Dorothy E. McAllister

CHAPTER 2 – Behavioral Measurement of Conditioned Fear1

Publisher Summary This chapter presents the current status of the concept of fear from a consistent viewpoint. Fear was considered to be a classically conditioned response, defined in terms of the prior appropriate pairing of neutral and noxious stimuli. As fear is unobservable, it may be measured only by its effect on other observable responses. Owing to this state of affairs, it is necessary, in studying fear, to maintain a clear conceptual separation between the fear response and the response used as its index. The chapter discusses four index responses that permit such a distinction. The chapter reviews the conditioning, measurement, and definition of fear. It focuses on aversive learning situations in which the conditioning of fear and its measurement are generally considered to be independent. Specifically, the interest will be in situations in which the noxious unconditioned stimulus is usually assumed to have its effect on the conditioning of fear but not directly on the measured response. The chapter describes four measures of fear and discusses some of the strengths and weaknesses of each measure and a theoretical rationale for the use of each as an index of fear.

Reward magnitude and shock variables (continuity and intensity) in shuttlebox-avoidance learning.

In Experiment I, eight groups of rats (n = 20) were given shuttlebox-avoidance training. Two levels of shock (.3 and 1.6 mA) were combined factorially with two levels of reward (large and small) under both continuous and discontinuous (.75 sec on and 2.00 sec off) shock. Visual situational cues were absent after a shuttle response for the large-reward condition and present for the small-reward condition. Superior performance was obtained with weak rather than strong shock under both reward conditions and with large rather than small reward only under the weak-shock condition. Continuity of shock had no differential effect on performance. Experiment II allowed the conclusion that the reward effect was attributable to a reinforcement mechanism. The data were taken as support for the effective reinforcement theory, which emphasizes the importance in avoidance learning of fear conditioned to situational cues.

Recovery of conditioned fear by a single postextinction shock: Effect of similarity of shock contexts and of time following extinction

Subjects in six experimental groups (n = 16 each) received one-trial passive avoidance (PA) training in which shock was delivered upon movement from a white wooden floor compartment to a black grid compartment. Then fear was extinguished (30 min) in the black compartment. After either 24 or 168 h, all the groups were treated in a room distinctively different from the training room. At each interval, one group received a shock in an apparatus similar to the conditioning box, another received a shock in a dissimilar apparatus, and another was placed in a neutral box. A PA test trial in the training apparatus indicated reinstatement of extinguished fear in all the groups given a postextinction shock except the 24-h dissimilar group. Control groups revealed that the extinction treatment was effective and that spontaneous recovery was not evident. The results were explained in terms of classical conditioning, stimulus generalization, and the broadening (flattening) of stimulus generalization gradients with time.

Escape-from-fear performance as affected by handling method and an additional CS-shock treatment

Experiment 1 demonstrated that hurdle-jumping, escape-from-fear (EFF) performance was affected deleteriously when the handling of the rats was by the tail rather than the body and was facilitated by the administration, just prior to EFF training, of one additional CS-shock pairing along with the opportunity to jump the hurdle. Additional experiments elucidated the basis for the effect of these two variables. Experiment 2 indicated that tail handling degraded performance by decreasing reinforcement. In Experiment 3, the facilitatory effect of the extra CS-shock treatment was found to result from the occurrence of a response at the termination of the pairing and not from the CS-shock pairing per se.

Reconditioning of extinguished fear after a one-year delay

After fear-conditioning (light-shock) trials in one side of a two-compartment apparatus, subjects learned in the absence of shock to jump a hurdle to the other (safe) side, thereby escaping the fear-eliciting stimuli. Speed of hurdle jumping increased to a maximum and then gradually decreased until a strict extinction criterion was reached. Then a single reconditioning trial led to the reemergence of hurdle jumping. Speed of responding was at a high level immediately and then gradually declined until the extinction criterion was met once again. One year later, without further fear conditioning, 2 of the subjects were given hurdle-jumping training until responding ceased. The subsequent administration of one fear-reconditioning trial led to an immediate recovery of rapid hurdle jumping followed by a gradual decrease in speed, just as had occurred a year before. These findings demonstrate that the reconditioning effects may be observed when a year has elapsed since original conditioning.

