The sensory basis of avoidance responding in the rat : Relative dominance of auditory or visual warning signals and safety signals

Three experiments determined the relative degree of stimulus control exerted by the elements of a compound auditory-visual stimulus when this stimulus was presented in various temporal relationships to a barpress avoidance response. When the compound discriminative stimulus for barpress avoidance responding consisted of onset of white noise and onset of either light or darkness, the white noise always exerted dominant control. When the compound discriminative stimulus consisted of offset of white noise and onset of light, neither element controlled avoidance responding. On the other hand, when a barpress avoidance response produced a compound feedback stimulus consisting of onset of white noise and onset of either light or darkness, the visual element always exerted dominant control. When the compound feedback stimulus consisted of offset of white noise and onset of light, both elements exerted stimulus control.     

Constraints on Pavlovian aversive conditioning: Implications for avoidance learning in the rat

Four experiments investigated the relative degree of control exerted by several conditional stimuli when each stimulus: (a) preceded shock, (b) followed shock, and preceded a shock-free interval, (c) was independent of shock, or (d) was novel. When the onset of an auditory stimulus had preceded shock (Experiments 1, 2A, and 3), it always exerted conditioned excitatory control. When the same stimulus preceded a shock-free interval, it never exerted conditioned inhibitory control. When the onset of light (Experiments 2B, 4), silence (2C), or darkness (1, 2D) preceded a shock-free interval, it always exerted conditioned inhibitory control. However, when one of the latter stimuli preceded shock, it failed to exert excitatory control. Several models of this phenomenon were tested. The implications of these results for the species-specific defence reaction and two-factor theory accounts of avoidance learning were outlined.     

Fear inhibition and species specific defense reaction termination may contribute independently to avoidance learning

A series of three experiments was conducted to test the proposal of Cicala and Owen (Learning and Motivation, 1976, 7, 356–367) that warning signal termination reinforces avoidance learning by permitting fear to dissipate and that a feedback signal reinforces avoidance learning through conditioned inhibition of fear. A CER procedure with a second-by-second analysis was used to measure fear elicitation and fear reduction following classical conditioning or avoidance training. The results show that a feedback signal produces rapid and marked fear reduction, suggesting an inhibitory process. Although warning signal termination produced fear reduction, the slowness of this process suggests fear dissipation and not an inhibitory process. The combination of both events reduced fear no more effectively than a feedback signal alone. It is suggested that warning signal termination is effective in some avoidance learning situations not because it reduces fear, but possibly because it helps terminate an avoidance response that closely resembles a species specific defense reaction.     

Brief escape from a dangerous place: The role of reinforcement in the rat's one-way avoidance acquisition

Five experiments are reported which attempt to eliminate two possible sources of reinforcement in one-way avoidance learning: a period of escape from aversive apparatus cues and the termination of the warning signal (WS). A “brief escape”/one-way avoidance procedure was developed to minimize the time rats spent away from the shock box. It was found that, although prolonged escape from shock box cues contributes to the acquisition rate of one-way avoidance, it is not essential for relatively rapid acquisition to occur. It was also found, in agreement with earlier evidence, that WS termination makes no discernible contribution to learning in the one-way situation. Thus, neither source of reinforcement appears to be necessary for acquisition. At this point, one may argue either that reinforcement is not necessary for rapid one-way avoidance acquisition [e.g., Bolles' 1972 species-specific defense reaction hypothesis (In G. H. Bower (Ed.), The psychology of learning and motivation: Advances in research and theory (Vol. 6). New York: Academic Press, 1972)] or that there are other sources of reinforcement. As an example of the latter approach, a consummatory stimulus reward hypothesis is advanced.     

Pavlovian conditioned inhibition of fear during shuttlebox avoidance behavior

Three experiments explored the development and function of conditioned inhibition of fear during the acquisition and maintenance of shuttlebox avoidance behavior. The development of inhibition to an exteroceptive feedback stimulus was found to be a function of the number of successive avoidance responses to which the animal had been trained and of the duration of the intertrial interval, a parameter shown also to affect the rate of acquisition of avoidance learning. Master animals who learned the instrumental avoidance response, and yoked animals who did not, showed equivalent inhibitory fear conditioning in each experiment. The results of one experiment suggest that conditioned inhibition plays no important role in “protecting” fear conditioned to the discrete warning signal during avoidance maintenance. These data indicate that feedback stimuli develop their inhibitory properties by a Pavlovian process and that certain aspects of their function may, therefore, be readily understood within the framework of mediational two-process learning theory.     

