The James-Lange Theory and the Cannon-Bard Theory are both theories of human emotion.
The James-Lange Theory of Emotion was developed in the nineteenth century by William James and Carl Lange. They theorized that the automatic nervous system creates physiological events like muscular tension, rise in heart rate, perspiration, and dryness of mouth which then lead to an emotional response. A good example of this theory would be: a growling dog (stimulus) leading to fast heart rate and breathing (perception of physiological changes) which leads to fear or the idea of being afraid (identification of emotion). This theory since has been disapproved by the field and challenged by others like Cannon and Bard in the 1920’s but has not been further developed.
The Cannon-Bard Theory of Emotion was developed in the twentieth century by physiologists Walter Cannon and Philip Bard. In contrast to the James-Lange Theory, the Cannon-Bard Theory suggests that emotions occur simultaneously with physiological responses. In other words, an individual experiences an emotion and the body immediately responds physiologically (i.e., muscular tension, perspiration, increased heart-rate, etc.).
The Cannon-Bard Theory argues that emotions occur in response to stimuli and are processed and responded to physiologically. The James-Lange Theory, on the other hand, suggests that the autonomic nervous system detects physiological changes, thus leading to an emotional response.