- Email: [email protected]
Counterconditioning and exposure-only in the treatment of specific (conditioned suppression) and generalized fear in rats
Behav. Res. & Therapy, 1973, Vol. 11, pp. 453 to 461. Pergamon Press. Printed in England
COUNTERCONDITIONING AND EXPOSURE-ONLY IN THE TREATMENT OF SPECIFIC (CONDITIONED SUPPRESSION) AND GENERALIZED FEAR IN RATS* DENNIS J. DELPRATO and DONALD E. JACKSON Department of Psychology, Eastern Michigan University, Ypsilanti, Michigan 48197, U.S.A.
Summary-In Experiment 1 the conditioned suppression technique was used to condition specific fear, suppression of operant lever pressing for food to a discrete CS. The eficacy of four treatment conditions on fear reduction was evaluated. Countercondjtjoning in which exposure to the CS was ~ntiguously paired with food was significantly less effective than noncontiguous CS exposure and food. An exposure-only effect was indicated by the superiority of all three treatments involving CS exposure (the above two plus a typical conditioned suppression extinction procedure) to treatment consisting of food only. The reverse counterconditioning effect and the exposure effect are consistent with current views that emphasize the centrality of aversive stimulus exposure in fear reduction. Experiment 2 investigated elimination of generalized fear produced by unsignalled, inescapable shocks in the lever-pressing apparatus. Two treatments (counterconditioning and exposure-only) were equally effective and they were superior to no exposure csntrol treatment. The results of the two experiments reinforce recent attempts toward a reevaIuation of the role of anxiety-competing responses in elimination of fear.
COUNTERCONDITIONING, the operation of pairing stimuli that elicit anxiety/avoidance competing responses with conditioned aversive stimuli, has been used successfully by behaviorally oriented therapists in the treatment of maladaptive avoidance and fear (anxiety) behavior (e.g. Wolpe, 1969). However, the critical variables underlying the efficacy of counterconditioning have not been isolated in controlled research. Since exposure to the conditioned aversive stimuIus in the absence of primary aversive stimulation (exposure-only) is an inherent feature of counterconditioning, and given that such treatment has been shown to reduce fear and avoidance (cf. Baum, 1970), effects of coL~nterconditioning must be evaluated in comparison with exposure-only treatment conditions in which exposure and anxiety/avoidance competing responses are noncontiguous. Diminutions in fear and avoidance can be attributed to counterconditioning to the extent that counterconditioning is superior to exposure-only. Consideration of human and infrahuman experiments reveals that counterconditioning may be more effective than exposure-only in certain circumstances, although most findings are equivocal. For example, while Davison (1968) found graded exposure to aversive stimuli contiguous with anxiety-competing relaxation more effective in reducing snake avoidance in female undergraduates than graded exposure alone, Nawas, Mealiea and Fishman (1971) obtained equivalent behavior changes with contiguous and noncontiguous relaxation and exposure. At the infrahuman level, Wilson and Dinsmoor (1970) reported that exposure combined with feeding on a platform led to greater reductions in passive avoidance (fear) of a grid floor below the platform than platform exposure-only; however,
* Supported in part by Grant MH20833-01 from the National Institute of Mental Health. 453
454
DENNIS
J. DELPRATO
and EKfNAtD E.
JACKSON
counterconditioning was not more effective than ~on~ned exposure to the grid without food. Poppen (1970) used the conditioned emotional response or conditioned s~~ppression technique (Estes and Skinner, 1941) with rats and found results analogous to those of Davison (1968), i.e. graded exposure to the tonal CS contiguous with response independent (‘free’) food was superior to graded exposure-only in reducing suppression (fear) to the CS. F-fowever, Nawas et a/.‘~ (1971) criticism of Davison’s finding can be applied to Poppen’s situation in that the latter failed to include a condition with noncontiguous exposure and free food. Gordon and Baum (1971) first trained rats to perform an active avoidance response by jumping up to a ledge in an avoidance apparatus. C~unter~ollditioning treatment consisting of forced exposure to the apparatus paired with positive intra~ra~~ial stimulation (ICS) produced greater reductions in avoidance than either apparatus exposure alone, ICS in a neutral area, or exposure to a neutral area. Unf~rtui~ately Gordon and Baum’s failure to include a treatment comprised of nol~~ontiguous apparatus exposure and ICS precludes an L~nequivocaI interpretation of their results in terms of counterconditioning. Since the question of the relative efficacy of coL~nter~onditio~lillg and exposure-only in the reduction of fear has practical and theoretical impIications, the present research compared these two methods under conditiQns designed to obviate interpretative problems such as the above. In Experiment 1, the conditioned suppression paradigm was used to condition fear to a discrete stimulus (CS). The empirical measure of fear in this paradigm is the suppression of ongoing appctitive operant behavior produced by a CS that has been paired with shock. Counterconditioning consisted of response-independel~t presentations of food during the CS. Two basic control conditions included (a) ~~t~~olltiguo~ls food and CS exposure and (b) food only (no exposure). Greater reductions in suppression with count~r~ond~t~onil~g than with noncontiguous food and exposure would seem to of&r unanlbigLlous evidence that pairing an anxiety-con~peti~~~ response with exposure (~our~terconditioning} adds to whatever effects exposure per se has. Comparison of the two exposure treatments with no exposure treatment should reveal whether treatment was prolonged enough to produce an exposure effect. This latter comparison is important since failure to obtain a counterconditioning effect could be the result of an insufficient number of treatment trials, in which case even an exposure effect may not be obtained. On the other hand, if treatment is sufficient to produce an exposure effect, it seems more likely that treatment has been prolonged enough to allow a ~oLlnter~onditioniilg effect to operate.
The 5’s were 20 nai’ve male albino rats {,Sprague-Daw~e}~) obtained from Spartan Research Animals, Haslett, Michigan. They were individually caged under constant illumination with free access to water. At the beginning of experimentation, weights ranged from 300 to 356 g, with a mean of 332 g. Restricted feedings of Purina Rat Chow reduced weights to 80 per cent of predeprivation weight, a level maintained throughout the experiment. Ali testing was done in IO identical 30.5 x 24 x 27 cm Lehigh Valley Electronics duafbar rat chambers (right lever permanently retracted). The Aoor of each chamber was constructed of 0.48 cm dia. stainless steel rods, 1.90 cm apart center to center. Each chamber was enclosed in a blower-ventilated, s~~ind-attenuating chest located in a separate cubicle. Each unit was equipped with a speaker mounted on the wali of the chest 30 cm from the lever, print-out counter, Model 113-04 Lehigh Valley shocker-scrambler, and solid state
TREATMENT
OF SPECIFKC AND GENERALfZED
FEAR fN RATS
455
control modules. Reinforcement (45..mg Noyes pellets) availability and CS presentations were controlled from a central source in an adjacent room. The CS was a 2-min white noise produced by two Grason-Stadler noise generators (Model 901s). Each generator served five chambers. Noise level readings (X0 dB & 1 re 0.0002 dynes/cm2) were taken at the response lever. The US was a 0.5 set, 1.5 mA shock.
