Memory load and event rate control sensitivity decrements in sustained attention.

The capacity to sustain attention at an efficient level deteriorates over time in discrimination and monitoring tasks. This "vigilance decrement" results from a decrement in perceptual sensitivity only if (i) target discrimination loads memory and (ii) stimulus events occur rapidly; otherwise, the decrement reflects temporal changes in response criteria. These results provide a basis for distinguishing between the perceptual and response processes underlying the vigilance decrement that may be generalized across a range of tasks.