Warning signal termination and a feedback signal may not serve the same function

Three experiments were conducted to test the possibility that a feedback signal (FS) and warning signal termination (WST), while equally reinforcing in the avoidance learning situation, reinforce through different underlying mechanisms. The first experiment showed that the reinforcing properties of an FS are reduced more than those of WST when these stimulus changes are made unreliable by the presence of shock following a CR on specified trials throughout acquisition. Experiment 2 confirmed this effect on avoidance performance when only a few punishment trials were administered following asymptotic avoidance acquisition. Experiment 3 demonstrated this effect during avoidance extinction with and without the presentation of punishment trials between acquisition and extinction performance. The results provided no support for the expectancy explanation of avoidance learning and were interpreted as consistent with the assumption that WST reinforces by permitting fear to dissipate and that the FS reinforces through fear inhibition.     

Shock signals and the development of stress-induced analgesia

We report five experiments in which we investigated the effects of "feedback signals" on the pattern of hypoalgesia produced by inescapable shocks. A 5-s lights-out stimulus coincident with shock termination had no effect on the naltrexone-insensitive (nonopioid) hypoalgesia, which occurred after 10 inescapable shocks, but completely blocked the naltrexone-sensitive (opioid) hypoalgesia, which followed 100 inescapable shocks. The stimulus prevented the development of the opioid hypoalgesia rather than merely masking its measurement. This effect did not depend on the use of lights-out as the stimulus but did depend on the temporal relation between the stimulus and shock. Stimuli immediately preceding or simultaneous with shock had no effect. Surprisingly, stimuli randomly related to shock also blocked the opioid hypoalgesia. Simultaneous measurement of both hypoalgesia and fear conditioned to contextual cues revealed that the level of fear did not predict the blockade of hypoalgesia. Different backward groups received different temporal gaps between shock termination and the signal. An interval between 2.5 s and 7.5 s eliminated the effect of the signal on fear, but 12.5-17.5 s were required to eliminate the effect of the signal on hypoalgesia. The opioid hypoalgesia blocking power of the random stimulus was entirely attributable to those stimuli occurring within 15 s of the termination of the preceding shock. The implications of these results for the explanation of stimulus feedback effects and for stress-induced analgesia are discussed.     

Avoidance conditioning as a function of appetitive stimulus pretraining: Response and stimulus transfer effects

Pretrained appetitive discriminative stimuli were used as warning signals in subsequent avoidance learning. In Expt 1 identical responses were required in pretraining and in avoidance learning. An appetitive S+ facilitated avoidance learning in rats in comparison to S? or a stimulus previously uncorrelated with food. In Expt 2, the type of response in pretraining and in avoidance learning was varied. Groups with homogeneous responses in the two situations replicated Expt 1 results, whereas groups with different responses in pretraining and avoidance learning failed to show an advantage when S+ served as warning; in the heterogeneous response groups, S? was as effective as S+. Inhibitory factors in the heterogeneous groups were discussed as an explanation for these results.     

Active role of the shock-avoidance contingency in shuttlebox-avoidance learning in Fischer344 rats

Different groups of Fischer344 rats acquired and maintained shuttlebox-avoidance responses under one, two, all three, or none of the shock-avoidance, warning-signal (WS) termination, and shock-escape contingencies. The intertrial interval was fixed at either 30 or 60 s. Removal of the shock-avoidance contingency led to a marked disruption of avoidance behavior at both intervals. This result was not produced by a selective punishment effect of the avoidance response by an inevitable shock. Thus, the shock-avoidance contigency provided particularly effective control over the avoidance learning. The WS termination contingency appeared to have little overall effect at the 60-s intertrial interval. It is suggested that response-contingent stimulus change served only as a discriminative cue for the absence of a shock.     

Effects of signaled versus unsignaled delay of reinforcement on choice

Pigeons chose between 5-s and 15-s delay-of-reinforcement alternatives. The first key peck to satisfy the choice schedule began a delay timer, and food was delivered at the end of the interval. Key pecks during the delay interval were measured, but had no scheduled effect. In Experiment 1, signal conditions and choice schedules were varied across conditions. During unsignaled conditions, no stimulus change signaled the beginning of a delay interval. During differential and nondifferential signal conditions, offset of the choice stimuli and onset of a delay stimulus signaled the beginning of a delay interval. During differential signal conditions, different stimuli were correlated with the 5-s and 15-s delays, whereas the same stimulus appeared during both delay durations during nondifferential signal conditions. Pigeons showed similar, extreme levels of preference for the 5-s delay alternative during unsignaled and differentially signaled conditions. Preference levels were reliably lower with nondifferential signals. Experiment 2 assessed preference with two pairs of unsignaled delays in which the ratio of delays was held constant but the absolute duration was increased fourfold. No effect of absolute duration was found. The results highlight the importance of delayed primary reinforcement effects and challenge models of choice that focus solely on conditioned reinforcement.     

