory correlations to provide people the illusion that foreign objects are part of their body [34]. For example, when individuals with virtual hands touch a simulated spider, results show that they find that the virtual hand increased fear [35]. Insight into how to induce stress can be gained from standardized stress tests which have been used by researchers to reliably manipulate stress levels precisely and consistently in a laboratory setting. Several stress tests include public speaking, mental arithmetic, and cold-pressor [36; 37]. These stress tests aim to use the most potent stressors possible to elicit a general physiological stress response, often unrelated to the environment the individual is in. However, these lab-based stress manipulations do not involve any operationally-relevant tasks.