Backchaining of relaxation in the extinction of avoidance

After rats were trained in one-way avoidance, two types of nonshock treatment were given to assess the degree to which fear of the shock area is affected by (a) nonshock responding (regular extinction trials) apart from (b) repeated exposure to the shock area in the absence of shock (response prevention). Different groups of regular extinction rats received 1 or 27 trials; response prevention control rats were equated with regular extinction rats on amount of nonshock exposure to the shock area and other variables. Fear of the shock area was measured on a posttreatment passive avoidance test. Regular extinction trials led to less fear of the shock side than response prevention trials when 27 nonshock trials were given. The results (a) suggest that relaxation back-chains from the safe to the shock area over repeated avoidance extinction trials, and (b) clarify existing problems of maintained fear with the response prevention technique.     

The significance of crossed and uncrossed projections for the acquisition and retrieval of visual engrams in hooded and albino rats

Summary Occlusion of one eye and functional hemidecortication by cortical spreading depression (CSD) were used to examine the relative importance of crossed and uncrossed visual projections for pattern discrimination learning in hooded and albino rats. Whereas functionally hemidecorticate albino rats were unable to learn in 200 trials a horizontal-vertical discrimination when using the eye contralateral to the depressed hemisphere, hooded rats needed under similar conditions three times as many trials to criterion (167) than when using opposite eye and hemisphere (59). An engram established in intact animals with both eyes could be retrieved in functionally hemidecorticate rats of both strains even with the eye ipsilateral to the intact hemicortex, but retraining required about twice as many trials as when using the contralateral eye. Retrieval of monocularly acquired engrams was less efficient under similar conditions. Pattern discrimination formed through crossed or uncrossed visual projections during monocular occlusion and contralateral or ipsilateral CSD was completely lateralized, since relearning with naive eye and hemisphere proceeded at the same rate as the original learning. On the contrary, a black-white discrimination trained with the eye contralateral to the depressed hemisphere could be partly retrieved by the untrained eye and hemisphere. It is concluded that the ipsilateral visual projection is more effective in hooded than in albino rats and that it can be more efficiently used for retrieval than for acquisition.This research was partly supported by the Foundations' Fund for Research in Psychiatry, Grant G69-453.     

Dissociative effects of different types and amounts of nonreinforced CS exposure on avoidance extinction and the CER

Two experiments examined the effectiveness of two amounts of flooding or response-prevention on hastening avoidance response extinction and on reducing CS-produced suppression of bar-pressing for food. In Experiment 1, 20 and 30 flooding trials were both shown to be effective in hastening the extinction of a well-learned shuttlebox avoidance response. In Experiment 2, rats trained under comparable conditions to those in Experiment 1 were tested following flooding for the CER in a different apparatus. The results indicated that 30, but not 20, flooding trials were sufficient to reduce the CER. In each experiment the results of additional control groups equated with the flooded groups for nonreinforced CS exposure also revealed a dissociation between the effectiveness of this CS time control procedure in hastening avoidance response extinction and in reducing the CER. Further comparisons showed that although 30 flooding trials did reduce the CER, the same total duration of nonreinforced CS Exposure in the form of avoidance extinction trials did not. Thus the context in which CS exposure occurs may affect the dynamics of extinction of the CER. The experiments are discussed in the broader context of dissociation of various indices of fear in humans.     

Effects of temporal placement of response prevention on extinction of avoidance in rats

Two experiments investigated the effects of prior extinction trials upon the effectiveness of response prevention procedures (flooding) in facilitating extinction of avoidance in rats. The results showed that both prior CS only extinction trials and response prevention independently hastened extinction and that response prevention is enhanced if prior extinction has already taken place. The results were interpreted as being consistent with a relaxation interpretation of extinction of avoidance behavior providing a ‘distraction’ or ‘attention shift’ factor is incorporated into theory.     

The effects of single-component extinction of a three-component serial CS on resistance to extinction of the conditioned avoidance response

Central to a fear interpretation of how avoidance responses are maintained in the absence of further CS-UCS pairings is the underlying assumption of an existing gradient of fear across the CS-UCS interval. Extrapolations based on this gradient lead to a number of differential predictions concerning the topography of avoidance responding during extinction. The present research was concerned with the differential effects of extinguishing separate components of the CS complex upon responding to the complete CS complex during extinction. In Phase 1 of the study, rats were classically conditioned to a three-component serial CS (S₁/S₂/S₃) followed by shock. Each subject was then given avoidance training in a one-way apparatus to a criterion of one successful avoidance. In Phase 2, subjects were divided into four groups, with three of the groups receiving nonreinforced exposure for 25 trials to one of the components of the serial CS (S₁, S₂, or S₃). The fourth group (S₀) was exposed for the same period of time to the apparatus cues. In Phase 3, the total stimulus complex was reintroduced in its original order, and animals were tested until extinction of the instrumental response was reached. The results are consistent with the hypothesis that a fear gradient exists in extinction and decreases in magnitude as the distance from the point of UCS onset increases.     