Procedure Pr~~i~~?i~~ar~~ tmkiq. On the first day, Ss self-trained to a criterion of 50 reinfor~ments CRF. Shaping was used where necessary. The following day, Vi I-min training began and consisted of five I-hr sessions over 3 days. Fear ~~~~i~s~tioi~.The next day, two five-trial fear conditioning sessions were held while Ss responded on the VI schedule. In the morning, five 2-min CSs were given with the shock US delivered as each CS terminated. CS onsets occurred at 6, 16, 24, 33 and 41 min into the 45 min session. In the afternoon, CS onsets occurred at 7, 16,23,33.5 and 42 min into the 45 min session. The next morning, two additional fear conditioning trials were given with CS onsets at 10 and 30 min into the 35min session. Shock was not used for the remainder of the experiment. Dijkrcntial treatment. On the day following the last fear conditioning trial, Ss were randomly assigned to one of four groups (12 = 5 per group) for differential treatment, Group Normal Extinction (NExt) Ss had the response Iever available with food responsecontingent on the original VI schedule, This group, the onfy group with access to the Iever in treatment, was included to permit monitoring of suppression throughout treatment and as a typical conditioned suppression extinction conditiol~ with which the other treatments could be compared. Group Co~lnterconditioning {CC) Ss had the lever retracted and received 15 “free” pehets during each of six 2-min CS presentations. The 1.5 pellets were unsystematically spaced during each CS. Group Nonconti~uoLls Food and CS exposure (NF-CS) Ss had the lever retracted and received 15 free pellets during each of six post-CS (nor&S) periods. The 2-min non-CS intervals for Group NF-CS began from 1 to 3 min after termination of the previous CS and terminated 2-4 min prior to the next CS onset. Group No Exposure, Food-Only (FO) Ss received treatment identical with that of Group CC except the CS was never presented; food was presented to FO Ss at the same time it was presented to Group CC Ss, Thus all groups except NExt received 90 free pellets and all groups except FU received six 2-min CS exposures in treatment. The CS exposure groups had CS onsets at 6, 15, 25, 33,43 and 51 min into the 57-min session. Onsets of the six 2-min nor&S periods (Group NF-CS) were 10, 20, 29, 37, 46 and 54 min into the session. Post-tr~~t~e~t test. On the day following treatment ah Ss received six 2-min CS presentations at 6, 12, 21, 29, 36 and 46 min into the 50-min session, The lever was avaifable with food response-contingent on the original VI I-min schedule. Index of suppression. CS effects on bar pressing were assessed by the commonly used suppression ratio, B/(A + El), where B represents the number of responses emitted during the 2-min CS and A refers to the number of responses emitted during the 2-min period immediately prior to CS onset. A ratio of 0.50 indicates no CS effect while a ratio of O,oO indicates complete CS-produced suppression. Ratios for each S were computed for each trial during fear acquisition and the post-treatment test and for NExt Ss during treatment.
456
DENNIS J. DELPRATO
RESULTS
and DONALD
E. JACKSON
AND DISCUSSION
Fear acquisition and d@erential treatment Conditioned suppression to the discrete CS was rapidly acquired in a comparable manner in the four groups. Mean suppression ratios in the various groups ranged from 0.00 to 0.07 on Trial 6 and from 0.00 to 0.02 on the last trial. An analysis of variance of the acquisition scores indicated the groups were statistically equivalent prior to differential treatment (F= 1.13). Mean suppression ratios of Group NExt over the six extinction trials in treatment were 0.01, 0.02, 0.07, 0.14, 0.27 and 0.27, respectively. All Ss in Group NExt showed an increase in their ratios from the first to the last trial, indicating extinction of suppression. The eating behavior of Ss in the three groups that received free pellets in treatment was observed and latency to begin eating upon receipt of the first pellet of each series of 15 pellets was measured with a stopwatch. The median latencies to eat on the first series were 2, 2 and 4 for Groups CC, NF-CS, and FO, respectively. While one S in Group CC did not eat in the presence of the CS on the first series, it promptly began eating upon termination of the CS. On only one other occasion did a CC rat not eat in the presence of the CS. Aside from these two episodes, there appears to be no other way in which the group with the CS present during food presentation (Group CC) differed either quantitatively or qualitatively from the groups with CS absent during food presentation (Groups NF-CS and FO) in responsiveness to the food.
FO I I
I 2
I 3
I 4
I 5
I 6
Trio1
FIG. 1. Mean suppression ratios of the four treatment groups in post-treatment. CC r= Counterconditioning, NF-CS = Noncontiguous Food and CS exposure, FO = Food Only, NExt = Normal Extinction.
Post-treatment test. Mean suppression ratios over the six trials in post-treatment are shown in Fig. 1. The results are not consistent with the suggestion that contiguous pairing of aversive stimulus exposure and food is more effective in reducing fear than noncontiguous presentation of food and exposure since Group CC was more suppressed throughout the test than was Group NF-CS. The basic analysis of the data involved partitioning the treatment variable into two independent components which enabled comparison of the three CS exposure grouIjs (NExt, CC and NF-CS) with the nonexposure condition (FO) and of
TREATMENT
OF SPECIFIC
AND GENERALIZED
FEAR IN RATS
457
NExt vs. CC vs. NF-CS. The analysis yielded a significant effect for the nonexposure vs. combined exposure comparison over all test trials (t; = 10.26, p < 0.01). The F-value for between-group variation among the three exposure groups fell short of significance at the 0.05 level (F = 3.02, p < 0.10); however, individual comparisons via Duncan’s Multiple Range Test indicated that Group CC was significantly more suppressed than Group NFCS. Group NExt differed from neither Group NF-CS nor Group CC (p > 0.05). The main finding of this experiment was that exposure to the aversive stimulus, whether paired or unpaired with food and eating, was sufficient to reduce the acquired fear-eliciting capacity of the stimulus. A reverse counterconditioning effect was obtained since pairing food with CS exposures, rather than adding to the effect of CS exposure, significantly attenuated the facilitative effects of exposure on fear reduction seen when food and exposure were unpaired. This finding is consistent with a recent experiment (Delprato, 1973a) in which treatment consisting of an animal analogue to Wolpe’s systematic desensitization, of which counterconditioning is a component, was less effective in eliminating avoidance than graded or nongraded exposure alone. Delprato’s interpretation, subsequently supported (Delprato, 1973b), was that presentation of salient stimuli such as food during exposure attenuates S’s reception of the nominal stimulus. This view is consistent with Nelson’s (1966) research from which we can infer that in order to obtain a counterconditioning effect, anxiety-competing responses must facilitate S’s exposure to the aversive stimulus.* One possible interpretation of our failure to obtain a counterconditioning effect in the present experiment might revolve around the fact that counterconditioning was carried out with nongraded exposure to the CS rather than with graded presentation of the CS. Poppen (1970), consistent with Wolpe’s application of counterconditioning to his method of systematic desensitization, found that counterconditioning with graded exposure was more effective than with nongraded exposure. The rationale underlying the use of graded exposure is that anxiety-competing responses are more likely to gain ascendancy over the anxiety that occurs to the full-blown aversive stimulus when S is introduced to the stimulus in graded steps. Graded exposure was not used in the present study since earlier observations in our laboratory, confirmed by the eating behavior of Group CC, revealed that Ss consistently eat free food in the presence of the full intensity CS. Thus insofar that graded presentations are necessary to get S to eat in the face of the CS, such presentations were not required. It would, nonetheless, be worthwhile to carry out the present procedures with graded exposure to the CS. Failure to obtain a counterconditioning effect would further support the implication of the present experiment that exposure to aversive stimuli is the primary factor in the elimination of anxiety.
