ON THE AUTOMATICITY OF IPSILATERAL RESPONSE ACTIVATION IN THE SIMON EFFECT

The effects on performance of unattended stimulus-response spatial rel ationships in choice reaction time tasks (i.e., the Simon effect) have been attributed to automatic activation of the response ipsilateral t o stimulus location. We tested this assumption using the lateralized r eadiness potential (LRP). The response key labels changed randomly fro m trial to trial and were presented either 400 Ins before (immediate-r eaction trials) or 400 ms after (delayed-reaction trials) stimulus. Th e critical lest for the automatic activation hypothesis was on delayed -reaction trials, in which LRP deflections were expected in the interv al between stimulus and response-key labels. Contrary to this predicti on. there were no LRP signs of response activation within that interva l.