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Efficacy of response prevention (flooding) in facilitating the extinction of an avoidance response in rats: The effect of overtraining the response
Behav.Res. &Therapy, 1968,Vol. 6. pp. 197to 203. PergamonPress. Printedin England
EFFICACY OF RESPONSE PREVENTION (FLOODING) IN FACILITATING THE EXTINCTION OF AN AVOIDANCE RESPONSE IN RATS: THE EFFECT OF OVERTRAINING THE RESPONSE MOKRIE BAUM Department
of Psychology,
McGill University, Montreal, Canada
(Recei~,ed 20 October 1967) Summaty-Ninety tats were trained to avoid shock. When Ss had achieved the learning criterion, they were assigned to one of three groups, which received 0, 50 or 100 overtraining trials. Following the completion of overtraining, a response-prevention (flooding) treatment was administered to all groups. (Response prevention consisted of thwarting the avoidance response white forcing S to remain in the presence of the feared stimulus). Ss which made at least one error during overtraining (be it 50 or 100 trials) made mote avoidance responses in an extinction session following response prevention than did the group which received no overtraining. Ss which displayed perfect, 100 pet cent avoidance during overtraining made fewer avoidance responses in extinction than the no-overtraining group. THE MARKED
resistance to extinction of avoidance responding has been demonstrated many times (see Sheffield and Temmer, 1950; Sidman, 1955). Considerable attention has been devoted, to the development of experimental procedures which can facilitate the extinction of avoidance responding in animals, perhaps because this problem is so similar to that of eliminating neurotic, anxiety-motivaied behaviour in man. One such procedure is “response prevention” or “flooding” (Polin, 1959), and it consists of forcing the animal to remain in the presence of something which it fears while avoidance responses are prevented or blocked. Unlike “desensitization therapy” (Wolpe, 1958), where exposure to the fear stimulus or object is gradual and through progressive steps, response prevention ‘“floods” the animal with the furl-strength fear stimulus for a protracted period of time. The mode of action of response prevention has been variously ascribed to the learning of competing responses to the fear stimulus or object during the forced exposure to the stimulus in response prevention (Page, 1955) or to the Pavlovian extinction of classically conditioned fear (Baum, 1966). While it has been shown to hasten the extinction of an avoidance response (see Baum, 1966), there have been instances where response prevention has been relatively ineffective (see Benline and Simmel, 1967). Furthermore, the efficacy of flooding in behaviour therapy has recently been questioned (Rachman, 1966). The present study is the second in a series designed to elucidate what factors determine the ef3icacy of response prevention (flooding) in facilitating the extinction of an avoidance response in rats. This experiment investigated the effect of giving rats overtraining trials after they had acquired a readily-learned avoidance response. The basic question asked was: does overtraining make an avoidance response more or less susceptible to elimination by means of response prevention? 197
198
MORRIE
BAUM
METHOD Subjects The Ss were 90 female albino rats of the Sprague-Dawley strain. They were obtained from the Ho&man Company, Madison, Wisconsin. U.S.A. At the time the rats were avoidance trained, they were 95-120 days old and weighed 180-280 g. Apparatus The apparatus used was entireIy automated and was the same as that described extensivefy in previous studies (Baum, 1965, 1966). Briefly, it consisted of a large plywood box fitted with a grid floor through which scrambled electric shock could be administered (115 volts a.c. through a 100 kQ resistor in series with S). Into one side of the cube-shaped box projected a 23 in. wide safety Iedge. The rat could escape or avoid shock by jumping or climbing onto the ledge, where its presence was detected by a photocell system. The safety ledge was automatically retractable (via an electric motor device), and a quick retraction of the ledge resulted in the rat falling to the grid floor (see Baum, 1965 or 1966). Procedure The procedure
involved
5 phases.
Stage I: Avoidance training. Without prior habituation to the apparatus, the rat was dropped onto the grid floor via the sliding ceiling of the apparatus. Ten set after S landed on the grid, the grid was electrified and S received foot-shock until it escaped by jumping or climbing onto the safety ledge. The rat remained on the ledge for 45 set (the fixed inter-trial interval), at the end of which the ledge was automatically retracted and the rat fell to the grid floor, thus initiating the next trial. The interval available for avoiding was 10 set throughout, i.e. S could avoid shock by jumping or climbing back onto the Iedge within 10 set of being knocked down. The rats were trained until they reached an avoidance learning criterion of IO consecutive avoidance responses. Infrequently, Ss would accidentally fall off the ledge during the 45-set inter-trial interval. When an S fell down in this way, it automatically presented itself with the next trial. The timing equipnlent (a tape timer) was wired so that if S had been on the ledge for “X” set prior to failing off, then its inter-trial interval after the self-presented trial was 45-X sec. Stage 2. ~vertrain~~~. When each of the 90 Ss had achieved the learning criterion, it was assigned to one of three different overtraining groups, each having an n = 30. Each S in Group 100 received 100 additional overtraining trials following the tenth consecutive avoidance response, with the overtraining trials being identical in all respects to the training trials. Group 50 Ss received 50 overtraining trials, while Group 0 received none. Stage 3. Response Prevention. Immediately after completing the appropriate number of overtraining trials, each S in all groups was forced to spend a 5 min interval on the grid floor (presence on the grid floor being the effective fear stimulus for these Ss). To prevent any avoidance responses from occurring during this interval, the safety ledge was manually Thus, response blocking was achieved, and disengaged and removed from the apparatus. the rat was forced to remain in the situation which it had learned to fear.
