As described previously, the mobilization of our stress response involves the integration of multiple organs and glands controlling both the nervous and endocrine systems. Ideally, these systems communicate and coordinate to make sure that our bodies are aroused enough to effectively deal with challenges but not so aroused that we become hyper-aroused or otherwise experience incapacitating anxiety. However, this balancing act is a tricky business, and the body and brain don't always get it right.
Physiological arousal is necessary to prime our bodies for taking action. As we become more aroused in response to stressors, our alertness increases and our attention sharpens. We become increasingly focused on the stressor itself, while other aspects of the environment fade into the background. A narrowed focus of attention towards a threat is typically adaptive, as it allows us to quickly eliminate some of the available responses we might otherwise make. This decreases the likelihood that we will become overwhelmed by choices at a critical time, and allows us (ideally) to choose the best option. For instance, we can quickly move from six possible choices (which could take a substantial amount of time to sort through in our minds) to two (fight or flee). On the other hand, too much arousal may narrow our focus so drastically that we overlook the best options.
It is helpful to visualize the relationship between our level of arousal and our subsequent performance as the upside-down "U" shaped curve attributable to research performed by psychologists Robert Yerkes and J. D. Dodson (often called the "Yerkes-Dodson Curve").
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As the diagram suggests, increasing levels of arousal initially improve performance, but there quickly comes a point of diminishing returns. At high levels of stress, performance ability declines dramatically.
Arousal levels are influenced by multiple factors, including: the amount of mental energy a demand requires, our baseline level of anxiety (e.g., how anxious we are in general; sometimes referred to as our level of 'trait' anxiety), and our level of anticipatory anxiety (how worried we are in advance of an upcoming event).
Stressful activities that require more concentration will seem overwhelming much sooner than activities we are skilled at and can do without almost automatically. In sports, for example, running is considered a relatively simple activity because it normally doesn't require much conscious thought. Stress seems to improve running performance for a long period of time before a decline sets in. Other activities, like swinging a golf club, are more complex because they require a good deal of conscious thought. In this case, stress results in a much earlier decline in performance.
Each person's trait or baseline level of anxiety creates their 'zone of optimal performance under stress.' These zones vary from individual to individual; some of us begin a task with higher level of arousal than others, quickly reach our optimal zone and experience an early performance decline. Others take longer to reach their optimal zone, and don't show performance deficits (or enhancements) for a longer period of time. In other words, people are closer to tipping over to the right side of the upside down U diagram above (and experiencing decreased performance) when they start with more arousal to begin with. In contrast, people who start out with a relatively low level of arousal and respond to the pressure by getting pumped up may stay in their optimal zone of performance for longer periods of time, or at least experience the benefits of that zone when it is most needed.
Our degree of stress and subsequent arousal is also affected by our level of anticipatory anxiety. While most of us worry about the our ability to perform well in stressful situations and recognize the possibility of failure, some of us worry more than others. People will typically experience more anxiety if they anticipate a negative outcome occurring rather than a positive one. Also, the less confidence people have in their abilities, the more likely it is that they will have their performance ability disrupted by stress.
Interestingly, people who worry may actually perform better initially, but they are not able to maintain peak levels for long and their performance deteriorates rapidly. This occurs frequently in very high stress emergency situations. For instance, when some anxious people are involved in a car accident, their anxiety may escalate rapidly to the point where they cannot easily give the police officer their name and address. In such a situation, stress will have pushed them past their point of optimal performance.