EXPERIMENT
2
The above experiment with its use of the standard Estes-Skinner conditioned suppression technique focused on specific fear as opposed to generalized fear in that the stimulus controlling suppression by the end of acquisition was a discrete stimulus not a diffuse * The reduced response rate in the presence of the CS of Group CC relative to Group NF-CS may fall under the empirical phenomenon referred to as positive conditioned suppression which is defined as a decrease in the rate of ongoing operant behavior in the presence of a stimulus that has been paired with response-independent positive USs. However, suppression seems to be more likely with short CS durations and acceleration, not suppression, has b:en reported with longer CS durations such as the 2 min duration of the present experiment (Meltzer and Brahlek, 1970), a state of affairs that should have increased the likelihood of our obtaining a counterconditioning effect.
458
DENNIS
J. DELPRATO
and
DONALD
E. JACKSON
situational stimulus complex. The initial shocks in the early phase of conditioned suppression acquisition typically produce a general suppressive effect on behavior that is independent of the CS (generalized fear), thus bar pressing is suppressed during non-CS periods as well as during the CS. As acquisition (CS-shock pairings, no CS-no shock) continues, bar pressing in the absence of the CS recovers presumably because absence of the CS predicts safety (Seligman, 1968); suppression thereby comes to be controlled by the discrete CS (specific fear) that predicts shock. Seligman (1968) and others have shown that bar pressing remains suppressed if the shock is not predictable either because of a random relationship between the CS and shock or because no specific environmental stimulus is paired with shock (the total environment has aversive properties). The purpose of Experiment 2 was to determine the relative efficacy of counterconditioning and exposure-only in the reduction of generalized fear. It is possible that counterconditioning effects are more readily obtained with generalized than with specific fear, perhaps because food interferes less with S’s fitnctional exposure to a diffuse aversive situation than it does to a discrete aversive stimulus. If this is the case, food paired with exposure would be more likely to produce a counterconditioning effect rather than the reverse counterconditioning effect observed in Experiment 1. Subjects and apparatus
The 20 rats that participated in the first experiment were used; they were maintained at 80 per cent of their predeprivation weight. The apparatus of Experiment 1 was used with the exception of the white noise generators which were disconnected. Procedure Preliminary training. After the termination of Experiment 1 the 20 Ss were given a day of rest followed by 3 consecutive days of 60-min base line recovery sessions on the Vl I-min schedule. While base line response rates were uniformly high during the test phase of Experiment 1, they were still 13-17 per cent below preshock levels. The three VI sessions brought base line responding back up to 100 per cent of the preshock rates in the 20 Ss as a group. The food that was to be used in counterconditioning treatment consisted of a wet mash composed of powdered Purina chow mixed with tap water served in glass food dishes. In order that Ss would have experience with the food and food dishes prior to treatment, all Ss received their daily ration in this form in their home cage following the third VI session. Fear acquisition. All 5’s received fear conditioning on the day after the third base line recovery session. Levers were retracted and 5” was confined in the apparatus for 60 min. A total of 21 response-independent, unavoidable, nonsignalled, and inescapable 1.5 mA shocks of 0.5 set duration were administered. Intershock intervals varied unsystematically and they ranged from 1.0 to 7.0 min. All Ss received their daily ration in wet mash form one-half hr after removal from the apparatus on this day. DifSerential treatment. Treatment began 24 hr after fear acquisition. The 20 5’s were randomly divided into three treatment groups with the restriction that no group contain less than one nor more than two Ss that were in any one of the four treatment conditions of Experiment 1. Group Counterconditioning (CC, n = 7) Ss were confined in the apparatus with the lever retracted for two 1%min sessions separated by 21 min spent in the home cage. Before
TREATMENT’ OF SPEClFfC AND GENERALIZED FEAR IN RATS
453
S was placed in the apparatus for each session, the food dish containing 8 g of wet mash was placed in the end of the apparatus opposite the lever and pellet trough; the S was placed in with its mouth over the dish, Group Exposure-Only (EC& it = 6) Ss were treated the same as Group CC Ss except the food dish and mash were not present in the apparatus during the treatment sessions. Group No Exposure (NE, 12= 7) Ss were not exposed to the apparatus; they were handled to the same extent as the Ss in the other two conditions and were placed back into the home cage. Group EO and NE Ss received an amount of mash equivalent to that eaten by Group CC Ss in the home cage one-half hour after the second exposure session, or handling in the case of Group NE. Post-tveatmwt test and response measure. The effects of treatment were assessed in the final phase of the experiment which took place on the day following treatment. The response levers were again available and the VI I-min schedule was in e%xt. The test session was I hr in duration and the number of Iever presses in successive 5-min intervals was recorded. Generalized fear was inferred from the amount of suppression of lever pressing for food. Suppression was expressed as the ratio of the number of Iever presses in each 5-min interval to the response rate per 5 min in the last of the three 60-min base line recovery sessions, the session prior to fear conditioning.