FACILITATING
THE EXTINCTION
OF AN AVOIDANCE
RESPONSE IN RATS
199
Stage 4. Extinction testing. After the 5-min response prevention interval had elapsed. the ledge was reintroduced into the avoidance apparatus, thus starting the first extinction trial. The extinction trials were identical to the acquisition trials except that the shocker was disconnected so that no shocks could be administered. Each of the 90 Ss was run until it had made 25 extinction responses following response prevention, or until it attained an extinction criterion of 5 consecutive minutes on the grid floor without responding (when the response was now possible). Stage 5. Spontaneous recovery testing. Some of the animals which attained the extinction criterion before making 25 responses in extinction were tested for spontaneous recovery 24 hr later. Spontaneous recovery testing consisted of dropping the rat onto the grid floor (with the shocker disconnected), with each S being run until it again reached an extinction criterion of 5 consecutive minutes on the grid floor without responding or until it made 20 extinction responses. The number of rats tested for spontaneous recovery in the various groups was as follows: Group 0- n = 11; Group 50- n = 10; Group IOOn = 6. In all groups, the remaining animals which achieved the extinction criterion following response prevention were not given spontaneous recovery testing; instead they were used for another experiment at this point (see Baum, 1968). RESULTS .4voidance acquisition. Acquisition was very similar across the three groups, and there were no significant differences between them. (The groups were compared, two at a a time, by means of the Median test (Siegel, 1956) applied to three acquisition measures; number of trials to the first avoidance, number of trials to criterion, and number of shocks received). Groups 0, 50, and 100 required means of 1.8, 1.8, and 1.7 trials respectively to the first avoidance response; means of 2.9, 3.6, and 3.1 trials to criterion; means of 2.1, 2.3, and 2.2 shocks received (errors) to criterion. Thus, acquisition of the avoidance response was similar for all groups and substantiated previous findings (Baum, 1965, 1966) that learning was extremely rapid using this automated apparatus and procedure. Overtraining. During overtraining, 15 of the 30 Ss in Group 50 avoided perfectly and thus did not receive any additional shocks during the 50 overtraining trials. For Group 100, only 8 of the 30 Ss avoided perfectly during the overtraining trials. In both groups, the remaining Ss which failed to avoid during overtraining typically did so only once and thus only received one additional shock (which they escaped), regardless of whether overtraining consisted of 50 or 100 trials. Response prevention. Observation of the Ss during response prevention indicated that the rat generally goes through several steps when it is forced to remain on the feared grid floor with the safety ledge unavailable. Initially, abortive avoidance behaviour is displayed, characterized by rearing and frantic searching for the safety ledge and occasional upward leaps which cause the rat to strike the ceiling of the avoidance box. After a minute or so, the rat ceases this behaviour and assumes a more or less fixed posture in the box (“freezing”). This inactivity gradually gives way to exploratory behaviour characterized by locomotion about the box, rearing and sniffing at strange corners or the blower fan which ventilates the apparatus, etc. Interspersed with the exploratory behaviour are periods of grooming.
