Self-imposed timeouts during a successive discrimination : escape or stimulus change?

The purpose of the present investigation was to examine the two major theoretical explanations for subject-initiated timeout responding during a successive discrimination. Stimulus change theorists suggest that the perceptible changes in the stimulus configuration as a consequence of timeout responding serve to reinforce that responding. Escape theorists maintain that timeout responses are emitted in order to eliminate specific stimuli that have acquired aversive characteristics. Different consequences for a timeout response, varying in the amount of visual and auditory stimulus change, were arranged for six groups comprised of three pigeons each. Two tones of differing frequencies were used as stimuli in the separate components of the multiple discrimination schedule. In the S+ component, pecks on a key were required in order to obtain reinforcement; in the S- component, responses on a foot treadle were required for reinforcement. The timeout key was introduced once the auditory discrimination was well established. Timeout responses were first recorded during a baseline phase. Experimental manipulations included an extinction phase which involved eliminating reinforcement for treadle responding. This procedure was used in an attempt to increase the aversiveness of the S-. A second procedure to enhance the aversiveness of the S- was the application of shock contingent upon treadle pressing during S-. The final procedure sought to extinguish timeout responding by the elimination of its consequences. Timeout responses during baseline, treadle extinction, shock, and timeout extinction were compared. Key-peck response rates were also examined