RESULTS
AND DISCUSSION
The mean number of responses per 5 min in the last base line recovery session was 87.2, 89.1 and 91.5 in Groups CC, EO and NE, respectively. An analysis of variance that partitioned the between-groups variable into NE vs. combined exposure groups (CC and EO) and CC vs. EO comparisons yielded Fs < 1, undulating the groups were comparabte in response rates prior to fear conditioning. All Ss in Group CC immediately began eating when placed in the apparatus for the first of the two treatment sessions, Furthermore all Ss consumed the fuil 8 g in the first session. At the beginning of the second 15-min treatment session Ss immediately began eating again but the rate of eating slowed, suggesting satiation. All Ss ate approx. 4 of the 8 g in the second session. The 12 g of mash eaten by Group CC Ss on the treatment day, and consequently fed to Ss in the other two conditions, was sufficient to keep the body weights of all rats at the prescribed 80 per cent level for the test session. The post-treatment test data can be seen in Fig. 2 which presents the mean percentage of prc-fear co~~dit~on~ng lever pressing in the three groups over successive S-min intervals. The impressive exposure effect revealed in a ~orn~arjson of Group EO and Group NE in the first 5 min attests to the powerful effects of exposure alone in the elimination of generalized fear under the present conditions. While Group NE responded at 56 per cent of its base line rate, Group EO responded at 114 per cent, above base line, in the first 5 min of the test. Unfortunately exposure-only treatment was so effective that we cannot expect to obtain a counterconditioning effect. Since group differences would obviously be masked in an analysis over all 60 min of the test due to the dissipation of fear in all groups by the first 30 min, only the first 25 min were analyzed. The exposure effect was significant (NE vs. combined exposure groups, F = 5.37, p < 0.05), but the counterconditioning effect was not significant (CC vs. EO, F < 1). While the powerful exposure-only effect obviates the demonstration of a counterconditioning effect, a reverse ~ounter~o~d~tioning elect was, of course, possible. The only hint of such an effect is seen in the first 5 min, hut the difference between Group CC and Group
460
and DONALD
DENNISJ.DELPRATO
I
2
3
4
5
6
7
E.~ACHON
8
9
IO
Ill2
5 min intervals
FIG. 2. Mean percentage of baseline (pre-fear conditioning) lever pressing in post-treatment. CC = Counterconditioning, EO = Exposure-Only, NE = No Exposure.
EO at this point is probably attributable to a tendency for Group CC to be away from the lever at the onset of the post-treatment test since the food dish in treatment was so located. The food dish was placed away from the lever in treatment so that a counterconditioning effect would not have resulted from the mere tendency for Group CC 5% to be in the vicinity of the lever during the test. Considering both experiments, the robust exposure effect found in each strongly indicates that both specific and generalized fear can be overcome with forced exposure to the aversive stimulus. Since fear reductions were inferred from the active performance of a response, the present experiments avoid the interpretative problem found in experiments that infer fear reduction from S’s failure to perform a learned active avoidance response. In experiments using active avoidance as the focal behavior, there is some evidence that forced exposure may facilitate the elimination of avoidance responses but not the elimination of fear, possibly because failure to perform an active avoidance response can be the result of either too little fear or too much fear, the iatter of which leads to crouching and freezing responses that are incompatible with performance of an active response (e.g. Coulter, Riccio and Page, 1969). A counterconditioning effect was not obtained in either experiment, but a reverse counterconditioning effect was observed in Experiment 1. This latter effect, as noted earlier, is itself consistent with views that emphasize the role of exposure to aversive stimuli in fear reduction. Given the methodological shortcomings of experiments purporting to demonstrate counterconditioning effects along with findings such as those of the present experiments, it seems worthwhile to re-evaluate anxiety-competing responses such as feeding and relaxation as they contribute to the elimination of anxiety behavior. Some steps along these lines have recently been taken by human researchers such as Davison (1971), McGlynn (1973) and Vodde and Gilner (1971) who have suggested that anxiety-competing responses (and we would include graded presentations of aversive stimuli) in desensitization may be effective only insofar as they facilitate exposure. We think that future subhuman work can
TREATMENT OF SPECIFIC AND GENERALIZED Ff3AR IN RATS
461
contribute to the re-evaluation of the role of anxiety-competing responses, graded presentations, and other aspects of desensitization in eliminating behavioral effects of aversive conditioning. REFERENCES BAUM M. (1970) Extinction of avoidance responding through response prevention (flooding) in rats. Psychol, Bull. 74,27&2&l. COULTERX., Rrccro D. C. and PAGE H. A. (1969) Effects of blocking an instrumental avoidance response: Facilitated extinction but persistence of “fear”. .T. camp. physiok Psychol. 68, 377-381. DAVISONG. C. (1968) Systematic desensitization as a co~terco~ditioni~ process. J. abmrm. Psychol. 73, 91-99. DAVISON G. C. (1971) Noncontiguous presence during treatment sessions of relaxation and imaginal aversive stimuli: A reply to Nawas, Mealiea and Fishman. Behav. Therapy 2,357-360. DELPRATOD. J. (1973a) An animal analogue to systematic desensitization and elimination of avoidance. Behav. Res. & Therapy l&49-55. DELPRATOD. J. (1973b) Exposure to the aversive stimulus in an animal analogue to systematic desensitization. Behav. Res. & Therapy 11, 187-192. ESTESW. K. and SKINNERB. F. (1941) Some quantitative properties of anxiety. J. exp. Psychol. 29,390-&O. GORDON A. and BAUM M. (1971) Increased efficacy of flooding (response prevention) in rats through positive intracranial stimulation. J. camp. physiol. Psychal. 75, 68-71. MCGLYNN F. D. (1973) Graded imagination and relaxation as components of experimental desensitization. .I. nerv. & ment. Dis. in press. MELTZERD. and BRAHLE~J. A. (1970) Conditioned suppression and conditioned enhancement with the same positive UCS: An effect of CS duration. J. exp. ad. Behav. 13, 67-73. NAWASM. M., MZLALIEA W. L. and FEHMANS. T. (1971) Systematic desensitization as ~~terconditioning: A retest with adequate controls. Behav. Therapy 2, 345-356. NELSONF. (1966) Effects of two counterconditioning procedures on the extinction of fear. f. conzp. physiol. Psyehoi. 62,208-213. POPPENR. (1970) Counterconditioning of conditioned suppression in rats. Psychoi. Rep. 27, 659-671. SELIGMANM. E. P. (1968) Chronic fear produced by unpredictable electric shock. J. camp. physiol. Psychol. 66,402-411. VODDET. W. and GILNER F. H. (1971) The effects of exposure to fear stimuli on fear reduction. Beho. Res. & Therapy9,169-175. WILSONE. H. and DINSMOORJ. A. (1970) Effect of feeding on “fear” as measured by passive avoidance in rats. .I. camp. physiol. Psychol. 70,431-436. WOLPE J. (1969) The Practice of Behavior Therapy. Pergamon Press, New York.
