Bradley, M.M., Codispoti, M., Cuthbert, B.N., & Lang, P.J. (2001). Emotion and motivation: Defensive and appetitive reactions in picture processing. Emotion, 1 (3), 276-298.

Abstract: Emotional reactions are organized by underlying motivational states–defensive and appetitive–that have evolved to promote the survival of individuals and species. Affective responses were measured while participants viewed pictures with varied emotional and neutral content. Consistent with the motivational hypothesis, reports of the strongest emotional arousal, largest skin conductance responses, most pronounced cardiac deceleration, and greatest modulation of the startle reflex occurred when participants viewed pictures depicting threat, violent death, and erotica. Moreover, reflex modulation and conductance change varied with arousal, whereas facial patterns were content specific. The findings suggest that affective responses serve different functions–mobilization for action, attention, and social communication–and reflect the motivational system that is engaged, its intensity of activation, and the specific emotional context. (PsycINFO Database Record (c) 2004 APA, all rights reserved)(journal abstract)