Emotions are defined as strong, relatively uncontrolled feelings that affect our behavior. Everyone experiences a wide range of emotions. Think for a moment about a recent emotional experience. What characterized this experience? All emotional experiences tend to have several elements in common. Emotions are generally triggered by environmental events. Anger, joy and sadness are most frequently a response to a set of external events. However, internal processes, such as imagery, can also initiate emotional reactions. All emotions, as subjectively experienced and identified, appear to be associated with physiological changes. The emotions labeled as 'joy', 'fear' and 'anger' occur in conjunction with very similar physiological patterns. Current thinking leans towards accepting the primacy (首位，至高无上) of physiological changes, which are then interpreted based on environmental occurrences. For example, a sudden falling sensation will initiate physiological changes. These changes would be interpreted on the basis of the situation in which they occur: exhilaration or excitement of bungee jumping fear of falling from a ledge (岩脊). Another characteristic feature of an emotional experience is cognitive thought. Emotions generally, although not necessarily, are accompanied by thinking. The types of thoughts and our ability to think 'rationally' vary with the type and degree of emotion. Extreme emotional responses are frequently used as an explanation for inappropriate thoughts or actions: 'I was so mad I couldn't think straight.' Emotions also have associated behaviors. While the behaviors vary between individuals and within individuals across different times and situations, there are unique behaviors characteristically associated with different emotions: fear triggers fleeing responses, anger triggers striking out, grief triggers crying, and so on. Finally, and most importantly, emotions involve subjective feelings. In fact, it is the feeling component (组成部分) that is generally referred to when emotions are mentioned. Grief, joy, anger, jealousy and fear feel very different from one another. These subjectively determined feelings are the essence of emotion. While all individuals generally evaluate emotions in a consistent manner and within individuals over time, there are some individual and situational variations. For example, few people generally want to be sad or afraid, yet we all occasionally enjoy a movie or a book that scares or saddens us—or even some of the frightening rides at theme parks! If asked, we could doubtless name numerous emotions. A group of 20 or so people can generally name or describe several hundred emotions. Therefore, it is not surprising that researchers have attempted to categorize or type emotions into more manageable clusters. Plutchik lists eight basic emotional categories: fear anger joy sadness acceptance disgust expectancy surprise. According to Plutchik, all other emotions are secondary emotions and represent combinations of these basic categories. For example, delight is a combination of surprise and joy, and contempt is composed of disgust and anger. What are the elements that produce human emotions?