Extinction of Sidman avoidance behavior by eliminating the noxious stimulus was studied in Sprague-Dawley rats with bar-pressing as the response. Each of three subjects was trained and extinguished on each of the following schedules in a different order: nondiscriminated, response-shock interval = 20 sec, shock-shock interval = 5 sec; nondiscriminated, response-shock interval = 40 sec, shock-shock interval = 5 sec; discriminated, response-white noise interval = 15 sec, noise-shock interval = 5 sec, shock-shock interval = 5 sec. Less than one 4-hr session was required for extinction for all procedures. When a warning stimulus was present, resistance to extinction increased. Subjects did not, however, respond to avoid the signal. Only small differences in extinction were found after training on different schedules with no warning signal.The maintenance of Sidman avoidance behavior when the negative reinforcer is permanently withdrawn has not been investigated. Sidman (1955) studied the extinction component of a mixed conditioning-extinction schedule. Thirty minutes of avoidance alternated with 15 min of extinction in which the shocks were withheld. The extinction periods were so short that the avoidance behavior was not modified by the extinction contingencies. Boren and Sidman (1957) and Boren, Sidman, and Herrnstein (1959) used a schedule of 3 hr of training followed by 3 hr of extinction in successive daily sessions. They did not, however, study the extinction of the behavior until responding ceased without retraining.Sheffield theorized that greater resistance to extinction would result from avoidance training with longer delay intervals. They predicted this from the consideration that non-avoidance responses performed during long pauses after the avoidance response would be followed by shock. Since behaviors associated with long periods of not responding predominate in extinction, the punishment of these behaviors would result in a larger total number of avoidance responses in extinction in spite of lower rates. The Sidman avoidance procedure can provide a test of this hypothesis.The extinction of Sidman avoidance behavior by eliminating the noxious stimulus was studied as a function of three different training conditions. The results using two delay intervals and the results with and without an exteroceptive warning stimulus were compared. METHOD SubjectsThree naive male Sprague-Dawley rats (Holtzman Co.), 60 days old at the start of the experiment, were maintained in individual cages with free access to food and water. ApparatusAn operant conditioning chamber, 9.25 by 8.50 by 7.50 in., with a single bar at the center of one end, 3 in. from the floor, was en-153 1968, 11,[153][154][155][156] NUMBER 2 (MARCH)

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Avoidance of electric shock was used to manipulate skin potential changes elicited by a simple visual stimulus. Experimental and control Ss were matched on habituation trials and yoked for 40 acquisition and 10 extinction trials. During acquisition the avoidance Ss differentiated between stimulus and non‐stimulus periods more reliably than the controls. During extinction the avoidance group produced significantly more criterion electrodermal responses, with greater magnitude of positive wave components, than the control group. Some of the problems of appropriate control procedures inherent in this design are examined in relation to these results.

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