An experiment probed the assumption of valence-instrumentality-expectancy (VIE) theory that positive (O+) and negative (O-) outcomes operate similarly in work motivation. Nine factorial combinations of O+ (+1, +2, +3) and O- (-2, -2, -3) valence factors were randomly assigned to 72 Peruvian female psychology students, 1/student. Then, from 69 outcomes rated by the S in a pretest, 2 with the valences required by the design were unbiasedly selected to describe an internship center to her weeks later. Valence ratings obtained for the center were linearly determined by O+; O- caused nonsignificant effects. Rating instability could account for pre-posttest changes in O+ valence, but O- valences increased beyond expectations. In general, O- seemed rather vulnerable to Pollyannian mechanisms. It is concluded that in the causation of motivational forces, O+ operates in the sophisticated way proposed by VIE theory, whereas O- enters categorically, with disregard for level of negativity. This explains a large body of past VIE findings and suggests a reformulated VIE equation. (41 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).