200
MORRIE
BAUM
The occurrence of extensive exploratory ambulation and sniffing is a good sign that fear is lessened and that few if any avoidance responses will be made when the safety ledge is reinserted for extinction testing. If the rat has remained frozen by the end of the 5 min response-prevention period and has exhibited little “relaxation” behaviour. it is very likely to resume responding, as though nothing had intervened, when the safety ledge is returned for extinction testing. Extinction testing. The main data of this experiment are the number of responses made by Ss during the extinction testing following the response-prevention period. Group 0 rats made a mean of 9.2 responses in the 25 trials of extinction testing, while Groups 50 and 100 had means of 10-O and 13.2 responses, respectively. A Kruskal-Wallis one-way analysis of variance by ranks (Siegel, 1956) was performed on this measure, and it was found that there was no significant effect of overtraining (H= l-10, df = 2, P > 0.20). The effectiveness of the response prevention treatment would also reflect itself in the proportion of animals in each group which attained the extinction criterion within the 25 extinction trials. In Group 0, 22 of 30 Ss extinguished within 25 trials after response prevention; for Group 50 the corresponding proportion was 20 of 30, and for Group 100, only 15 of 30. However, this effect of overtraining on the proportion of Ss extinguishing was again not statistically significant (X2=3.73, df=2, P>O-10). The.above results indicate a slight, non-significant tendency for overtraining to diminish the effectiveness of response prevention in facilitating the extinction of an avoidance response. This is somewhat misleading, for if the overtraining groups are divided in two on the basis of whether or not a failure to avoid (and therefore a shock) occurred during the overtraining trials, the picture changes somewhat. Table 1 summarizes the data organized in this way. A Kruskal-Wallis one-way analysis of variance by ranks was performed on the number of responses made by the Ss in the five groups during the 25 extinction trials. Overtraining, when analyzed in this way, produced a significant effect (H= 1 l-18, df=4, P ~0.05). The effect of overtraining on the proportion of Ss extinguishing within the 25 extinction trials was also found to be significant (X2 = 15.89, df=4, P
TABLE 1. COMPARISON OF THE VARIOUS EXPERIMENTAL GROUPS ON RESISTANCE-TO-EXTINCTION OF THE AVOIDANCE RESPONSE FOLLOWING
TWO MEASURES OF THE RESPONSE PREVENTION
Group 0 (n-30)
Group SO, (n=15)
Group 50, (n=15)
Group 100, (n=22)
Group 100,r ((n=W
73.3 :d
40.0 9;
93.3 “/,
40.9 ;,,,
75.0:;
(22130)
(6115)
(14/15)
(9122)
(6/g)
15.6
6.5
Percentage of Ss reaching the extinction criterion before the 25th extinction trial. Mean number of responses extinction trials
in 25
9.2
15.8
4.2
In the name for each group, the number (0, 50, or 100) refers to the number of overtraining trials, and the subscripts “s” or “n” refer to whether at least one shock or no shocks (respectively) were received during the overtraining trials.
FACIL1TATING
THE EXTINCTION
OF AN A\rOXDANCE RESPONSE IN RATS
201
It is obvious that there is no major difference between 50 and 100 overtraining trials (except perhaps that there is a greater opportunity to make an error in the case of 100 trials) and that the efficacy of response prevention is primarily affected by whether or not an error occurred in overtraining. Consequently, for further statistical analysis, Groups 50, and 100, were combined into one group, Group OT, (overtrained Ss which received a shock). while Groups 50, and 100, were combined into another, Group OT, (overtrained Ss which received no shock on overtraining). The proportion of Ss in Group OT, which extinguished was 15/37 (40-5 %), as compared to 20123 (87.0 %) for Group OT, and 22130 (73.3 %> for Group 0. These differences are significant (X’ = f&73, df = If P to+01 ; Xz = 5-94, df = 1, P <0+02, respectively). The difference between Group 0 and Group OT, is not significant (X2=0.76, @-= 1, P >0.20). The three groups, Groups OT,, OT,, and 0 were also compared two at a time on the number of responses made during the 25 extinction trials, using the Median test. Group OT, made s~gni~cantly more responses than Group OTn(X2 = 7.05, df= 1, P < a-011, and also more than Group 0 (X2 = 5.39, d’= 1, P < 0.05). The difference between Groups OT, and 0 was also statistically significant (X2=4.40, c/f= 1, P <04k5), with Group OT, makingfenler responses in the 25 extinction trials than Group 0. To summarize the results in extinction testing: a significant effect of overtraining on the efficacy of response prevention emerged when overtrained animals were divided into those which made at least one error during overtraining and those which avoided perfectly and. so received no additional shock in overtraining. The rats which received an additional shock in overtraining were more persistent in their extinction avoidance responding and were fess susceptible to the effects of response prevention. Animafs which avoided perfectly during overtraining made fewer extinction responses than those which received no overtraining at all. Thus, overtraining either diminishes or enhances the efficacy of response prevention in facilitating the extinction of an avoidance response, depending on whether errors occur or do not occur during overtraining. Spontaneous recovery. When some of the rats which had reached the extinction criterion after getting 0, 50, or 100 overtraining trials were tested for spontaneous recovery, they made means of 1.3, 1=8, and 6*2 responses respectively, Only one rat showed complete spontaneous recovery, evidenced by 20 responses in the 20 trials of spontaneous-recovery testing, and it was in Group 100. AI1 other rats tested for recovery reachieved the extinction criterion by the 20th trial, and usually did so very early as reflected ‘by the low means. Of the total of 27 Ss tested for spontaneous recovery, 15 made no responses whatsoever but re-achieved the extinctZion criterion of 5 min on the grid without responding at all, The effect of overtraining on the spontaneous recovery of the avoidance response was not significant (H=2*74, df= 2, P >O-20, Kruskal-Wallis one-way analysis of variance by ranks).