Several types of learning increase open field activity in mice

Experimental and control groups of mice were initially matched on the basis of their open field activity. Experimental groups were trained in one of six types of learning tasks: (1) active avoidance conditioning with light and sound signals as conditioned stimuli and electric shocks as uncoditioned stimulus, (2) learning of a linear 5-point maze, (3) learning of a T-maze, (4) passive avoidance conditioning, (5) learning of non-aggressive behavior, and (6) learning of aggressive behavior. In all cases, learning was associated with a significant increase of the open field activity over that of the untrained but otherwise similarly treated control mice. This effect was most marked during the learning phase and disappeared when the acquired behavior had become firmly established. It is suggested that several types of learning are associated with an increase of arousal level, possibly mediated by the activation of central catecholamine neurons.     

STIMULUS EFFECTS ON LOCAL PREFERENCE: STIMULUS—RESPONSE CONTINGENCIES,STIMULUS—FOOD PAIRING,AND STIMULUS—FOOD CORRELATION

Four pigeons were trained in a procedure in which concurrent‐schedule food ratios changed unpredictably across seven unsignaled components after 10 food deliveries. Additional green‐key stimulus presentations also occurred on the two alternatives, sometimes in the same ratio as the component food ratio, and sometimes in the inverse ratio. In eight experimental conditions, we varied the contingencies surrounding these additional stimuli: In two conditions, stimulus onset and offset were noncontingent; in another two, stimulus onset was noncontingent, and offset was response contingent. In four conditions, both stimulus onset and offset were contingent, and in two of these conditions the stimulus was simultaneously paired with food delivery. Sensitivity to component food ratios was significantly higher when stimulus onset was response contingent compared to when it was noncontingent. Choice changes following food delivery were similar in all eight conditions. Choice changes following stimuli were smaller than those following food, and directionally were completely determined by the food‐ratio:stimulus‐ratio correlation, not by the stimulus contingency nor by whether the stimulus was paired with food or not. These results support the idea that conditional reinforcers may best be viewed as signals for next‐food location rather than as stimuli that have acquired hedonic value, at least when the signals are differential with respect to future conditions.     

Preconditioning of reinforcing properties to an exteroceptive feedback stimulus

Three groups of rats were given Pavlovian preconditioning by means of a yoking procedure and subsequently trained to avoid. One group received a light stimulus during preconditioning at the same times as the master avoiding animals received an exteroceptive feedback stimulus. During the subsequent avoidance training, this group was then given the same light stimulus as a feedback stimulus on successful avoidance trials. The group learned two-way avoidance in about the same number of trials as one-way avoidance is typically learned and substantially faster than two other control groups. These data indicate that feedback stimuli develop reinforcing properties by a Pavlovian mechanism. The data of the control groups indicate that feedback stimuli do not provide “information” about responding in the present situation.     

Cardiac deceleration in newborns: habituation, dishabituation, and offset responses.

Twenty healthy, 1–4 day-old infants were selected from a sample of 135 neonates on the basis of alertness during testing. The infants were presented mild intensity colored light with gradual onset and offset while heart rate was monitored. Half the infants received six exposures to blue light followed by two exposures to blue-green light, whereas remaining subjects received colors in reverse order. Stimulus duration was 20 sec and variable periods between stimuli averaged 30 sec. Results of trend analysis of variance of the second-by-second cardiac data indicated that for infants older than the median age, the decelerative responses to both stimulus onset and offset were significant. Further, these subjects' onset decelerations significantly habituated within the six stimulus repetitions and significantly dishabituated with change in the stimulus color. Offset decelerations incremented over habituation trials and decremented with change in stimulus color. Responses of younger subjects were more variable which probably reflects their less complete recovery from the effects of maternal medication and the birth process.     

Evidence against an occasion setting account of avoidance learning

Earlier studies on human avoidance learning showed that an avoidance response reduces the expectancy that a warning stimulus (WS) will be followed by an unconditioned stimulus (US). This modulation can transfer to WSs with which the avoidance response did not occur in the past. Recent studies suggest that transfer of modulation is selective in that it is stronger for WSs that previously went together with other avoidance responses than for WSs that never went together with an avoidance response. This finding has been interpreted as providing unique support for an occasion setting account of avoidance learning. We put forward alternative explanations of selective transfer of modulation in terms of the rate with which a WS was reinforced in the absence an avoidance response. In support of the alternative explanations, we found that transfer of modulation depended not on whether a WS previously went together with another avoidance response but on the rate with which the WS was reinforced in the past. We conclude that selective transfer of modulation in avoidance learning does not provide (unique) support for the occasion setting account. Our findings are in line with a revised expectancy model of avoidance learning.     