The restoration of extinguished avoidance responses

Following extensive signaled shuttlebox avoidance training, Fischer 344 rats were given extinction trials until they reliably stopped responding and, thereafter, they received occasional classical CS-UCS pairings during the course of restoration test trials in which shock was absent. Experiment I demonstrated that the classical contingency was both necessary and sufficient for the complete recovery of such behavior. Experiment II revealed that the degree of recovery was not differentially affected by the frequency of such CS-UCS pairings. However, in Experiment III recovery in the presence of this contingency was shown to depend on the number of previous extinction trials, although even after a large number of such trials, a considerable degree of recovery occurred. These findings demonstrated the central role of the classical CS-UCS contingency in restoring a previously extinguished avoidance response.     

Acquisition and extinction of signaled avoidance as a function of intermittent reinforcement

Signaled, shuttle-box avoidance responding in female rats of the Fischer₃₄₄ strain was examined as a function of four separate contingencies of intermittent reinforcement. In Experiment 1, when avoidance responses during acquisition were reinforced 25% of the time with prompt CS termination, animals responded equally often during acquisition and significantly more often during extinction than animals who received such reinforcement on a 100% schedule. Similar results were found under a trace procedure in Experiment 2 when avoidance responses were reinforced 25% of the time with informational feedback stimuli. In contrast, during Experiment 3, when animals were shocked on only 25% of the trials on which they failed to respond, the level of avoidance responding during both acquisition and extinction was significantly less than it was when animals were shocked on a 100% schedule. Comparable results were found in Experiment 4 when avoidance responses during acquisition averted shock on only 25% of the trials. Thus, intermittent reinforcement contingencies involving response-contingent feedback stimuli and shock have differential effects on avoidance responding during both acquisition and extinction trials under the signaled avoidance procedure.     

The effect of UCS intensity in classical and avoidance GSR conditioning

This study compared GSR avoidance and yoked-control conditioning procedures. Classical conditioning at two UCS intensities was followed by extinction and, two months later, by an avoidance session. Matching of Ss was based on GSR responsiveness and classical conditioning in the first session. The strong UCS led to more rapid reduction in CR latency (due to an increase in number of Ss responding) in the first session, and there was a tendency for maximum CR magnitude to occur in fewer trials with the strong UCS. No UCS-intensity difference in level of responding to the CS or UCS was found in the first session. A greater amount of spontaneous recovery in the second session was found in the strong UCS group. The avoidance and yoked control groups did not differ in CR magnitudes, latencies, or frequencies, nor in UCR magnitudes in the second session. They did differ significantly in the rate of decline in intertriai responses, the decline being more rapid in the avoidance condition.     

Pavlovian processes and response competition as determinants of avoidance response-prevention effects

Two experiments investigated the facilitation of avoidance extinction by exposure to lengthy (5-sec) shock during avoidance response prevention. In Experiment 1, animals exposed to light only or to light-shock pairings during response prevention showed equal facilitation of extinction relative to shock-only animals or to animals receiving no response prevention. Preshock rearing, directly antagonistic to the avoidance response, developed for shocked animals during response prevention and persisted during extinction for light-shock animals. Immediately before extinction, half of each group was permitted a single escape from a light-shock compound by means of the response previously required for avoidance. The only effect was upon the extinction performance of light-shock animals. Rearing was eliminated and extinction responding increased to a level far above that for any of the other animals. Experiment 2 demonstrated that the shock-only treatment affected the extinction performance and rearing of nonescape and escape animals in a manner entirely equivalent to the effects of the light-shock treatment of Experiment 1, provided stimulus conditions (light absent) were the same for all experimental phases. Thus, lengthy shock during avoidance response prevention simultaneously leads to the acquisition of competing behavior and enhances control by a warning signal or contextual stimuli over the avoidance response. Implications for the CS-only response-prevention treatment and the transfer of aversive control are discussed.     

Is aversive learning a marker of risk for anxiety disorders in children?

