The emotional experience is a unit in a continual dialectic interaction between how the outside world is represented and how the person experiences the world. In other words, the emotional experience is the outcome of what affects the individual and how the person comprehends and represents these experiences. The emotions are subjective reactions to events in one's environment that either cause pleasure or pain and serve as motivational forces toward desired or undesired outcomes. Emotions are considered to be changes in physiological state that occur in response to something that affects the person. Physiological changes can be seen by others if they look at you directly (e.g., fear), heard with a voice change (e.g., anger) or felt in certain parts of the body (e.g., heart beating faster). Psychological changes, on the other hand, cannot be seen or felt by others, but they can be understood through speech or behavior (e.g., love). Every emotion has a physical component that can be measured through physiology (i.e., blood pressure, heart rate) and a psychological component that can be measured through self-report (i.e., feelings of warmth towards others). Emotions can be divided into four categories according to their intensity: mild, moderate, strong, and very strong. Mild emotions include happiness, sadness, surprise, and interest. These emotions do not require much energy to experience and do not last long.