Perception of Stressors
1. Perception of stressor(s) as such
Stress can be caused by various reasons and for easier study we have divided the different kinds of stressors into four groups. The stress reaction begins as soon as the brain interprets the information received from the sensory organs as dangerous.
If stress is caused by some change or process in our body we feel if not pain at least discomfort, but the stress reaction begins without our will, anyway. The same is true about stressors coming from the environment such as high noise or excessive heat. We do not perceive those changes as dangerous - the brain perceives them as dangerous without our consciousness being aware; we feel only the consequent discomfort. When stress is induced by real events, such as an earthquake, interpretation of perceived information may be a conscious process but it also may not.
Come to think of stressful situations we have experienced, what most of us will probably remember is that the time elapsed since the moment we had seen a danger to the moment of "stiffening" till the moment we eventually felt fear and began to think what to do is a very short one, as if everything has happened simultaneously.
If we see a person aiming a gun at us or a dead corpse in our bed we will not even reason that this is a danger: the very picture of what we see makes the brain react momentarily. Certain pictures make us panic, without even thinking about what we see. In other situations we may see a tangible threat and nonetheless think before acting. How come the brain decides that what we see is dangerous without involving a conscious evaluation?
The perception and interpretation of perceived information by the brain is still rather unclear process. It is supposed that the brain seeks familiar images in the memory, compares them and decides that what the eyes see is either dangerous or not, or "there is no matching image in memory". The latter causes stress since everything, which is new, unfamiliar to the sensory organs is automatically considered dangerous. This hypothesis is also applied as a possible explanation of intuition - the ability to make (adequate) decisions without thinking. A psychologist studying intuition suggests that the brain relates the picture of seen with similar pictures and once having found a "matching picture" remembers how that problem(the remembered one) had been tackled. Then it applies the solution used for the remembered case in the current one.
We must mention that the above explanations are only hypotheses and should not be taken for granted. The exact mechanism by which the brain recognizes a stressor as such still remains unclear.
2. Following Physiological Reaction; Thinking How to React
As soon as we see or feel something which threatens(or enjoys) us too much, in our organism a set of physiological reactions called stress begins. These reactions are "turned on" without our will; once the mind has perceived what we see or hear or remember as dangerous, the stress reaction begins and we cannot stop it by our will. Simultaneously we begin to think how to tackle the emerged threat. We shall study the physiological reactions and thinking separately, although both processes happen simultaneously and interact with each other.
suggest additional material/new interpretations on the subject