The attention literature distinguishes two general mechanisms by which attention can benefit performance: gain (or resource) models and orienting (or switching) models. In gain models, processing efficiency is a function of a spatial distribution of capacity or resources; in orienting models, an attentional spotlight must be aligned with the stimulus location, and processing efficiency is a function of when this occurs. Although they involve different processing mechanisms, these models are difficult to distinguish empirically. We compared performance with abrupt-onset and no-onset Gabor patch stimuli in a cued detection task in which we obtained distributions of reaction time (RT) and accuracy as a function of stimulus contrast. In comparison to abrupt-onset stimuli, RTs to miscued no-onset stimuli were increased and accuracy was reduced. Modeling the data with the integrated system model of Philip L. Smith and Roger Ratcliff (2009) provided evidence for reallocation of processing resources during the course of a trial, consistent with an orienting account. Our results support a view of attention in which processing efficiency depends on a dynamic spatiotemporal distribution of resources that has both gain and orienting properties. (Contains 7 tables, 11 figures and 3 figures.)