The above results show that overtraining, in which shocks are received, strengthens the avoidance response. However, a long series of successful avoidances in overtraining weakens the response and makes it more susceptible to elimination via response prevention. This may account for the fact that Ss receiving 100 overtraining trials are not appreciably more resistant to response prevention, if at all, than those receiving only 50 overtraining
202
MORRIE BAUM
trials. Giving more trials ensures that more Ss are likely to make an error during overtraining, but it also increases the likelihood that S will have made a long run of successful avoidances at the time response prevention is administered. (This was precisely the problem encountered in some pilot animals that were given 400 overtraining trials; all Ss made at least one error, but at the 400th trial when response prevention was given, some Ss had made as many as 200 consecutive, successful avoidances. The 400 trials seemed to produce about the same net effect as 100 trials). The above discussion leads to a general suggestion for experiments in which overtraining is varied as a parameter. Rather than giving groups different numbers of overtraining trials, it seems preferable to overtrain the groups until they make a fixed number of errors. To mention a specific example, it appears more meaningful to compare two groups which have been given overtraining until making one vs. three errors, than it is to compare groups which have received 100 vs. 400 trials. It is not obvious to what extent the results of this study depend upon the specific apparatus and procedure employed. The fact that a brief period of only 5 min of response prevention is so highly effective no doubt reflects the fact that the avoidance response is rapidly acquired. Because only a mean of about 2 shocks are received in acquisition, the conditioned fear of being on the grid floor may be fragile and easily disrupted by a short period of response prevention. This might also cause one additional shock (all that was typically received in overtraining) to have a disproportionate effect. If this study had employed an apparatus and procedure that led to slow acquisition characterized by many errors (shocks received), the importance of overtraining on the efficacy of response prevention might have been diminished. The negative results obtained using flooding in treating spider phobics (Rachman, 1966) may be due to special features of the technique used (as Wilson, 1967 has suggested); in any case, there are instances where it has been successfully employed. In the treatment of snake phobics, a flooding-type procedure involving visual imagery was just as effective as the desensitization-hierarchy technique (Wolpin and Raines, 1966). Rat phobia has also been successfully eliminated in normal subjects using a flooding procedure known as “implosive therapy” (Hogan and Kirchner, 1967). The present study confirms that response prevention or flooding can be very effective in facilitating the extinction of an avoidance response in rats. This study also showed that the main effects of overtraining on the efficacy of response prevention depended upon the absence or occurrence of shock during overtraining. Studies are presently being conducted in order further to elucidate the importance of the amount, distribution, and intensity of shock received (in the absence of overtraining) upon the effectiveness of response prevention. REFERENCES BAUM M. (1965) An automated apparatus for the avoidance training of rats. P.rychol Rep. 16, 1205-1211. BAUM M. (1966) Rapid extinction of an avoidance response following a period of response prevention in the avoidance apparatus. Psychol. Rep. 18, 59-64. BAUM M. (1968) Dissociation of respondent and operant processes in avoidance learning. (Paper in prepartition). BENLINET. A. and SIMMELE. C. (1967) Effects of blocking of the avoidance response on the elimination of the conditioned fear response. Psychon. Sci. 8, 357-358. HOGANR. A. and KIRCHNERJ. H. (1967) Preliminary report of the extinction of learned fears via shortterm implosive therapy. .I. ubnorm. Psychok 72, 106-109.
FACILITATING THE EXTINCTION OF AN AVOIDANCE RESPONSE IN RATS PAGEH. A, (1955)
203
The facilitation of experimental extinction by response prevention as a function of the acquisition of a new response. J. camp. phvsiol. Psychol. 48, 14-16. POLIN A. T. (1959) The effect of flooding and physical suppression as extinction techniques on an anxietymotivated avoidance locomotor response. J. PsychoL 47, 253-255. RACHMANS. (1966) Studies in desensitization--II. Flooding. Behav. Res. & Therapy 4, l-6. SHEFFIELDF. D. and TEMWERH. W. (1950) Relative resistance to extinction of escape training and avoidance training. J. exp. Psychof. 40, 287-298. SIDMANM. (1955) On the persistence of avoidance behavior. J. abnorm. sot. Psycho/ 50, 217-220. SIEGEL S. (1956) Nonparametric statistics forthe behavioral sciencr~s. McGraw-Hill, New York, WILSONG. D. (1967) Efficacy of “flooding” procedures in desensitization of fear: a theoretical note. Behav Res. & Therapy 5, 138. WOLPEJ. (1958) Psycb~tberapy by reciprocal j~hjbjtjo/z. Stanford University Press, Stanford. WOLPINM. and RAINES3. (1966) Visual imagery, expected roles, and extinction as possible factors in reducing fear and avoidance behavior. Behav. Res. & Therapy 4, 25-37.
