Two experiments with humans determined whether reduced conditioning following pre-exposure to the conditioned stimulus could be explained by conditioned inhibition (Experiment 1 [E1]) or extinction of responding that the conditioned stimulus (CS) might elicit during pre-exposure (Experiment 2 [E2]). In a video game task (Nelson et al., 2014), participants learned to respond to lights that signaled attacking spaceships. In E1, a red light was either pre-exposed or not pre exposed between groups prior to conditioning with a green light. Summation tests of red combined with green produced no evidence of conditioned inhibition. In E2, participants received either no pre-exposure to the light, exposure in the same context in which the conditioning would occur, or exposure in a different context. These conditions were factorially combined with whether the light and spaceship were similar (same color) or dissimilar (different colors). In the similar conditions, the light elicited weak responding during pre-exposure, which extinguished. Such extinction did not occur in the dissimilar conditions. Conditioning occurred more rapidly in the similar conditions than in the dissimilar ones, but both conditions showed an equivalent context dependent pre-exposure effect. Pre-exposure reduced conditioning regardless of whether it reduced responding prior to conditioning. The data are consistent with animal research (Lubow et al., 1968) showing no relation between responding during pre-exposure and the effects of stimulus pre-exposure. Theories which account for the effects of stimulus pre-exposure are discussed, with the conclusion that the data are most consistent with the ideas presented by Wagner (1981).