B.R.T.
1 I/4--
COUNTERCONDITIONING AND EXPOSURE-ONLY IN THE TREATMENT OF SPECIFIC (CONDITIONED SUPPRESSION) AND GENERALIZED FEAR IN RATS* DENNIS J. DELPRATO and DONALD E. JACKSON Department of Psychology, Eastern Michigan University, Ypsilanti, Michigan 48197, U.S.A.
Summary-In Experiment 1 the conditioned suppression technique was used to condition specific fear, suppression of operant lever pressing for food to a discrete CS. The eficacy of four treatment conditions on fear reduction was evaluated. Countercondjtjoning in which exposure to the CS was ~ntiguously paired with food was significantly less effective than noncontiguous CS exposure and food. An exposure-only effect was indicated by the superiority of all three treatments involving CS exposure (the above two plus a typical conditioned suppression extinction procedure) to treatment consisting of food only. The reverse counterconditioning effect and the exposure effect are consistent with current views that emphasize the centrality of aversive stimulus exposure in fear reduction. Experiment 2 investigated elimination of generalized fear produced by unsignalled, inescapable shocks in the lever-pressing apparatus. Two treatments (counterconditioning and exposure-only) were equally effective and they were superior to no exposure csntrol treatment. The results of the two experiments reinforce recent attempts toward a reevaIuation of the role of anxiety-competing responses in elimination of fear.
COUNTERCONDITIONING, the operation of pairing stimuli that elicit anxiety/avoidance competing responses with conditioned aversive stimuli, has been used successfully by behaviorally oriented therapists in the treatment of maladaptive avoidance and fear (anxiety) behavior (e.g. Wolpe, 1969). However, the critical variables underlying the efficacy of counterconditioning have not been isolated in controlled research. Since exposure to the conditioned aversive stimuIus in the absence of primary aversive stimulation (exposure-only) is an inherent feature of counterconditioning, and given that such treatment has been shown to reduce fear and avoidance (cf. Baum, 1970), effects of coL~nterconditioning must be evaluated in comparison with exposure-only treatment conditions in which exposure and anxiety/avoidance competing responses are noncontiguous. Diminutions in fear and avoidance can be attributed to counterconditioning to the extent that counterconditioning is superior to exposure-only. Consideration of human and infrahuman experiments reveals that counterconditioning may be more effective than exposure-only in certain circumstances, although most findings are equivocal. For example, while Davison (1968) found graded exposure to aversive stimuli contiguous with anxiety-competing relaxation more effective in reducing snake avoidance in female undergraduates than graded exposure alone, Nawas, Mealiea and Fishman (1971) obtained equivalent behavior changes with contiguous and noncontiguous relaxation and exposure. At the infrahuman level, Wilson and Dinsmoor (1970) reported that exposure combined with feeding on a platform led to greater reductions in passive avoidance (fear) of a grid floor below the platform than platform exposure-only; however,
* Supported in part by Grant MH20833-01 from the National Institute of Mental Health. 453
454
DENNIS
J. DELPRATO
and EKfNAtD E.
JACKSON
counterconditioning was not more effective than ~on~ned exposure to the grid without food. Poppen (1970) used the conditioned emotional response or conditioned s~~ppression technique (Estes and Skinner, 1941) with rats and found results analogous to those of Davison (1968), i.e. graded exposure to the tonal CS contiguous with response independent (‘free’) food was superior to graded exposure-only in reducing suppression (fear) to the CS. F-fowever, Nawas et a/.‘~ (1971) criticism of Davison’s finding can be applied to Poppen’s situation in that the latter failed to include a condition with noncontiguous exposure and free food. Gordon and Baum (1971) first trained rats to perform an active avoidance response by jumping up to a ledge in an avoidance apparatus. C~unter~ollditioning treatment consisting of forced exposure to the apparatus paired with positive intra~ra~~ial stimulation (ICS) produced greater reductions in avoidance than either apparatus exposure alone, ICS in a neutral area, or exposure to a neutral area. Unf~rtui~ately Gordon and Baum’s failure to include a treatment comprised of nol~~ontiguous apparatus exposure and ICS precludes an L~nequivocaI interpretation of their results in terms of counterconditioning. Since the question of the relative efficacy of coL~nter~onditio~lillg and exposure-only in the reduction of fear has practical and theoretical impIications, the present research compared these two methods under conditiQns designed to obviate interpretative problems such as the above. In Experiment 1, the conditioned suppression paradigm was used to condition fear to a discrete stimulus (CS). The empirical measure of fear in this paradigm is the suppression of ongoing appctitive operant behavior produced by a CS that has been paired with shock. Counterconditioning consisted of response-independel~t presentations of food during the CS. Two basic control conditions included (a) ~~t~~olltiguo~ls food and CS exposure and (b) food only (no exposure). Greater reductions in suppression with count~r~ond~t~onil~g than with noncontiguous food and exposure would seem to of&r unanlbigLlous evidence that pairing an anxiety-con~peti~~~ response with exposure (~our~terconditioning} adds to whatever effects exposure per se has. Comparison of the two exposure treatments with no exposure treatment should reveal whether treatment was prolonged enough to produce an exposure effect. This latter comparison is important since failure to obtain a counterconditioning effect could be the result of an insufficient number of treatment trials, in which case even an exposure effect may not be obtained. On the other hand, if treatment is sufficient to produce an exposure effect, it seems more likely that treatment has been prolonged enough to allow a ~oLlnter~onditioniilg effect to operate.
The 5’s were 20 nai’ve male albino rats {,Sprague-Daw~e}~) obtained from Spartan Research Animals, Haslett, Michigan. They were individually caged under constant illumination with free access to water. At the beginning of experimentation, weights ranged from 300 to 356 g, with a mean of 332 g. Restricted feedings of Purina Rat Chow reduced weights to 80 per cent of predeprivation weight, a level maintained throughout the experiment. Ali testing was done in IO identical 30.5 x 24 x 27 cm Lehigh Valley Electronics duafbar rat chambers (right lever permanently retracted). The Aoor of each chamber was constructed of 0.48 cm dia. stainless steel rods, 1.90 cm apart center to center. Each chamber was enclosed in a blower-ventilated, s~~ind-attenuating chest located in a separate cubicle. Each unit was equipped with a speaker mounted on the wali of the chest 30 cm from the lever, print-out counter, Model 113-04 Lehigh Valley shocker-scrambler, and solid state
TREATMENT
OF SPECIFKC AND GENERALfZED
FEAR fN RATS
455
control modules. Reinforcement (45..mg Noyes pellets) availability and CS presentations were controlled from a central source in an adjacent room. The CS was a 2-min white noise produced by two Grason-Stadler noise generators (Model 901s). Each generator served five chambers. Noise level readings (X0 dB & 1 re 0.0002 dynes/cm2) were taken at the response lever. The US was a 0.5 set, 1.5 mA shock.
