Abstract: In 2 experiments, 9 female Sprague-Dawley albino rats were shocked every 30 sec. Before the barpress response, shocks were long (2 sec); for 3 min after a response, shocks were short (0.1, 0.5, or 1 sec). When responding reduced shocks from 2 to 0.1 sec, barpressing was acquired, and the shorter the shocks the more time spent with the short-shock condition in effect. In another procedure, the duration of individual shocks following a response was controlled so that the 1st shock was as long as those before the response (2 sec), but the remaining shocks in the 3-min period were short (0.1 sec). Barpressing was maintained in some Ss and acquired in others showing that, even when delayed, a reduction in shock duration is reinforcing. These findings question the generality of a 2-factor, safety-signal interpretation of negative reinforcement. These results plus others imply that to predict responding in aversive situations it is necessary to integrate, for at least several minutes, the parameters of aversive events that follow a response. (27 ref) (PsycINFO Database Record (c) 2014 APA, all rights reserved)