Avoidance response

Abstract: A discriminative stimulus is a stimulus condition which, (1) given the momentary effectiveness of some particular type of reinforcement (2) increases the frequency of a particular type of response (3) because that stimulus condition has been correlated with an increase in the frequency with which that type of response has been followed by that type of reinforcement. Operations such as deprivation have two different effects on behavior. One is to increase the effectiveness of some object or event as reinforcement, and the other is to evoke the behavior that has in the past been followed by that object or event. "Establishing operation" is suggested as a general term for operations having these two effects. A number of situations involve what is generally assumed to be a discriminative stimulus relation, but with the third defining characteristic of the discriminative stimulus absent. Here the stimulus change functions more like an establishing operation than a discriminative stimulus, and the new term, "establishing stimulus," is suggested. There are three other possible approaches to this terminological problem, but none are entirely satisfactory.

Abstract: Two-factor theories of avoidance were conceived to explain responding in avoidance procedures that closely resemble the Pavlovian paradigm in superficial features, although differing in the fundamental contingency of reinforcement. Both typically involve an arbitrary conditioned stimulus and a trial-by-trial sequence of pairings between the conditioned and unconditioned stimuli. According to two-factor theory, the instrumental reinforcement of avoidance is based on the Pavlovian reinforcement of a drive state in the presence of the conditioned stimulus. It has been shown, however, that the presence of the conditioned stimulus is not necessary for the occurrence of avoidance responding. A procedure in which the sole effect of the avoidance response was a reduction in the average frequency of occurrence of an aversive electric shock proved to be fully adequate to maintain lever pressing in rats, thereby suggesting that not all avoidance requires two factors. Further experiments with various new procedures suggested that the conditioned stimulus may function as a discriminative stimulus for the avoidance response, rather than as a stimulus whose removal is inherently reinforcing, as two-factor theory requires. The conditioned reflex was to I. P. Pavlov (1928, pp. 59-60) the final answer to the problem of biological adaptation. As a mechanist, Pavlov sought a naturalistic explanation for everything an animal did, which had come to mean an explanation in terms of physical processes that could be isolated by the vivisectionist techniques of nineteenth-century physiology. But the behavior of many animals, for example, the dog, precluded any such simple machinery. Dogs clearly differed in what they did and seemed to know even though they might share virtually identical inheritances. The psyche of 1 Preparation of this paper, as well as the conduct of the previously unpublished experiments described herein, was supported by grants from the National Science Foundation to Harvard University. The author wishes to express thanks to P. N. Hineline for his generosity in allowing use of some of his as yet unpublished data and for help in formulating some of the notions here advanced. An early and much reduced version of this paper was presented at the 1966 meeting of the American Association for the Advancement of Science, Washington, D. C., as part of a symposium on Aversive Control. The author owes thanks to J. V. Brady for having organized the symposium and for inviting him to participate in it. To another of the participants, D. Anger, special thanks are owed for his vigorous and insightful criticisms of many of the author's theoretical ideas. the dog was, in other words, a sizable obstacle to the progress of a science of adapta

Abstract: Avoidance learning poses a challenge for reinforcement-based theories of instrumental conditioning, because once an aversive outcome is successfully avoided an individual may no longer experience extrinsic reinforcement for their behavior. One possible account for this is to propose that avoiding an aversive outcome is in itself a reward, and thus avoidance behavior is positively reinforced on each trial when the aversive outcome is successfully avoided. In the present study we aimed to test this possibility by determining whether avoidance of an aversive outcome recruits the same neural circuitry as that elicited by a reward itself. We scanned 16 human participants with functional MRI while they performed an instrumental choice task, in which on each trial they chose from one of two actions in order to either win money or else avoid losing money. Neural activity in a region previously implicated in encoding stimulus reward value, the medial orbitofrontal cortex, was found to increase, not only following receipt of reward, but also following successful avoidance of an aversive outcome. This neural signal may itself act as an intrinsic reward, thereby serving to reinforce actions during instrumental avoidance.

Abstract: Rats received electric shock that was preceded by either a warning signal, a series of signals forming an "external clock," or no signal at all. In all conditions, subjects which could avoid and/or escape shock developed less ulceration than, did yoked "helpless" animals which received exactly the same shock (through fixed electrodes wired in series) but had no control over shock. Presence or absence of a warning signal did, however, have an effect: A discrete warning signal reduced the ulceration both of subjects having control over shock and of yoked helpless subjects. A theory is proposed to explain how psychological factors determine the development of gastric ulceration in stress situations, and the present results are examined in relation to it. In 1968 I reported that rats which could avoid or escape electric shocks lost less body weight, developed fewer stomach ulcers, and showed less fear in a stressful situation (as measured by a CER test) than did rats which received exactly the same electric shocks but could not avoid or escape them (Weiss, 1968a). A previous study which had also examined the effects of coping behavior on the development of psychosomatic pathology obtained results opposite to these. Brady, Porter, Conrad, and Mason (1958), in a study which became known as the "executive" monkey experiment (Brady, 1958), found that in four pairs of monkeys, animals which could avoid electric shocks eventually developed severe gastrointestinal pathology and died, while animals which received the same electric shocks but could not perform the avoidance response developed no discernible disorders. In the 1968a paper, I discussed the possible reasons why my results were opposite to those of Brady et al. Although the studies in question were carried out on different species, and there was an unfortunate selection factor in the executive monkey experiment (i.e., the avoidance and yoked subjects were not chosen at random but, rather, a 2-4 hr. avoidance pretest was