Procedure Pr~~i~~?i~~ar~~ tmkiq. On the first day, Ss self-trained to a criterion of 50 reinfor~ments CRF. Shaping was used where necessary. The following day, Vi I-min training began and consisted of five I-hr sessions over 3 days. Fear ~~~~i~s~tioi~.The next day, two five-trial fear conditioning sessions were held while Ss responded on the VI schedule. In the morning, five 2-min CSs were given with the shock US delivered as each CS terminated. CS onsets occurred at 6, 16, 24, 33 and 41 min into the 45 min session. In the afternoon, CS onsets occurred at 7, 16,23,33.5 and 42 min into the 45 min session. The next morning, two additional fear conditioning trials were given with CS onsets at 10 and 30 min into the 35min session. Shock was not used for the remainder of the experiment. Dijkrcntial treatment. On the day following the last fear conditioning trial, Ss were randomly assigned to one of four groups (12 = 5 per group) for differential treatment, Group Normal Extinction (NExt) Ss had the response Iever available with food responsecontingent on the original VI schedule, This group, the onfy group with access to the Iever in treatment, was included to permit monitoring of suppression throughout treatment and as a typical conditioned suppression extinction conditiol~ with which the other treatments could be compared. Group Co~lnterconditioning {CC) Ss had the lever retracted and received 15 “free” pehets during each of six 2-min CS presentations. The 1.5 pellets were unsystematically spaced during each CS. Group Nonconti~uoLls Food and CS exposure (NF-CS) Ss had the lever retracted and received 15 free pellets during each of six post-CS (nor&S) periods. The 2-min non-CS intervals for Group NF-CS began from 1 to 3 min after termination of the previous CS and terminated 2-4 min prior to the next CS onset. Group No Exposure, Food-Only (FO) Ss received treatment identical with that of Group CC except the CS was never presented; food was presented to FO Ss at the same time it was presented to Group CC Ss, Thus all groups except NExt received 90 free pellets and all groups except FU received six 2-min CS exposures in treatment. The CS exposure groups had CS onsets at 6, 15, 25, 33,43 and 51 min into the 57-min session. Onsets of the six 2-min nor&S periods (Group NF-CS) were 10, 20, 29, 37, 46 and 54 min into the session. Post-tr~~t~e~t test. On the day following treatment ah Ss received six 2-min CS presentations at 6, 12, 21, 29, 36 and 46 min into the 50-min session, The lever was avaifable with food response-contingent on the original VI I-min schedule. Index of suppression. CS effects on bar pressing were assessed by the commonly used suppression ratio, B/(A + El), where B represents the number of responses emitted during the 2-min CS and A refers to the number of responses emitted during the 2-min period immediately prior to CS onset. A ratio of 0.50 indicates no CS effect while a ratio of O,oO indicates complete CS-produced suppression. Ratios for each S were computed for each trial during fear acquisition and the post-treatment test and for NExt Ss during treatment.
456
DENNIS J. DELPRATO
RESULTS
and DONALD
E. JACKSON
AND DISCUSSION
Fear acquisition and d@erential treatment Conditioned suppression to the discrete CS was rapidly acquired in a comparable manner in the four groups. Mean suppression ratios in the various groups ranged from 0.00 to 0.07 on Trial 6 and from 0.00 to 0.02 on the last trial. An analysis of variance of the acquisition scores indicated the groups were statistically equivalent prior to differential treatment (F= 1.13). Mean suppression ratios of Group NExt over the six extinction trials in treatment were 0.01, 0.02, 0.07, 0.14, 0.27 and 0.27, respectively. All Ss in Group NExt showed an increase in their ratios from the first to the last trial, indicating extinction of suppression. The eating behavior of Ss in the three groups that received free pellets in treatment was observed and latency to begin eating upon receipt of the first pellet of each series of 15 pellets was measured with a stopwatch. The median latencies to eat on the first series were 2, 2 and 4 for Groups CC, NF-CS, and FO, respectively. While one S in Group CC did not eat in the presence of the CS on the first series, it promptly began eating upon termination of the CS. On only one other occasion did a CC rat not eat in the presence of the CS. Aside from these two episodes, there appears to be no other way in which the group with the CS present during food presentation (Group CC) differed either quantitatively or qualitatively from the groups with CS absent during food presentation (Groups NF-CS and FO) in responsiveness to the food.
FO I I
I 2
I 3
I 4
I 5
I 6
Trio1
FIG. 1. Mean suppression ratios of the four treatment groups in post-treatment. CC r= Counterconditioning, NF-CS = Noncontiguous Food and CS exposure, FO = Food Only, NExt = Normal Extinction.
Post-treatment test. Mean suppression ratios over the six trials in post-treatment are shown in Fig. 1. The results are not consistent with the suggestion that contiguous pairing of aversive stimulus exposure and food is more effective in reducing fear than noncontiguous presentation of food and exposure since Group CC was more suppressed throughout the test than was Group NF-CS. The basic analysis of the data involved partitioning the treatment variable into two independent components which enabled comparison of the three CS exposure grouIjs (NExt, CC and NF-CS) with the nonexposure condition (FO) and of
TREATMENT
OF SPECIFIC
AND GENERALIZED
FEAR IN RATS
457
NExt vs. CC vs. NF-CS. The analysis yielded a significant effect for the nonexposure vs. combined exposure comparison over all test trials (t; = 10.26, p < 0.01). The F-value for between-group variation among the three exposure groups fell short of significance at the 0.05 level (F = 3.02, p < 0.10); however, individual comparisons via Duncan’s Multiple Range Test indicated that Group CC was significantly more suppressed than Group NFCS. Group NExt differed from neither Group NF-CS nor Group CC (p > 0.05). The main finding of this experiment was that exposure to the aversive stimulus, whether paired or unpaired with food and eating, was sufficient to reduce the acquired fear-eliciting capacity of the stimulus. A reverse counterconditioning effect was obtained since pairing food with CS exposures, rather than adding to the effect of CS exposure, significantly attenuated the facilitative effects of exposure on fear reduction seen when food and exposure were unpaired. This finding is consistent with a recent experiment (Delprato, 1973a) in which treatment consisting of an animal analogue to Wolpe’s systematic desensitization, of which counterconditioning is a component, was less effective in eliminating avoidance than graded or nongraded exposure alone. Delprato’s interpretation, subsequently supported (Delprato, 1973b), was that presentation of salient stimuli such as food during exposure attenuates S’s reception of the nominal stimulus. This view is consistent with Nelson’s (1966) research from which we can infer that in order to obtain a counterconditioning effect, anxiety-competing responses must facilitate S’s exposure to the aversive stimulus.* One possible interpretation of our failure to obtain a counterconditioning effect in the present experiment might revolve around the fact that counterconditioning was carried out with nongraded exposure to the CS rather than with graded presentation of the CS. Poppen (1970), consistent with Wolpe’s application of counterconditioning to his method of systematic desensitization, found that counterconditioning with graded exposure was more effective than with nongraded exposure. The rationale underlying the use of graded exposure is that anxiety-competing responses are more likely to gain ascendancy over the anxiety that occurs to the full-blown aversive stimulus when S is introduced to the stimulus in graded steps. Graded exposure was not used in the present study since earlier observations in our laboratory, confirmed by the eating behavior of Group CC, revealed that Ss consistently eat free food in the presence of the full intensity CS. Thus insofar that graded presentations are necessary to get S to eat in the face of the CS, such presentations were not required. It would, nonetheless, be worthwhile to carry out the present procedures with graded exposure to the CS. Failure to obtain a counterconditioning effect would further support the implication of the present experiment that exposure to aversive stimuli is the primary factor in the elimination of anxiety.
