Reports 5 experiments conducted with 52 paid Ss in which detection of a visual signal required information to reach a system capable of eliciting arbitrary responses required by the experimenter. Detection latencies were reduced when Ss received a cue indicating where the signal would occur. This shift in efficiency appears to be due to an alignment of the central attentional system with the pathways to be activated by the visual input. It is also possible to describe these results as being due to a reduced criterion at the expected target position. However, this ignores important constraints about the way in which expectancy improves performance. A framework involving a limited-capacity attentional mechanism seems to capture these constraints better than the more general language of criterion setting. Using this framework, it was found that attention shifts were not closely related to the saccadic eye movement system. For luminance detection, the retina appears to be equipotential with respect to attention shifts, since costs to unexpected stimuli are similar whether foveal or peripheral. (26 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)