Emotions are organized around 2 basic motivational systems, appetitive and defensive, that evolved from primitive neural circuits in the mammalian brain. The appetitive system is keyed for approach behavior, founded on the preservative, sexual, and nurturant reflexes that underlie pleasant affects; the defense system is keyed for withdrawal, founded on protective and escape reflexes that underlie unpleasant affects. Both systems control attentional processing: Distal engagement by motive-relevant cues prompts immobility and orienting. With greater cue proximity (e.g., predator or prey imminence), neural motor centers supercede, determining overt defensive or consummatory action. In humans, these systems determine affective expression, evaluation behavior, and physiological responses that can be related to specific functional changes in the brain. This theoretical approach is illustrated with psychophysiological and brain imagery studies in which human subjects respond to emotional picture stimuli.
Peter J. Lang is the director of the Center for the Study of Emotion and Attention at the University of Florida, Gainesville, FL 32610.