Cross-modal facilitation of response time (RT) is said to occur in a selective attention task when the introduction of an irrelevant sound increases the speed at which visual stimuli are detected and identified. To investigate the source of the facilitation in RT, we asked participants to rapidly identify the color of lights in the quiet and when accompanied by a pulse of noise. The resulting measures of accuracy and RT were used to derive speed-accuracy trade-off functions (SATFs) separately for the noise and the no-noise conditions. The two resulting SATFs have similar slopes and intercepts and, thus, can be treated as overlapping segments of a single function. That speeded identification of color with and without the presence of noise can be described by one SATF suggests, in turn, that cross-modal facilitation of RT represents a change in decision criterion induced by the auditory stimulus. Analogous changes in decision criteria might also underlie other measures of cross-modal interactions, such as auditory enhancement of brightness judgments.