The effect of spatial cues on visual sensitivity.

Although once doubted, a consensus has emerged from the literature that visual sensitivity can be heightened locally with an appropriate precue. Experiments with partially and totally valid precues suggest an increase in sensitivity of less than one-half log unit at the precued position, as compared with other positions. New experiments with non-informative precues demonstrate that most of this small enhancement is not due to focal attention. Sensitivity can be heightened at eight positions simultaneously, just as much as when a single position is precued. Sensitivities produced by single, totally valid precues and single, non-informative precues were similar. Thus there seems to be no capacity limit for the effect of precues on visual sensitivity.