emotion, term commonly and loosely used to denote individual, subjective feelings which dictate moods. In psychology, emotion is considered a response to stimuli that involves characteristic physiological changes—such as increase in pulse rate, rise in body temperature, greater or less activity of certain glands, change in rate of breathing—and tends in itself to motivate the individual toward further activity. Early psychological studies of emotion tried to determine whether a certain emotion arose before the action, simultaneously with it, or as a response to automatic physiological processes. In the 1960s, the Schachter-Singer theory pointed out that cognitive processes, not just physiological reactions, played a significant role in determining emotions. Robert Plutchik developed (1980) a theory showing eight primary human emotions: joy, acceptance, fear, submission, sadness, disgust, anger, and anticipation, and argued that all human emotions can be derived from these. Psychologists Sylvan Tomkins (1963) and Paul Ekman (1982) have contended that "basic" emotions can be quantified because all humans employ the same facial muscles when expressing a particular emotion. Studies done by Ekman suggest that muscular feedback from a facial expression characteristic of a certain emotion results in the experience of that emotion. Since emotions are abstract and subjective, however, they remain difficult to quantify: some theories point out that non-Western cultural groups experience emotions quite distinct from those generally seen as "basic" in the West.