Respondent Aggression

When two organisms are placed in the same setting and painful stimuli are delivered, the organisms may attack one another (Ulrich, Wolff, & Azrin, 1964). The fighting generated by this circumstance is called respondent aggression (or pain-elicited aggression) because it follows the presentation of aversive events. Attack occurs even though neither individual is responsible for the delivery of the painful stimuli. Ulrich and Azrin (1962) placed two rats in an operant chamber and noted that the animals showed no signs of aggression. However, when the rats were shocked, they turned and attacked each other. Elicited aggression has been documented in several species including humans (Azrin, Hutchinson, & Hake, 1963; Hutchinson, 1977), and it has been found with painful stimuli other than electric shock (Azrin, Hake, & Hutchinson, 1965). Most people recognize that they are more prone to aggression when exposed to painful stimuli. When feeling good you may never shout at your boyfriend, but you may do so if you have a severe toothache. It is probably good advice to stay clear of your boss when he or she has a headache, and so on.

O'Kelly and Steckle (1939) first described pain-elicited aggression. In these early experiments, rats were placed in a small enclosure and electric shock occurred periodically, no matter what the animals did (a procedure similar to the one that induces learned helplessness, but two rats are placed in the chamber). When the rats were periodically shocked, they began to fight. Twenty-three years later, Ulrich and Azrin (1962) systematically investigated the fighting behavior of rats to inescapable and intermittent aversive stimulation. These researchers began by testing whether two rats would fight when simply placed in a small operant chamber. They noted that the animals did not usually attack one another when placed in a confined space. However, when random shocks were given, the animals would immediately stand up and vigorously strike and bite one another (see Fig. 6.8).

Shocks were delivered at increasing frequencies, and the number of attacks increased as more and more shocks were presented. In addition, Ulrich and Azrin (1962) found that the probability of attack for any single shock increased as the number of shocks went up. When the animals got one shock every 10 min, attack followed approximately 50% of the shocks. When the animals received 38 shocks a minute, fighting followed 85% of the shocks.

Further experiments conducted by Ulrich and Azrin (1962) examined the effects of shock intensity on aggressive behavior. As shock intensity increased in milliamperes (mA), from 0.5 to 2.0 mA, the number of aggressive episodes went up. When shock intensity exceeded 2.0 mA, fighting decreased because the high-intensity shocks elicited running, jumping, and so on—responses that were incompatible with fighting.

An important question is whether such fighting occurs when animals are able to escape, or avoid, the electric shock. The floor of the operant chamber was made of metal rods,

FIG. 6.8. Two rats in the attack position induced by electric shock. Note: From "Reflexive Fighting in Response to Aversive Stimulation," by R. E. Ulrich and N. H. Azrin, 1962, Journal of the Experimental Analysis of Behavior, 5, pp. 511-520, reprinted with permission. Copyright 1962, the Society for the Experimental Analysis of Behavior, Inc.

and some of these were electrically charged positive, and others were charged with negative voltage. Animals could evade the shocks by standing on two positive or two negative rods. The rats readily learned this response, and since they did not get shocked, they did not fight. That is, allowing the animals to escape the shocks effectively eliminated the aggression.

Ulrich and Azrin (1962) varied the size of the operant chamber in another experiment. When there was little floor space (0.25 sq ft), almost all shocks resulted in fighting. As floor space increased to 2.25 sq ft, the chances of attack for any one shock decreased. It seems that the size of the chamber regulated pain-elicited fighting through the changing proximity of the opponents. In other words, the closer the animals were to each other, the greater the chances of attack attributable to shock.

To determine whether these findings occurred in other species, the researchers placed different animals in the shock box. Hamsters also fought when shocked, and these attacks occurred at shock intensities that did not elicit aggression in rats. One possibility is that hamsters have less padding or more pain receptors on their feet, making them more susceptible to low levels of shock. In contrast, mature guinea pigs would not fight when shocked. This passive response even occurred when a guinea pig was placed in the shock box with a rat. The rat attacked the guinea pig when it was shocked, but the guinea pig "reacted only by withdrawing from the rat's biting attacks following the shock delivery" (Ulrich & Azrin, 1962, p. 517). These findings suggest that there are species differences in the tendency to fight when exposed to painful stimulation.

There are other limitations on pain-elicited aggression. Ulrich and Azrin (1962) found that rats fought when exposed to intense heat or shock, but not to intense noise or cold temperature. Apparently there are specific forms of painful stimulation that elicit attack in a given species. Presumably, the type and intensity of painful stimulation that triggers attack is not the same for different kinds of animals.

Painful stimulation also produces attack-like responses in both humans and monkeys (Azrin et al., 1966; Azrin, Hutchinson, & Sallery, 1964; Hutchinson, 1977). In one experiment, squirrel monkeys were strapped into a small test chamber, and electric shock was delivered to the animals' tails (Azrin et al., 1964). As with rats, attack was elicited by electric shocks. The animals attacked other monkeys, rats, mice, and inanimate objects such as a stuffed doll, round ball, and a rubber hose that they could bite. As shock intensity increased, so did the probability and duration of the attacks—a result that parallels the findings with rats.

In a review of the side effects of aversive control, Hutchinson (1977) described bite reactions by humans to aversive stimulation. Subjects were paid volunteers who were given inescapable loud noise at regular intervals. Because the noise was delivered on a predictable basis, the subjects came to discriminate the onset of the aversive stimulus. Unobtrusive measures indicated that humans would show aggressive responses (or more precisely bite on a rubber hose) following the presentation of loud noise. The humans' responses to noise parallel the elicited fighting found in monkeys and other animals. However, Hutchinson suggests that the human results should be interpreted with caution. The subjects were told that they would receive aversive stimulation, but the intensity would be tolerable. Also, he noted that subjects were paid to stay in the experiment, and most people would leave such a situation in everyday life.

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