AUTOMATIC ALERTING DOES NOT SPEED LATE MOTORIC PROCESSES IN A REACTION-TIME-TASK

When an irrelevant 'accessory' stimulus is presented at about the same time as the imperative signal in a choice reaction time-task, the lat ency of the voluntary response is markedly reduced(1), The most promin ent cognitive theories agree that this effect-is attributable to a bri ef surge in arousal ('automatic alerting'), but they disagree over whe ther the facilitation is localized to a late, low-level motoric proces s(2) or to an earlier stage, the process of orienting to and then perc eptually categorizing the reaction stimulus(3,4). To lest these altern ative hypotheses, we used the onset of the lateralized readiness poten tial (a movement-related brain potential) as a temporal landmark to pa rtition mean reaction time into two time segments. The first segment i ncluded the time required to perceive the visual stimulus and decide w hich hand to react with; the second included only motoric processes. P resentation of an irrelevant acoustic stimulus shortened the first int erval but had no effect on the second. We therefore rejected the motor ic hypothesis.