Reaction times (RTs) to a photic stimulus were evaluated as a function of the interval between a flash and a click which followed at varying intervals (ranging 20-120 msec.) in a choice RT task. RT to flash was found to be a linear function of the interstimulus interval between the flash and the click. The shorter the interval, the faster the RT. With choice RT, mean responses to flash-click pairs separated by as much as 120 msec. were reliably faster than those obtained to flash presented alone. (PsycINFO Database Record (c) 2006 APA, all rights reserved)