The Cannon-Bard theory is a psychological theory developed by psychologists Walter Cannon and Philip Bard, which suggests that people feel emotions first and then act upon them. These actions include changes in muscular tension, perspiration, etc. The theory was formulated following the introduction of the James-Lange theory of Emotion in the late 1800s, which alternately suggested that emotion is the result of one's perception of their reaction, or "bodily change."
The Cannon-Bard theory sparked much controversy in cognitive circles due to its suggestion that there is no mechanism to emotion, and many theorists attempted to provide explanations of emotion that suggested a mechanism. One such theory was provided by Schachter & Singer's Two factor theory of emotion, in which they posited that emotion is the cognitive interpretation of a physiological response. For many, this remains the best formulation of emotion.
I see a man outside my window. I am afraid. I begin to perspire.
The Cannon-Bard Theory of Emotion is based on the premise that one reacts to a specific stimulus and experiences the corresponding emotion simultaneously. Therefore, if one is afraid of heights and is travelling to the top of a skyscraper, they are likely to experience the emotion of fear. Subsequently, the perception of this emotion (fear) influences the person's reaction to the stimulus (heights). Cannon and Bard posited that one is able to react to a stimulus only after experiencing the related emotion.
STIMULUS (Bear) --> EMOTION (Fear) --> REACTION/RESPONSE (Run Away)