EFFICACY OF RESPONSE PREVENTION (FLOODING) IN FACILITATING THE EXTINCTION OF AN AVOIDANCE RESPONSE IN RATS: THE EFFECT OF OVERTRAINING THE RESPONSE MOKRIE BAUM Department
of Psychology,
McGill University, Montreal, Canada
(Recei~,ed 20 October 1967) Summaty-Ninety tats were trained to avoid shock. When Ss had achieved the learning criterion, they were assigned to one of three groups, which received 0, 50 or 100 overtraining trials. Following the completion of overtraining, a response-prevention (flooding) treatment was administered to all groups. (Response prevention consisted of thwarting the avoidance response white forcing S to remain in the presence of the feared stimulus). Ss which made at least one error during overtraining (be it 50 or 100 trials) made mote avoidance responses in an extinction session following response prevention than did the group which received no overtraining. Ss which displayed perfect, 100 pet cent avoidance during overtraining made fewer avoidance responses in extinction than the no-overtraining group. THE MARKED
resistance to extinction of avoidance responding has been demonstrated many times (see Sheffield and Temmer, 1950; Sidman, 1955). Considerable attention has been devoted, to the development of experimental procedures which can facilitate the extinction of avoidance responding in animals, perhaps because this problem is so similar to that of eliminating neurotic, anxiety-motivaied behaviour in man. One such procedure is “response prevention” or “flooding” (Polin, 1959), and it consists of forcing the animal to remain in the presence of something which it fears while avoidance responses are prevented or blocked. Unlike “desensitization therapy” (Wolpe, 1958), where exposure to the fear stimulus or object is gradual and through progressive steps, response prevention ‘“floods” the animal with the furl-strength fear stimulus for a protracted period of time. The mode of action of response prevention has been variously ascribed to the learning of competing responses to the fear stimulus or object during the forced exposure to the stimulus in response prevention (Page, 1955) or to the Pavlovian extinction of classically conditioned fear (Baum, 1966). While it has been shown to hasten the extinction of an avoidance response (see Baum, 1966), there have been instances where response prevention has been relatively ineffective (see Benline and Simmel, 1967). Furthermore, the efficacy of flooding in behaviour therapy has recently been questioned (Rachman, 1966). The present study is the second in a series designed to elucidate what factors determine the ef3icacy of response prevention (flooding) in facilitating the extinction of an avoidance response in rats. This experiment investigated the effect of giving rats overtraining trials after they had acquired a readily-learned avoidance response. The basic question asked was: does overtraining make an avoidance response more or less susceptible to elimination by means of response prevention? 197
198
MORRIE
BAUM
METHOD Subjects The Ss were 90 female albino rats of the Sprague-Dawley strain. They were obtained from the Ho&man Company, Madison, Wisconsin. U.S.A. At the time the rats were avoidance trained, they were 95-120 days old and weighed 180-280 g. Apparatus The apparatus used was entireIy automated and was the same as that described extensivefy in previous studies (Baum, 1965, 1966). Briefly, it consisted of a large plywood box fitted with a grid floor through which scrambled electric shock could be administered (115 volts a.c. through a 100 kQ resistor in series with S). Into one side of the cube-shaped box projected a 23 in. wide safety Iedge. The rat could escape or avoid shock by jumping or climbing onto the ledge, where its presence was detected by a photocell system. The safety ledge was automatically retractable (via an electric motor device), and a quick retraction of the ledge resulted in the rat falling to the grid floor (see Baum, 1965 or 1966). Procedure The procedure
involved
5 phases.
Stage I: Avoidance training. Without prior habituation to the apparatus, the rat was dropped onto the grid floor via the sliding ceiling of the apparatus. Ten set after S landed on the grid, the grid was electrified and S received foot-shock until it escaped by jumping or climbing onto the safety ledge. The rat remained on the ledge for 45 set (the fixed inter-trial interval), at the end of which the ledge was automatically retracted and the rat fell to the grid floor, thus initiating the next trial. The interval available for avoiding was 10 set throughout, i.e. S could avoid shock by jumping or climbing back onto the Iedge within 10 set of being knocked down. The rats were trained until they reached an avoidance learning criterion of IO consecutive avoidance responses. Infrequently, Ss would accidentally fall off the ledge during the 45-set inter-trial interval. When an S fell down in this way, it automatically presented itself with the next trial. The timing equipnlent (a tape timer) was wired so that if S had been on the ledge for “X” set prior to failing off, then its inter-trial interval after the self-presented trial was 45-X sec. Stage 2. ~vertrain~~~. When each of the 90 Ss had achieved the learning criterion, it was assigned to one of three different overtraining groups, each having an n = 30. Each S in Group 100 received 100 additional overtraining trials following the tenth consecutive avoidance response, with the overtraining trials being identical in all respects to the training trials. Group 50 Ss received 50 overtraining trials, while Group 0 received none. Stage 3. Response Prevention. Immediately after completing the appropriate number of overtraining trials, each S in all groups was forced to spend a 5 min interval on the grid floor (presence on the grid floor being the effective fear stimulus for these Ss). To prevent any avoidance responses from occurring during this interval, the safety ledge was manually Thus, response blocking was achieved, and disengaged and removed from the apparatus. the rat was forced to remain in the situation which it had learned to fear.