EXPERIMENT
2
The above experiment with its use of the standard Estes-Skinner conditioned suppression technique focused on specific fear as opposed to generalized fear in that the stimulus controlling suppression by the end of acquisition was a discrete stimulus not a diffuse * The reduced response rate in the presence of the CS of Group CC relative to Group NF-CS may fall under the empirical phenomenon referred to as positive conditioned suppression which is defined as a decrease in the rate of ongoing operant behavior in the presence of a stimulus that has been paired with response-independent positive USs. However, suppression seems to be more likely with short CS durations and acceleration, not suppression, has b:en reported with longer CS durations such as the 2 min duration of the present experiment (Meltzer and Brahlek, 1970), a state of affairs that should have increased the likelihood of our obtaining a counterconditioning effect.
458
DENNIS
J. DELPRATO
and
DONALD
E. JACKSON
situational stimulus complex. The initial shocks in the early phase of conditioned suppression acquisition typically produce a general suppressive effect on behavior that is independent of the CS (generalized fear), thus bar pressing is suppressed during non-CS periods as well as during the CS. As acquisition (CS-shock pairings, no CS-no shock) continues, bar pressing in the absence of the CS recovers presumably because absence of the CS predicts safety (Seligman, 1968); suppression thereby comes to be controlled by the discrete CS (specific fear) that predicts shock. Seligman (1968) and others have shown that bar pressing remains suppressed if the shock is not predictable either because of a random relationship between the CS and shock or because no specific environmental stimulus is paired with shock (the total environment has aversive properties). The purpose of Experiment 2 was to determine the relative efficacy of counterconditioning and exposure-only in the reduction of generalized fear. It is possible that counterconditioning effects are more readily obtained with generalized than with specific fear, perhaps because food interferes less with S’s fitnctional exposure to a diffuse aversive situation than it does to a discrete aversive stimulus. If this is the case, food paired with exposure would be more likely to produce a counterconditioning effect rather than the reverse counterconditioning effect observed in Experiment 1. Subjects and apparatus
The 20 rats that participated in the first experiment were used; they were maintained at 80 per cent of their predeprivation weight. The apparatus of Experiment 1 was used with the exception of the white noise generators which were disconnected. Procedure Preliminary training. After the termination of Experiment 1 the 20 Ss were given a day of rest followed by 3 consecutive days of 60-min base line recovery sessions on the Vl I-min schedule. While base line response rates were uniformly high during the test phase of Experiment 1, they were still 13-17 per cent below preshock levels. The three VI sessions brought base line responding back up to 100 per cent of the preshock rates in the 20 Ss as a group. The food that was to be used in counterconditioning treatment consisted of a wet mash composed of powdered Purina chow mixed with tap water served in glass food dishes. In order that Ss would have experience with the food and food dishes prior to treatment, all Ss received their daily ration in this form in their home cage following the third VI session. Fear acquisition. All 5’s received fear conditioning on the day after the third base line recovery session. Levers were retracted and 5” was confined in the apparatus for 60 min. A total of 21 response-independent, unavoidable, nonsignalled, and inescapable 1.5 mA shocks of 0.5 set duration were administered. Intershock intervals varied unsystematically and they ranged from 1.0 to 7.0 min. All Ss received their daily ration in wet mash form one-half hr after removal from the apparatus on this day. DifSerential treatment. Treatment began 24 hr after fear acquisition. The 20 5’s were randomly divided into three treatment groups with the restriction that no group contain less than one nor more than two Ss that were in any one of the four treatment conditions of Experiment 1. Group Counterconditioning (CC, n = 7) Ss were confined in the apparatus with the lever retracted for two 1%min sessions separated by 21 min spent in the home cage. Before
TREATMENT’ OF SPEClFfC AND GENERALIZED FEAR IN RATS
453
S was placed in the apparatus for each session, the food dish containing 8 g of wet mash was placed in the end of the apparatus opposite the lever and pellet trough; the S was placed in with its mouth over the dish, Group Exposure-Only (EC& it = 6) Ss were treated the same as Group CC Ss except the food dish and mash were not present in the apparatus during the treatment sessions. Group No Exposure (NE, 12= 7) Ss were not exposed to the apparatus; they were handled to the same extent as the Ss in the other two conditions and were placed back into the home cage. Group EO and NE Ss received an amount of mash equivalent to that eaten by Group CC Ss in the home cage one-half hour after the second exposure session, or handling in the case of Group NE. Post-tveatmwt test and response measure. The effects of treatment were assessed in the final phase of the experiment which took place on the day following treatment. The response levers were again available and the VI I-min schedule was in e%xt. The test session was I hr in duration and the number of Iever presses in successive 5-min intervals was recorded. Generalized fear was inferred from the amount of suppression of lever pressing for food. Suppression was expressed as the ratio of the number of Iever presses in each 5-min interval to the response rate per 5 min in the last of the three 60-min base line recovery sessions, the session prior to fear conditioning.
