The speeding of voluntary reaction by a warning signal.

Warning signals can shorten reaction time (RT) via either a top-down mechanism, temporal attention, or a bottom-up one, phasic arousal. The goal of this review article is to identify the locus at which these processes influence RT. Electrophysiological and behavioral evidence indicate that the chronometric locus for both modulatory effects lies mainly within a narrow window at the center of the stimulus-response interval. This interval presumably encompasses late perceptual, response selection, and early motor processes. Phasic arousal is theorized to reduce the threshold for response selection within a circuit involving the supramarginal gyrus. A blind-sight study indicates that conscious, cortical level processing is necessary for temporal attention, at least when the warning signal is visual.