Investigations of the reinstatement of extinguished fear

Abstract In two experiments, fear was conditioned to the situational cues in one compartment of a hurdle-jumping apparatus and was then extinguished. Subsequently, either one shock (Experiment 1) or three or nine shocks (Experiment 2) were given in a situation distinctively different from that in which conditioning and extinction had taken place. Although some associative strength between the situational cues and fear was shown to have remained after extinction, in neither experiment did the postextinction-shock treatment increase the fear elicited by these cues: Escape-from-fear performance was no better in the shocked groups than in control groups given no additional shock. Thus, the nonassociative hypothesis which postulates that inflating the value of the representation of the UCS with shock-alone presentations can reinstate the extinguished fear of a stimulus was not supported. Rather, the results showed that, after extinction, an increase in fear of a simulus depended on further conditioning to that stimulus. The data also indicated that the nonvisual components of the situational cues predominated over the visual component.

Measurement of fear of the conditioned stimulus and of situational cues at several stages of two-way avoidance learning ☆

Abstract In Experiment 1, subjects were trained in a signaled two-way avoidance task to a criterion of either 2, 10, or 20 consecutive avoidance responses. Subsequently, they were allowed to escape, in the absence of shock, from one compartment of the avoidance apparatus to an adjacent safe box. For one group at each criterion level, the conditioned stimulus (CS) was presented during these trials; for another group, it was not (NCS). The rate and level of learning of the escape response were taken to reflect the amount of fear of the CS and situational cues present at the end of avoidance training for the CS groups and the amount of fear of the situational cues alone for the NCS groups. Under the CS condition, all groups learned equally well; under the NCS condition, learning occurred only in the two-criterion group. This pattern of results suggests that, as avoidance training continued, differential reinforcement led to the formation of a discrimination so that a substantial amount of fear was elicited by the CS plus situational cues but only a minimal amount by the situational cues alone. Such a loss of fear of situational cues would, according to effective reinforcement theory, serve to maintain or even increase reinforcement as avoidance training progressed. The results of Experiment 2, by ruling out some alternative explanations, supported the interpretation that the learning of the instrumental escape response in the first experiment was based on prior fear conditioning.

Fear determines the effectiveness of a feedback stimulus in aversively motivated insturmental learning

Abstract Three studies evaluated the role of feedback stimuli in an instrumental aversively motivated task. Rats were first given classical fear-conditioning trials (white noise-shock) in the start compartment of a two-compartment apparatus. They were then trained, in the absence of shock, to jump a hurdle from the start compartment to a “safe” compartment. For some groups, the fear-arousing situational cues and white noise CS were present in both compartments; for others, these fear-arousing cues were absent in the safe box. Also varied was the presence or absence of an external feedback stimulus (darkness or a flashing light) after the instrumental response. The results indicated that feedback stimuli can improve performance but only when sufficient fear is present following the response. In addition, the data revealed that darkness can be a more effective feedback stimulus than a flashing light but only when fear of visual situational cues is present. The facilitation of instrumental performance attributable to the presentation of a feedback stimulus was found to occur as early as the second trial. The findings generally support a reinforcement, fear-reduction/relaxation, interpretation of the role of feedback stimuli.

Pseudoavoidance responses in two-way avoidance learning

In a two-way avoidance learning task, responses sometimes occur during the CS-UCS interval prior to the initial receipt of shock. The number of such pseudoavoidance (PA) responses was found to be related positively to the number of avoidance responses made after the receipt of shock, implying that some of these avoidance responses were artifactual. The use of procedures that would decrease the occurrence of PA responses would also minimize this possible contamination of the avoidance data. Evidence was presented indicating that the frequency of PA responses was decreased when some amount of exploration of the apparatus, rather than none, was given prior to avoidance training, the shuttle compartments were separated by a small rather than a large guillotine door, a neutral rather than an intense auditory CS was used, and the CS-UCS interval was short (5 sec) rather than long (10 sec).