RESULTS
AND DISCUSSION
The mean number of responses per 5 min in the last base line recovery session was 87.2, 89.1 and 91.5 in Groups CC, EO and NE, respectively. An analysis of variance that partitioned the between-groups variable into NE vs. combined exposure groups (CC and EO) and CC vs. EO comparisons yielded Fs < 1, undulating the groups were comparabte in response rates prior to fear conditioning. All Ss in Group CC immediately began eating when placed in the apparatus for the first of the two treatment sessions, Furthermore all Ss consumed the fuil 8 g in the first session. At the beginning of the second 15-min treatment session Ss immediately began eating again but the rate of eating slowed, suggesting satiation. All Ss ate approx. 4 of the 8 g in the second session. The 12 g of mash eaten by Group CC Ss on the treatment day, and consequently fed to Ss in the other two conditions, was sufficient to keep the body weights of all rats at the prescribed 80 per cent level for the test session. The post-treatment test data can be seen in Fig. 2 which presents the mean percentage of prc-fear co~~dit~on~ng lever pressing in the three groups over successive S-min intervals. The impressive exposure effect revealed in a ~orn~arjson of Group EO and Group NE in the first 5 min attests to the powerful effects of exposure alone in the elimination of generalized fear under the present conditions. While Group NE responded at 56 per cent of its base line rate, Group EO responded at 114 per cent, above base line, in the first 5 min of the test. Unfortunately exposure-only treatment was so effective that we cannot expect to obtain a counterconditioning effect. Since group differences would obviously be masked in an analysis over all 60 min of the test due to the dissipation of fear in all groups by the first 30 min, only the first 25 min were analyzed. The exposure effect was significant (NE vs. combined exposure groups, F = 5.37, p < 0.05), but the counterconditioning effect was not significant (CC vs. EO, F < 1). While the powerful exposure-only effect obviates the demonstration of a counterconditioning effect, a reverse ~ounter~o~d~tioning elect was, of course, possible. The only hint of such an effect is seen in the first 5 min, hut the difference between Group CC and Group
460
and DONALD
DENNISJ.DELPRATO
I
2
3
4
5
6
7
E.~ACHON
8
9
IO
Ill2
5 min intervals
FIG. 2. Mean percentage of baseline (pre-fear conditioning) lever pressing in post-treatment. CC = Counterconditioning, EO = Exposure-Only, NE = No Exposure.
EO at this point is probably attributable to a tendency for Group CC to be away from the lever at the onset of the post-treatment test since the food dish in treatment was so located. The food dish was placed away from the lever in treatment so that a counterconditioning effect would not have resulted from the mere tendency for Group CC 5% to be in the vicinity of the lever during the test. Considering both experiments, the robust exposure effect found in each strongly indicates that both specific and generalized fear can be overcome with forced exposure to the aversive stimulus. Since fear reductions were inferred from the active performance of a response, the present experiments avoid the interpretative problem found in experiments that infer fear reduction from S’s failure to perform a learned active avoidance response. In experiments using active avoidance as the focal behavior, there is some evidence that forced exposure may facilitate the elimination of avoidance responses but not the elimination of fear, possibly because failure to perform an active avoidance response can be the result of either too little fear or too much fear, the iatter of which leads to crouching and freezing responses that are incompatible with performance of an active response (e.g. Coulter, Riccio and Page, 1969). A counterconditioning effect was not obtained in either experiment, but a reverse counterconditioning effect was observed in Experiment 1. This latter effect, as noted earlier, is itself consistent with views that emphasize the role of exposure to aversive stimuli in fear reduction. Given the methodological shortcomings of experiments purporting to demonstrate counterconditioning effects along with findings such as those of the present experiments, it seems worthwhile to re-evaluate anxiety-competing responses such as feeding and relaxation as they contribute to the elimination of anxiety behavior. Some steps along these lines have recently been taken by human researchers such as Davison (1971), McGlynn (1973) and Vodde and Gilner (1971) who have suggested that anxiety-competing responses (and we would include graded presentations of aversive stimuli) in desensitization may be effective only insofar as they facilitate exposure. We think that future subhuman work can
TREATMENT OF SPECIFIC AND GENERALIZED Ff3AR IN RATS
461
contribute to the re-evaluation of the role of anxiety-competing responses, graded presentations, and other aspects of desensitization in eliminating behavioral effects of aversive conditioning. REFERENCES BAUM M. (1970) Extinction of avoidance responding through response prevention (flooding) in rats. Psychol, Bull. 74,27&2&l. COULTERX., Rrccro D. C. and PAGE H. A. (1969) Effects of blocking an instrumental avoidance response: Facilitated extinction but persistence of “fear”. .T. camp. physiok Psychol. 68, 377-381. DAVISONG. C. (1968) Systematic desensitization as a co~terco~ditioni~ process. J. abmrm. Psychol. 73, 91-99. DAVISON G. C. (1971) Noncontiguous presence during treatment sessions of relaxation and imaginal aversive stimuli: A reply to Nawas, Mealiea and Fishman. Behav. Therapy 2,357-360. DELPRATOD. J. (1973a) An animal analogue to systematic desensitization and elimination of avoidance. Behav. Res. & Therapy l&49-55. DELPRATOD. J. (1973b) Exposure to the aversive stimulus in an animal analogue to systematic desensitization. Behav. Res. & Therapy 11, 187-192. ESTESW. K. and SKINNERB. F. (1941) Some quantitative properties of anxiety. J. exp. Psychol. 29,390-&O. GORDON A. and BAUM M. (1971) Increased efficacy of flooding (response prevention) in rats through positive intracranial stimulation. J. camp. physiol. Psychal. 75, 68-71. MCGLYNN F. D. (1973) Graded imagination and relaxation as components of experimental desensitization. .I. nerv. & ment. Dis. in press. MELTZERD. and BRAHLE~J. A. (1970) Conditioned suppression and conditioned enhancement with the same positive UCS: An effect of CS duration. J. exp. ad. Behav. 13, 67-73. NAWASM. M., MZLALIEA W. L. and FEHMANS. T. (1971) Systematic desensitization as ~~terconditioning: A retest with adequate controls. Behav. Therapy 2, 345-356. NELSONF. (1966) Effects of two counterconditioning procedures on the extinction of fear. f. conzp. physiol. Psyehoi. 62,208-213. POPPENR. (1970) Counterconditioning of conditioned suppression in rats. Psychoi. Rep. 27, 659-671. SELIGMANM. E. P. (1968) Chronic fear produced by unpredictable electric shock. J. camp. physiol. Psychol. 66,402-411. VODDET. W. and GILNER F. H. (1971) The effects of exposure to fear stimuli on fear reduction. Beho. Res. & Therapy9,169-175. WILSONE. H. and DINSMOORJ. A. (1970) Effect of feeding on “fear” as measured by passive avoidance in rats. .I. camp. physiol. Psychol. 70,431-436. WOLPE J. (1969) The Practice of Behavior Therapy. Pergamon Press, New York.
B.R.T.
1 I/4--