Control of concurrent avoidance and appetitive behaviors by an indicator of shock proximity

Two monkeys were exposed to concurrent schedules in which every fifth response on one lever had the dual consequences of delivering food and stepping a 20-step light counter upward; responses on a second lever stepped the light downward. By responding appropriately on each lever, a ration of food could be obtained without exposure to a brief shock that occurred when the counter reached the twentieth step. Behavioral patterns of light-counter control were analyzed when the monkeys were handicapped by several types of discontinuities in the 20-step counter: (1) different sets of four consecutive lights inoperative, (2) the upper or lower 10 steps inoperative, and (3) all lights inoperative. Generally, the monkeys maintained the light in the upper five steps of the 20-step light counter if the lights immediately preceding the shock position were functional. However, when these counter positions were inoperative, subjects maintained the counter around the highest operative position. With all positions of the light counter inoperative, no systematic pattern of responding on the food and avoidance levers occurred.