Effects of Signalled and Unsignalled Electric-Shock Delivery on Schedule-Controlled and Schedule-Induced Behavior

Abstract

In Experiments 1 and 2, food pellets were delivered under a fixed-interval (Fi) 40-sec. schedule, with water freely available in an operant chamber. After acquisition of stable levels of lever pressing and schedule-induced water intake, electric shock was introduced under a variable-time (Vt) 70-sec. schedule. Each of four rats was studied under signalled and unsignalled electric shock. During signalled shock delivery, a 10-sec. stimulus preceded each shock. During unsignalled shock delivery, the preshock stimulus was not presented. More suppression of lever pressing was found for all of the animals during unsignalled than signalled shock. Three of four animals also suppressed schedule-induced licking more during unsignalled than signalled shock. For both lever pressing and licking, response suppression was a function of the intensity of shock. Depending upon the intensity of shock, responding was (a) relatively unaffected during signalled and unsignalled shock, (b) suppressed primarily during unsignalled shock, or (c) markedly suppressed under signalled as well as unsignalled shock. In Experiment 3, food pellets were delivered under a fixed-time (Ft) 40-sec. schedule. Schedule-induced licking was studied under signalled and unsignalled Vt 70-sec. shock delivery. More suppression of schedule-induced licking occurred during unsignalled than signalled shock for all of the animals. These data show that schedule-induced licking, like food-maintained lever pressing, is suppressed more by unsignalled than by signalled shock delivery.