Aversive conditioning and extinction were evaluated in children with anxiety disorders (n=23), at-risk for anxiety disorders (n=15), and controls (n=11). Participants underwent 16 trials of discriminative conditioning of two geometric figures, with (CS+) or without (CS-) an aversive tone (US), followed by 8 extinction trials (4 CS+, 4 CS-), and 8 extinction re-test trials averaging 2 weeks later. Skin conductance responses and verbal ratings of valence and arousal to the CS+/CS- stimuli were measured. Anxiety disordered children showed larger anticipatory and unconditional skin conductance responses across conditioning, and larger orienting and anticipatory skin conductance responses across extinction and extinction re-test, all to the CS+ and CS-, relative to controls. At-risk children showed larger unconditional responses during conditioning, larger orienting responses during the first block of extinction, and larger anticipatory responses during extinction re-test, all to the CS+ and CS-, relative to controls. Also, anxiety disordered children rated the CS+ as more unpleasant than the other groups. Elevated skin conductance responses to signals of threat (CS+) and signals of safety (CS-; CS+ during extinction) are discussed as features of manifestation of and risk for anxiety in children, compared to the specificity of valence judgments to the manifestation of anxiety.     

Avoidance of heat by rats: Effects of thermal context on rapidity of extinction

Rats were trained to avoid radiant heat in a one-way, jump-up apparatus. The animals that could avoid heat responded more frequently and more rapidly than did yoked controls that received heat, but for whom no avoidance contingency was deliberately arranged. Control animals trained with light, rather than heat, did not learn to avoid. Using this jump-up avoidance, rats were trained to avoid heat in a room maintained at 27°C. They were then given a series of extinction trials, with no heat presentations, with the temperature maintained at either 27 or 7°C. Placing the rats in a cold environment facilitated extinction of heat avoidance behavior, but only in animals that had previously experienced heat while they were in the cold. Prior heat experience administered in a warm, rather than cold, context was not sufficient to potentiate the effect of ambient temperature on avoidance extinction. Implications of these results for theories of avoidance learning are discussed.     

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.     

Determinants of instrumental extinction in terrestrial toads (Bufo arenarum)

Previous research in a water-reinforced instrumental training situation with toads (Bufo arenarum) has shown that performance in both acquisition and extinction is poorer after partial, rather than continuous reinforcement training. In Experiment 1, the performance of a group receiving 24 trials on a 50% partial reinforcement schedule was poorer in acquisition and extinction than that of continuously reinforced groups matched for trials or reinforcements. However, partially reinforced toads extinguished at the same rapid rate as a continuously reinforced group that received training only on the days in which the partial toads received water reinforcement. In Experiment 2, extinction was faster after 10 reinforced acquisition trials than after 30 trials. This evidence suggests that the deleterious effects of partial reinforcement in toads can be explained by a combination of two factors, namely, the distribution of reinforced trials across days and the total number of reinforcements.     

Overlearning and instructional control of extinction of vasomotor responding

In a previous study by the authors, immediate extinction of conditioned vasomotor responding was obtained, under conditions of both continuous and partial reinforcement, when the UCS delivery apparatus was removed and subjects were informed that there would be no further UCS presentations. The present study varied the number of continuous reinforcement trials using the same conditioning procedure. Forty human subjects were randomly divided into two groups, given thermal vasomotor conditioning procedures on either 25 or 100 continuous reinforcement trials. At the onset of extinction half of each group was given traditional noninformed extinction procedures, while the other (informed) half had the thermal stimulator removed. Immediate extinction was obtained in informed subjects given 25 conditioning trials. However, there was no significant reduction of responding in informed subjects given 100 conditioning trials. Consequences for behavior theories and therapies are discussed.     

Psychophysiological responses during analogue systematic desensitization and non-relaxation control procedures

This investigation tested the hypotheses than an analogue systematic desensitization procedure (SD) would be both more effective and more efficient than a comparable non-relaxation control procedure (NRC) with respect to subjective report, behavioral and psychophysiological variables. Phobic subjects responded to slides depicting a feared aversive stimulus. The SD procedure resulted in significantly less reported fear, fewer trials to a criterion level of decrease in subjective fear, and significantly greater decreases in ANS baseline measures. However, measures of behavioral avoidance and measures of decrease in psychophysiological responsivity to the aversive stimuli revealed significant changes within both SD and NRC groups, and no significant differences between the groups, whether or not the groups were equated for number of stimulus presentations. The results, indicating equivalent efficacy and efficiency for the SD and NRC procedures, suggested a limited role for relaxation in systematic desensitization. An extinction or habituation hypothesis was supported at the expense of a counterconditioning hypothesis.     

