The role of conditioned stimulus termination in short-latency avoidance responding in cats

The behavioral effects of two procedures for bar-pressing avoidance training in cats were studied. In one procedure conditioned stimulus (CS) termination was response-contingent on both shock and non-shock trials; in the other the minimal duration of the CS was equal to the CS-US (unconditioned stimulus) interval. When avoidance responses did not terminate the CS short-latency avoidance responses were not acquired, the cats made more intertrial responses, and removal of the proreal and orbital gyri interfered more with avoidance responding than was observed in the other group. Abolition of shock application and introduction of a fixed duration of the CS resulted in extinction of the avoidance responses, which was more rapid in cats trained under the response contingent CS termination procedure. The data suggest that responses performed during the CS-US interval should be divided into two subclasses: short-latency responses which not only avoid pain but also avoid fear conditioned to the CS, and long-latency responses which avoid pain and escape from the fear state.