FACILITATING
THE EXTINCTION
OF AN AVOIDANCE
RESPONSE IN RATS
199
Stage 4. Extinction testing. After the 5-min response prevention interval had elapsed. the ledge was reintroduced into the avoidance apparatus, thus starting the first extinction trial. The extinction trials were identical to the acquisition trials except that the shocker was disconnected so that no shocks could be administered. Each of the 90 Ss was run until it had made 25 extinction responses following response prevention, or until it attained an extinction criterion of 5 consecutive minutes on the grid floor without responding (when the response was now possible). Stage 5. Spontaneous recovery testing. Some of the animals which attained the extinction criterion before making 25 responses in extinction were tested for spontaneous recovery 24 hr later. Spontaneous recovery testing consisted of dropping the rat onto the grid floor (with the shocker disconnected), with each S being run until it again reached an extinction criterion of 5 consecutive minutes on the grid floor without responding or until it made 20 extinction responses. The number of rats tested for spontaneous recovery in the various groups was as follows: Group 0- n = 11; Group 50- n = 10; Group IOOn = 6. In all groups, the remaining animals which achieved the extinction criterion following response prevention were not given spontaneous recovery testing; instead they were used for another experiment at this point (see Baum, 1968). RESULTS .4voidance acquisition. Acquisition was very similar across the three groups, and there were no significant differences between them. (The groups were compared, two at a a time, by means of the Median test (Siegel, 1956) applied to three acquisition measures; number of trials to the first avoidance, number of trials to criterion, and number of shocks received). Groups 0, 50, and 100 required means of 1.8, 1.8, and 1.7 trials respectively to the first avoidance response; means of 2.9, 3.6, and 3.1 trials to criterion; means of 2.1, 2.3, and 2.2 shocks received (errors) to criterion. Thus, acquisition of the avoidance response was similar for all groups and substantiated previous findings (Baum, 1965, 1966) that learning was extremely rapid using this automated apparatus and procedure. Overtraining. During overtraining, 15 of the 30 Ss in Group 50 avoided perfectly and thus did not receive any additional shocks during the 50 overtraining trials. For Group 100, only 8 of the 30 Ss avoided perfectly during the overtraining trials. In both groups, the remaining Ss which failed to avoid during overtraining typically did so only once and thus only received one additional shock (which they escaped), regardless of whether overtraining consisted of 50 or 100 trials. Response prevention. Observation of the Ss during response prevention indicated that the rat generally goes through several steps when it is forced to remain on the feared grid floor with the safety ledge unavailable. Initially, abortive avoidance behaviour is displayed, characterized by rearing and frantic searching for the safety ledge and occasional upward leaps which cause the rat to strike the ceiling of the avoidance box. After a minute or so, the rat ceases this behaviour and assumes a more or less fixed posture in the box (“freezing”). This inactivity gradually gives way to exploratory behaviour characterized by locomotion about the box, rearing and sniffing at strange corners or the blower fan which ventilates the apparatus, etc. Interspersed with the exploratory behaviour are periods of grooming.