Determinants of fear over the course of avoidance learning

Most theorists have explained attenuation of fear over the course of avoidance learning by assuming that fear extinguishes with repeated nonreinforced avoidance trials. Experiment 1 replicates the finding that rats trained to a criterion of 27 consecutive avoidance responses (CARs) show less fear during the CS than rats trained to a criterion of 3 or 9 CARs. This attenuation of fear cannot, however, be accounted for by simple Pavlovian fear extinction, because yoked partners receiving the exact same pattern of CSs and USs did not show this attenuation and did not differ from yoked partners receiving only reinforced CS presentations. Experiment 2 found that feedback from the master avoidance learner's response is sufficient to produce this attenuation in yoked animals; “control” per se is not necessary. Several possible explanations are discussed regarding the mechanism underlying this role of feedback in diminishing fear of the CS in the avoidance learning context.     

Prior exposure to inescapable electric shock in rats affects extinction behavior after the successful acquisition of an escape response

In Expt 1, rats exposed to 64 inescapable electric shocks in a restrainer or merely restrained were later given either 0, 5, 15 or 30 escape/avoidance training trials with a two-way shuttlebox procedure that does not lead to interference with escape acquisition due to prior exposure to inescapable shock. After escape training all rats were given an escape/avoidance extinction procedure in which shock was inescapable. The rats which had received prior exposure to inescapable shock responded less often and with longer latencies in extinction than did the restrained rats. Experiment 2 demonstrated that this effect is caused by the inescapability of the initial shock treatment. These results were explained in terms of (a) associative interference which minimized the effect of shuttlebox escape training for the preshocked subjects, and (b) a stronger tendency to recognize the presence of an inescapable shock situation during extinction for the preshocked subjects. The relationship between these results and previous work demonstrating that exposure to the escape contingency mitigates the effects of inescapable shock exposure was also discussed.     

Extinction of responding maintained by timeout from avoidance

The resistance to extinction of lever pressing maintained by timeout from avoidance was examined. Rats were trained under a concurrent schedule in which responses on one lever postponed shock on a free-operant avoidance (Sidman) schedule (response-shock interval = 30 s) and responses on another lever produced 2 min of signaled timeout from avoidance on a variable-ratio 15 schedule. Following extended training (106 to 363 2-hr sessions), two experiments were conducted. In Experiment 1 two different methods of extinction were compared. In one session, all shocks were omitted, and there was some weakening of avoidance but little change in timeout responding. In another session, responding on the timeout lever was ineffective, and under these conditions timeout responding showed rapid extinction. The within-session patterns produced by extinction manipulations were different than the effects of drugs such as morphine, which also reduces timeout responding. In Experiment 2 shock was omitted for many consecutive sessions. Response rates on the avoidance lever declined relatively rapidly, with noticeable reductions within 5 to 10 sessions. Extinction of the timeout lever response was much slower than extinction of avoidance in all 4 rats, and 2 rats continued responding at baseline levels for more than 20 extinction sessions. These results show that lever pressing maintained by negative reinforcement can be highly resistant to extinction. The persistence of responding on the timeout lever after avoidance extinction is not readily explained by current theories.     

Effect of classical conditioning on an internal clock

Six experiments with rats used a psychophysical choice procedure to study the internal clock used to discriminate duration. They investigated if the clock is sensitive to the signal value (associative strength) of a stimulus. The experiments involved two types of trials. On choice trials, a stimulus lasted a short (e.g., 3 s) or long (e.g., 12 s) duration; then the rats chose between two levers. The rewarded choice depended on the duration of the stimulus. On conditioning trials, the stimulus used on choice trials was presented, but it ended without food (extinction trials) or with food (pairing trials) regardless of what the rat did. The main stimulus minus accuracy with the long stimulus. Experiment 1 showed that extinction trials increased short bias relative to training without conditioning trials or to training with pairing trials. The rest of the experiments tested explanations of these results. The same results were found when extinction trials were the same duration as the short stimulus (Experiment 2), when extinction trials were a random duration (Experiment 5), and when the signal value of the conditioned stimulus was changed in another way (Experiment 6). The effect of conditioning trials was modality specific (Experiments 3 and 4). Of the explanations considered, the best one--the only one not contradicted at least once--is that changing the signal value of a stimulus changes how the clock times the stimulus. Reducing signal value reduces the measured duration.     

Flooding as a function of shock level and length of confinement

In a one-way avoidance learning situation with rats, response prevention trials facilitated extinction as an increasing function of the duration of the prevention interval for shock levels below 1.8 mA. For 1.8 mA, extinction was a nonmonotonic function of the response prevention interval, with 15- and 210-sec durations showing the most facilitation of extinction. For all response prevention intervals except 15 sec, trials to extinction was a direct function of shock level. For 15 sec, it was an inverse function of shock level. The unexpected interaction of shock level with prevention interval was explained by invoking the concept of relief.