Studied aggression in the form of shock setting in a competitive reaction time task. Numbered lights either indicated that shocks set by an opponent increased from mild to intense across trials or indicated a moderate setting on all trials. Within each of these 2 conditions, the actual shock intensity, which the 48 male undergraduates received on 1/2 of the trials, either increased across trials or remained constant. S's shock settings for the opponent increased across trials in the light-increasing conditions but remained constant in the light-constant conditions. Actual shock intensity had no effect on the S's shock settings. Symbolic attack, or specifically the perceived intent of the attacker, appeared to be a more potent instigator of aggression than physical attack per se. (PsycINFO Database Record (c) 2016 APA, all rights reserved)