200
MORRIE
BAUM
The occurrence of extensive exploratory ambulation and sniffing is a good sign that fear is lessened and that few if any avoidance responses will be made when the safety ledge is reinserted for extinction testing. If the rat has remained frozen by the end of the 5 min response-prevention period and has exhibited little “relaxation” behaviour. it is very likely to resume responding, as though nothing had intervened, when the safety ledge is returned for extinction testing. Extinction testing. The main data of this experiment are the number of responses made by Ss during the extinction testing following the response-prevention period. Group 0 rats made a mean of 9.2 responses in the 25 trials of extinction testing, while Groups 50 and 100 had means of 10-O and 13.2 responses, respectively. A Kruskal-Wallis one-way analysis of variance by ranks (Siegel, 1956) was performed on this measure, and it was found that there was no significant effect of overtraining (H= l-10, df = 2, P > 0.20). The effectiveness of the response prevention treatment would also reflect itself in the proportion of animals in each group which attained the extinction criterion within the 25 extinction trials. In Group 0, 22 of 30 Ss extinguished within 25 trials after response prevention; for Group 50 the corresponding proportion was 20 of 30, and for Group 100, only 15 of 30. However, this effect of overtraining on the proportion of Ss extinguishing was again not statistically significant (X2=3.73, df=2, P>O-10). The.above results indicate a slight, non-significant tendency for overtraining to diminish the effectiveness of response prevention in facilitating the extinction of an avoidance response. This is somewhat misleading, for if the overtraining groups are divided in two on the basis of whether or not a failure to avoid (and therefore a shock) occurred during the overtraining trials, the picture changes somewhat. Table 1 summarizes the data organized in this way. A Kruskal-Wallis one-way analysis of variance by ranks was performed on the number of responses made by the Ss in the five groups during the 25 extinction trials. Overtraining, when analyzed in this way, produced a significant effect (H= 1 l-18, df=4, P ~0.05). The effect of overtraining on the proportion of Ss extinguishing within the 25 extinction trials was also found to be significant (X2 = 15.89, df=4, P
TABLE 1. COMPARISON OF THE VARIOUS EXPERIMENTAL GROUPS ON RESISTANCE-TO-EXTINCTION OF THE AVOIDANCE RESPONSE FOLLOWING
TWO MEASURES OF THE RESPONSE PREVENTION
Group 0 (n-30)
Group SO, (n=15)
Group 50, (n=15)
Group 100, (n=22)
Group 100,r ((n=W
73.3 :d
40.0 9;
93.3 “/,
40.9 ;,,,
75.0:;
(22130)
(6115)
(14/15)
(9122)
(6/g)
15.6
6.5
Percentage of Ss reaching the extinction criterion before the 25th extinction trial. Mean number of responses extinction trials
in 25
9.2
15.8
4.2
In the name for each group, the number (0, 50, or 100) refers to the number of overtraining trials, and the subscripts “s” or “n” refer to whether at least one shock or no shocks (respectively) were received during the overtraining trials.
FACIL1TATING
THE EXTINCTION
OF AN A\rOXDANCE RESPONSE IN RATS
201
It is obvious that there is no major difference between 50 and 100 overtraining trials (except perhaps that there is a greater opportunity to make an error in the case of 100 trials) and that the efficacy of response prevention is primarily affected by whether or not an error occurred in overtraining. Consequently, for further statistical analysis, Groups 50, and 100, were combined into one group, Group OT, (overtrained Ss which received a shock). while Groups 50, and 100, were combined into another, Group OT, (overtrained Ss which received no shock on overtraining). The proportion of Ss in Group OT, which extinguished was 15/37 (40-5 %), as compared to 20123 (87.0 %) for Group OT, and 22130 (73.3 %> for Group 0. These differences are significant (X’ = f&73, df = If P to+01 ; Xz = 5-94, df = 1, P <0+02, respectively). The difference between Group 0 and Group OT, is not significant (X2=0.76, @-= 1, P >0.20). The three groups, Groups OT,, OT,, and 0 were also compared two at a time on the number of responses made during the 25 extinction trials, using the Median test. Group OT, made s~gni~cantly more responses than Group OTn(X2 = 7.05, df= 1, P < a-011, and also more than Group 0 (X2 = 5.39, d’= 1, P < 0.05). The difference between Groups OT, and 0 was also statistically significant (X2=4.40, c/f= 1, P <04k5), with Group OT, makingfenler responses in the 25 extinction trials than Group 0. To summarize the results in extinction testing: a significant effect of overtraining on the efficacy of response prevention emerged when overtrained animals were divided into those which made at least one error during overtraining and those which avoided perfectly and. so received no additional shock in overtraining. The rats which received an additional shock in overtraining were more persistent in their extinction avoidance responding and were fess susceptible to the effects of response prevention. Animafs which avoided perfectly during overtraining made fewer extinction responses than those which received no overtraining at all. Thus, overtraining either diminishes or enhances the efficacy of response prevention in facilitating the extinction of an avoidance response, depending on whether errors occur or do not occur during overtraining. Spontaneous recovery. When some of the rats which had reached the extinction criterion after getting 0, 50, or 100 overtraining trials were tested for spontaneous recovery, they made means of 1.3, 1=8, and 6*2 responses respectively, Only one rat showed complete spontaneous recovery, evidenced by 20 responses in the 20 trials of spontaneous-recovery testing, and it was in Group 100. AI1 other rats tested for recovery reachieved the extinction criterion by the 20th trial, and usually did so very early as reflected ‘by the low means. Of the total of 27 Ss tested for spontaneous recovery, 15 made no responses whatsoever but re-achieved the extinctZion criterion of 5 min on the grid without responding at all, The effect of overtraining on the spontaneous recovery of the avoidance response was not significant (H=2*74, df= 2, P >O-20, Kruskal-Wallis one-way analysis of variance by ranks).
