Responses were maintained by a variable-interval schedule of food reinforcement. At the same time, punishment was delivered following every nth response (fixed-ratio punishment). The introduction of fixed-ratio punishment produced an initial phase during which the emission of responses was positively accelerated between punishments. Eventually, the degree of positive acceleration was reduced and a uniform but reduced rate of responding emerged. Large changes in the over-all level of responding were produced by the intensity of punishment, the value of the punishment ratio, and the level of food deprivation. The uniformity of response rate between punishments was invariant in spite of these changes in over-all rate and contrary to some plausible a priori theoretical considerations. Fixed-ratio punishment also produced phenomena previously observed under continuous punishment: warm-up effect and a compensatory increase. This type of intermittent punishment produced less rapid and less complete suppression than did continuous punishment.

The introduction of a warning signal preceding shocks greatly increased the effectiveness of avoidance responding. Periods of "warm-up" at the beginning of the session were eliminated, and the number of shocks received by the subjects was greatly reduced. With response-shock interval constant, response rate increased as the interval between the response and the onset of the warning signal was shortened. The response tended to occur shortly after the onset of the warning signal regardless of the duration of these "safe" periods. A greatly elevated response rate was maintained even when the duration of the safe period was reduced to 0.3 sec. Thus, the pre-shock signal obtained nearly exclusive control of the responding and overrode the usual "temporal discrimination" of the response-shock interval.In discriminated avoidance experiments a warning signal appears a fixed duration before a scheduled shock. Responses terminate the warning signal and postpone the shock. Under these conditions avoidance behavior develops a high probability of occurrence during the signal and a low probability in its absence (Sidman, 1955;Sidman, Mason, Brady, and Thach, 1962;Graf and Bitterman, 1963). The present report describes avoidance behavior which resulted as the interval between the response and the onset of the pre-shock warning signal was systematically varied. METHOD SubjectsTwo female and one male rat, from SpragueDawley stock Holtzman strain, approximately 100 days old at the start of the experiment, were maintained on a free-feeding diet. ApparatusThe experimental space measured 12 in. by 9 in. by 8 in. Two sides were constructed of sheet metal; the back, top, and door were of clear plastic. The floor of the compartment consisted of steel rods, 3/32 in. in diameter 1This investigation was conducted at Anna State

Some stimuli, such as light and sound, may function either as discriminative or as aversive stimuli. The lower-intensity range of such stimuli is generally used to investigate the discriminative property, whereas the higher-intensity range is used to study the aversive property and little attention has been given to its discriminative property. However, one experimenter (Azrin, 1958) has shown that stimuli of such intensity as to be aversive can also function as discriminative stimuli. Azrin presented intense noise continuously during selected portions of a fixed-interval reinforcement schedule; and he found that if the noise had been temporally associated with reinforcement, responding increased during the noise. Conversely, if the noise had been associated with extinction, responding decreased.This experiment considers the discriminative property of an aversive stimulus in a somewhat different situation. Instead of being presented continuously for a period of time, the aversive stimulus is presented only after a response has occurred. This procedure is the typical punishment paradigm. The occurrence or nonoccurrence of punishment is then selectively related to reinforcement. METHOD SubjectsThree male, White Carneaux pigeons were used as subjects. They were deprived of food until their weights were 75 to 80 per cent of their free-feeding levels. Controlled feeding maintained the weights of the individual subjects within a 15-gram range during the experiment. ApparatusThe experimental chamber is essentially the same as that described-elsewhere (Ferster, 1953). The experimental space is 13 by 14 by 15 inches, and it is enclosed within a lightproof, sound-attenuating compartment. The floor of the chamber is an electrically insulated wire grid. The response was a peck on a plastic disc with a force of at least 10 grams, and reinforcement consisted of a 3-second presentation of grain from a feed magazine. All experimental conditions were programmed by standard electrical timing and switching devices located in a separate room. Responses were recorded by electrical impulse counters and a Gerbrands cumulative recorder.Punishment consisted of an electric shock delivered through electrodes implanted in the tail region of the pigeon (Azrin, 1959). Daily recordings show that the subject's resistance was approximately 900 ohms (measured with a 50-millivolt input) with a range of approximately + 100 ohms. Alternating current was delivered to the subject through a 10,000-ohm resistor for 65 ± 3 milliseconds. When shock was not being delivered, the leads were shorted together to avoid shock inductance.

Mental hospital patients were conditioned to respond at a high rate. Then an attempt was made to eliminate the response by means of a mild punishment consisting of a period of time‐out from reinforcement (response‐produced extinction). When only one response was available for obtaining the reinforcement, the mild punishment was not effective in eliminating that response. When an alternative response was also made available for obtaining the reinforcement, the mild punishment was completely effective. It appears that even very mild punishment may be effective if the over‐all frequency of reinforcement can be maintained by means of an alternative unpunished response.

Punishment and escape were studied simultaneously by allowing a subject to escape from a stimulus situation in which responses were punished, into a stimulus situation in which responses were not punished. The frequency of the punished responses was found to be an inverse function of the intensity of punishment, whereas the frequency of the escape response was a direct function of the intensity of punishment. Both of these functions were obtained under three different schedules of food reinforcement. The strength of the escape behavior was evidenced by (1) the emergence of the escape response even when the frequency of foodl reinforcement decreased as a consequence of the escape response, (2) the maintenance of the escape response by fixed-interval and fixed-ratio schedules of escape reinforcement, and (3) the occurrence of escape responses at intensities of punishment that otherwise produced only mild suppression of the punished response when no escape was possible. This last finding indicates that a subject may be driven out of a situation involving punishment even though the punishment is relatively ineffective in suppressing the punished responses when no escape is possible.Aversive stimuli have been defined in several ways. One defining characteristic (Dinsmoor, 1954;Keller and Schoenfeld, 1950;Skinner, 1953;Holland and Skinner, 1961) is whether escape or avoidance conditioning results from the termination or postponement of the stimulus. A second defining characteristic is whether suppression results when responses produce the stimulus (Keller and Schoenfeld, 1950; Azrin and Holz, in press). This latter procedure is designated as punishment. The present experiment attempts to study both defining characteristics simultaneously. The same theoretical objective was pursued by Hefferline (1950) and Harrison and Abelson (1959) utilizing two components (bar-press and bar-release) of the same general response. The present study used two different responses to achieve greater independence: one response produced the aversive stimulus, a second avoided it. In order to establish motivation for producing the aversive stimulus, Ss were first conditioned to respond for food; then, the aversive stimulus was delivered for each ' The punishing stimulus was a brief 100 msec pulse of 60 cps ac (lelivere(I through a 1OK ohm series resistance to gold wires implanted beneath the skin and anchored around the pubis bone on each side of the bird (Azrin, 1959a). When the punishment procedure was used, the shock was delivered immediately after each response. Results Figure 1 shows the typical change in escape responses for one S as a function of the punishment intensity. It can be seen that less than three escape responses were emitted daily by this S when the punishment intensity was less than 40 v. At a critical intensity (40 v for this S, but 20 to 50 v for the other five), the escape responses increased to 60 per session (one escape response per reinforcement) and remained at that level as the intensity was increased further to 7...