An aversive stimulus can be generally defined as one which maintains some behavior of an organism which reduces or removes the aversive stimulus. This is in contrast to positive reinforcement where the production of the stimulus is the reinforcing event. In both cases, however, some response is maintained because it changes the environment. In the simplest experimental paradigm where a response can be maintained with an aversive stimulus, a rat is placed on an electrified grid and the electric shock is turned off for a period of time whenever the rat presses a lever. The termination of the electric shock is the reinforcing stimulus, analogous with positive reinforcement in the delivery of a pellet in the case of a food deprived rat. Aversive stimuli usually involve extreme ranges, such as body trauma of various kinds, extremes of temperature above and below the normal range, and loud noises. The school yard bully reinforces the response, "Uncle," by releasing pressure on the arm of his victim; putting one's fingers in one's ears is reinforced by the reduction in extreme noise levels; clamping the nostrils shut is reinforced by termination of an extremely noxious odor; spitting a bitter substance out of the mouth is reinforced by its removal from the mouth; and withdrawing the hand from a hot surface is reinforced by the termination of the extreme temperature on the hand. A unique feature of aversive control is that once the escape or avoidance behavior is in the organism's repertoire the behavior maintained by terminating the aversive stimulus may be strengthened immediately just by presenting the aversive stimulus. The maximum reinforcing potential of the termination of the aversive stimulus is achieved instantly when it is applied. It is probably for this reason that aversive control is such a prevalent technic of behavioral control despite some of its unfortunate by-products and, frequently, long-term ineffectiveness. When the child who reaches for the candy is seized firmly and his arm or hand squeezed until he draws away or drops the candy, the instant effect of the aversive stimulus in strengthening the required escape behavior provides immediate reinforcement for the adult's behavior. Whether this form of control is to the best interests of both parties is open to question, however, and the relevant factors, including the secondary effects of the aversive control, will be discussed later. In contrast with aversive control, much positively reinforced behavior, except when a powerful generalized reinforcer is operating, can be strengthened only if the relevant deprivation conditions are in effect. Food, for example, is a reinforcer only if the organism has not eaten for some time.
Aversive Stimuli In Human Behavior
Most of the aversive stimuli mentioned above will reinforce behavior without any special history of conditioning such as occurs in the development of conditioned and generalized positive reinforcers. The removal of these aversive stimuli is reinforcing because of the phylogenetic history of the species. The most prevalent aversive stimuli in human behavior, however, are of another sort, deriving their aversive properties from the discontinuation or withdrawal of positive reinforcement. Examples of this kind of control in human behavior include fines or incarceration by governmental agencies, disapproval or criticism by individuals, ostracism, anger, dismissal from employment, or nonresponsiveness in social interactions. All of these situations function as aversive events because they are all occasions on which significant elements of an individual's repertoire will not produce their characteristic reinforcements. The withdrawal of money, as in a fine, represents, behaviorally, a change in the individual's environment in which behaviors which may normally be reinforced by spending the money can no longer be reinforced. Incarceration is an extreme form of aversive control because it prevents by physical restraint the reinforcement of nearly all of the significant and potentially strongly reinforced elements in an individual's repertoire. The child who is sent to his room cannot play with toys, take food from the refrigerator, or run outside with his friends. An individual who frowns, criticizes, or shows anger is unlikely to provide positive consequences, certainly considerably less likely than one who is smiling. The angry or critical man is, in general, considerably indisposed to provide positive reinforcers and especially in respect to the individual who is related to his anger or criticism. Ostracism is, perhaps, the most extreme form of aversive control because nearly all of the major reinforcers maintaining most individuals' behavior are mediated through the behavior of a second individual. Without the attention of the members of the community in which an individual lives, he is literally devoid of most of the behavior which is normally strong in his repertoire and which normally occurs with high frequency.
Even where human behavior is controlled by corporal punishment, as with the parent who spanks a child, the effective aversive stimulus may be the discontinuation of positive reinforcement rather than the direct deleterious effect of the corporal punishment. The parent who is disposed to punish a child is also indisposed to reinforce, and the act of corporal punishment is correlated with the loss of conditioned reinforcers such as smiling, approval, affection, all of which tend to be necessary occasions for the reinforcement of other important items in the child's repertoire. The parent may even test the effects of corporal punishment by spanking the child vigorously but doing it in a playful manner as in a game, smiling and indicating in every way that there is no disapproval of any aspect of the child's behavior. Under these conditions, most children may be spanked with sufficient force to sting the hand without any reaction from the child other than mild surprise and small confusion as to what the game is all about. The same or even lesser degrees of corporal punishment administered on other occasions will produce crying, fear, and even strong anxiety.