The above results show that overtraining, in which shocks are received, strengthens the avoidance response. However, a long series of successful avoidances in overtraining weakens the response and makes it more susceptible to elimination via response prevention. This may account for the fact that Ss receiving 100 overtraining trials are not appreciably more resistant to response prevention, if at all, than those receiving only 50 overtraining
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trials. Giving more trials ensures that more Ss are likely to make an error during overtraining, but it also increases the likelihood that S will have made a long run of successful avoidances at the time response prevention is administered. (This was precisely the problem encountered in some pilot animals that were given 400 overtraining trials; all Ss made at least one error, but at the 400th trial when response prevention was given, some Ss had made as many as 200 consecutive, successful avoidances. The 400 trials seemed to produce about the same net effect as 100 trials). The above discussion leads to a general suggestion for experiments in which overtraining is varied as a parameter. Rather than giving groups different numbers of overtraining trials, it seems preferable to overtrain the groups until they make a fixed number of errors. To mention a specific example, it appears more meaningful to compare two groups which have been given overtraining until making one vs. three errors, than it is to compare groups which have received 100 vs. 400 trials. It is not obvious to what extent the results of this study depend upon the specific apparatus and procedure employed. The fact that a brief period of only 5 min of response prevention is so highly effective no doubt reflects the fact that the avoidance response is rapidly acquired. Because only a mean of about 2 shocks are received in acquisition, the conditioned fear of being on the grid floor may be fragile and easily disrupted by a short period of response prevention. This might also cause one additional shock (all that was typically received in overtraining) to have a disproportionate effect. If this study had employed an apparatus and procedure that led to slow acquisition characterized by many errors (shocks received), the importance of overtraining on the efficacy of response prevention might have been diminished. The negative results obtained using flooding in treating spider phobics (Rachman, 1966) may be due to special features of the technique used (as Wilson, 1967 has suggested); in any case, there are instances where it has been successfully employed. In the treatment of snake phobics, a flooding-type procedure involving visual imagery was just as effective as the desensitization-hierarchy technique (Wolpin and Raines, 1966). Rat phobia has also been successfully eliminated in normal subjects using a flooding procedure known as “implosive therapy” (Hogan and Kirchner, 1967). The present study confirms that response prevention or flooding can be very effective in facilitating the extinction of an avoidance response in rats. This study also showed that the main effects of overtraining on the efficacy of response prevention depended upon the absence or occurrence of shock during overtraining. Studies are presently being conducted in order further to elucidate the importance of the amount, distribution, and intensity of shock received (in the absence of overtraining) upon the effectiveness of response prevention. REFERENCES BAUM M. (1965) An automated apparatus for the avoidance training of rats. P.rychol Rep. 16, 1205-1211. BAUM M. (1966) Rapid extinction of an avoidance response following a period of response prevention in the avoidance apparatus. Psychol. Rep. 18, 59-64. BAUM M. (1968) Dissociation of respondent and operant processes in avoidance learning. (Paper in prepartition). BENLINET. A. and SIMMELE. C. (1967) Effects of blocking of the avoidance response on the elimination of the conditioned fear response. Psychon. Sci. 8, 357-358. HOGANR. A. and KIRCHNERJ. H. (1967) Preliminary report of the extinction of learned fears via shortterm implosive therapy. .I. ubnorm. Psychok 72, 106-109.
FACILITATING THE EXTINCTION OF AN AVOIDANCE RESPONSE IN RATS PAGEH. A, (1955)
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The facilitation of experimental extinction by response prevention as a function of the acquisition of a new response. J. camp. phvsiol. Psychol. 48, 14-16. POLIN A. T. (1959) The effect of flooding and physical suppression as extinction techniques on an anxietymotivated avoidance locomotor response. J. PsychoL 47, 253-255. RACHMANS. (1966) Studies in desensitization--II. Flooding. Behav. Res. & Therapy 4, l-6. SHEFFIELDF. D. and TEMWERH. W. (1950) Relative resistance to extinction of escape training and avoidance training. J. exp. Psychof. 40, 287-298. SIDMANM. (1955) On the persistence of avoidance behavior. J. abnorm. sot. Psycho/ 50, 217-220. SIEGEL S. (1956) Nonparametric statistics forthe behavioral sciencr~s. McGraw-Hill, New York, WILSONG. D. (1967) Efficacy of “flooding” procedures in desensitization of fear: a theoretical note. Behav Res. & Therapy 5, 138. WOLPEJ. (1958) Psycb~tberapy by reciprocal j~hjbjtjo/z. Stanford University Press, Stanford. WOLPINM. and RAINES3. (1966) Visual imagery, expected roles, and extinction as possible factors in reducing fear and avoidance behavior. Behav. Res. & Therapy 4, 25-37.