Contingency theory and the effect of the duration of signals for noncontingent reinforcement

Rats learned to approach a light that signaled food when food occurred only after the signal, but did not approach the light when food was equally probable regardless of the signal. When food unpaired with the light was preceded by a 5-sec noise, little learning was evident as well, but when the unpaired food was preceded by a 15-sec noise, approach to the light conditioned stimulus readily occurred. These effects of signal duration are similar to those previously obtained with the effect of free food on free-operant behavior and challenge existing theories of contingency effects in Pavlovian conditioning.     

A conditioned reinforcer maintained by temporal association with the termination of shock

Two experiments were conducted to determine whether a stimulus can be established as a positive conditioned reinforcer by associating it with the termination of shock, but without training the animal to make any response in its presence. In the first, six rats were conditioned to press a bar to terminate shock on a variable ratio schedule; white noise was then substituted as the immediate consequence, with the shock terminating 30 sec after the last press in its presence. It was found that the rate of pressing in the absence of noise depended on the contingency between the pressing and the noise. The second experiment sought to determine whether the difference in rates before and after the onset of the noise was due to the reinforcement of prior responding by the onset of the noise or to the suppression of subsequent responding by differential reinforcement of competing behavior. Six more rats were trained in the same manner, but with shock terminating 30 sec after the onset of the noise, regardless of what the animal did in its presence. Again the rate was higher before the onset of the noise, indicating that pressing was indeed maintained by the noise as a conditioned reinforcer.     

Occasion setting of timing behavior

Rats were trained on a temporal switching discrimination, with 2 features, A and B, signaling 2 target conditioned stimuli, x and y; feature offset and target onset were separated by a 5-s feature-target interval, and all target stimulus presentations terminated in a food pellet. The target conditioned stimuli were either short or long (6 or 30 s): Specifically, when signaled by A, x was 6 s and y 30 s, but when x and y were signaled by B, x was 30 s and y 6 s. Trials with 6-s and 30-s targets were termed short and long trials, respectively. Probe tests indicated that the animals correctly anticipated when food was to be delivered on these 2 types of trials. In further testing, the interval between feature offset and target onset was lengthened, to investigate the precise mechanism underlying this behavior. This manipulation did not have a substantial effect on discrimination performance. These results are discussed with reference to theories of occasion setting, timing, and configural learning.     

Children's avoidance responses to three probabilities of threatened consequences

Children's avoidance responses were conditioned and then extinguished in a laboratory analog of a social threat situation. Aversive events (story interruptions) were programmed to follow either 100% (group E100) of the signals (threats), 60% (group E60) of the signals, or 20% (group E20) of the signals during acquisition. The subjects could avoid the signal and/or the aversive event by responding with lever presses above criterion level. Results indicated that groups E100 and E60 were generally not different from each other but avoided significantly more interruption and signals and responded at a higher rate than group E20. Groups E100 and E60 both shifted their responding from approximately equivalent probabilities of signal and interruption avoidance to relatively greater avoidance of interruptions during acquisition, and then shifted back to equivalent probabilities of signal and interruption avoidance during extinction. Results were discussed in terms of the function of threats as discriminative stimuli.     

Conditioned behavioral and physiological changes associated with injections of a narcotic antagonist in morphine-dependent monkeys

Environmental stimuli which are repeatedly associated with the nalorphine-induced withdrawal syndrome in morphine-dependent monkeys acquire the ability to produce a variety of conditioned behavioral and physiological responses. Morphine-dependent rhesus monkeys were studied under a fixed-ratio schedule where every tenth lever press produced a food pellet. After several pairings of a stimulus (light or tone) with intravenous injection of a dose of nalorphine which produced an immediate and severe withdrawal syndrome, onset of the stimulus alone produced conditioned suppression of lever pressing, heartrate decrease, vomiting and salivation. Conditioned suppression of responding and conditioned heart-rate changes persisted in post-dependent monkeys for one to four months after termination of chronic morphine treatment. No conditioned electrocardiogram, respiration or temperature changes were ever seen. A second group of morphine-dependent rhesus monkeys was studied under a schedule where every lever press produced an intravenous injection of morphine. After 10 pairings of a light with the intravenous injection of a dose of nalorphine which produced marked withdrawal signs and increased responding for morphine, presentation of the light and injection of sahne produced conditioned increases in responding for morphine. A third group of morphine-dependent rhesus monkeys was studied under a schedule where every nth lever press (n = 1 to 10) terminated a stimulus light associated with periodic injections of nalorphine or naloxone; lever-press responding was engendered and subsequently maintained. Thus, stimuli associated with the nalorphineor naloxone-induced withdrawal syndrome can either suppress, enhance or maintain behavior depending on the schedule conditions.