The correlation between the disposition to punish and the indisposition to reinforce is not inevitable and one may find, occasionally, parents whose disposition to reinforce increases after punishment rather than decreases. In this case, the effect of the punishment would stand in an entirely different relation to the repertoire, serving as a conditioned positive reinforcer instead of an aversive event because the parent's anger and corporal punishment is the occasion on which the parent now provides very favorable consequences for the child. In such a case, we might find the child emitting performances which are maintained because they produce parental anger and punishment.
THE ARBITRARINESS OF THE FORM OF THE AVERSIVE STIMULUS IN HUMAN BEHAVIOR Because the aversiveness of many of the stimuli which have been discussed above derives from the reinforcement contingencies associated with them, the actual form of the aversive stimulus is quite arbitrary. In general in a given culture there is a certain amount of consistency in respect to when reinforcements are more or less likely. Smiling individuals are inclined to reinforce; frowning individuals are not. The correlation, however, is not inevitable, and almost any form of a stimulus may be correlated with practically any condition or reinforcement. As an extreme example consider a social situation, such as a poker game, in which all of the usual correlations between behavioral dispositions and facial and postural features are distorted. A smile on a player's face might in fact constitute an aversive stimulus if the player smiles because he has a good poker hand. In this case, the smile is a stimulus in the presence of which betting behavior is not likely to be reinforced, and, in fact, likely to be punished. Persons in authority very often smile and assume a genial manner when they criticise or withdraw reinforcing behavior. Because smiling and a genial manner are customarily correlated with the positive reinforcement, the aversive effect of withdrawing the reinforcers may be considerably attenuated. Ultimately, however, the aversively controlled person will distinguish between the stimuli correlated with actual reinforcement conditions and those which are irrelevant. The administrator continues this practice because he usually does not need to be concerned with the long-term effects of his behavior and because of the large number of people he deals with for only short periods of time.
Nonsocial Aversive Stimuli
Some kinds of aversive control are essentially nonsocial, as when there is a chain of behaviors in which a series of performances are required, each providing the conditions for the next, as in the construction of a machine or the assembly of an automobile motor. In these cases, the aversive stimulus constitutes going back to the beginning of the chain. For example, when the machinist breaks a component in the assembly of a device, he must go back to the lathe to remake it. This kind of aversive control was discussed in the previous chapter in the example of the machinist whose work involved a chain of operations leading to a completed part. In these cases there is a natural contingency in which the aversive stimulus occurs because the form of a response is inappropriate to the conditions which permit completing the chain.
AVERSIVE CONTROL IN ANIMALS BY DISCONTINUING REINFORCEMENT Animal experiments contribute to our understanding of some of the basic properties of discontinuation of positive reinforcement as an aversive stimulus. To establish this kind of aversive control in an animal, first, two stimuli are provided for the animal, one of which is correlated with an extremely favorable condition of reinforcement and the other with extremely unfavorable conditions, such as extinction or very infrequent reinforcement. Once the animal's behavior comes under the control of the two stimuli, as a result of the differential reinforcement contingencies in them, the stimulus correlated with the unfavorable condition of reinforcement may be used as an aversive event.
For example, when the color of the key at which the bird pecks is green, the food is delivered every 60 seconds on the average. Periodically, however, the key turns red for 15 minutes during which no responses are reinforced. Once the bird's rate of responding falls to near zero in the red, we can punish the bird at any time when he is in the green by changing the color of the key from green to red. With such a technic, the aversive stimulus can then be delivered instantly and will be specifically contingent upon any aspect of the animal's performance. The stimulus correlated with nonreinforcement, the red key, is functionally comparable to the human examples mentioned above such as criticisms and fines, which are also events designating a situation in which the conditions of reinforcement are unfavorable. Criticism, for example, serves an analogous function to the red light in the pigeon example because a listener who criticises is functionally one who is not disposed to reinforce the speaker by basing his verbal responses on those of the speaker.
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