Journal of Comparative and Physiological Psychology 1975, Vol. 88, No. 2, 619-627
ONE-TRIAL LEARNING AND SUPERIOR RESISTANCE TO EXTINCTION OF AUTONOMIC RESPONSES CONDITIONED TO POTENTIALLY PHOBIC STIMULI1 ARNE OHMAN,3 ANDERS ERIKSSON, AND CLAES OLOFSSON University oj Uppsala, Uppsala, Sweden Human subjects were exposed to pictures of potentially phobic (snakes) and supposedly neutral (houses) objects as conditioned stimuli (CSs) in a Pavlovian conditioning experiment with shock as unconditioned stimulus (US), and skin conductance and finger pulse volume as dependent variables. The skin conductance responses conditioned to phobic stimuli were acquired after one CS-US pairing, and showed practically no extinction, whereas the responses to neutral stimuli showed very little resistance to extinction after both 1 and 5 reinforcements. The superior resistance to extinction of the phobic condition was interpreted to be a specific associative effect. In general, the skin conductance acquisition data showed tendencies similar to those during extinction. For finger pulse volume responses, however, there were very weak conditioning effects, and no effect of stimidus.
Ever since its inception as an experimental field of investigation, the psychology of learning has been dominated by associationistic theories. A fundamental assumption within this theoretical framework has been that associations can be studied independent of the associated elements. In other words, the laws of learning have been regarded as valid without qualifications in terms of the kinds of stimuli, responses, or reinforcements involved. Recently, this "premise of equipotentiality" has been persuasively challenged by Seligman (1970), and the argument is substantiated by readings compiled by Seligman and Hager (1972). The main point in Seligman's alternative to the equipotentiality premise (Seligman, 1970; Seligman & Hager, 1972) is that learning must be viewed from a biological perspective, which is taken to imply that evolution has prepared a certain species to form some associations more easily than others. Thus, he postulates a dimension of preparedness that is defined in terms of "how degraded the input can be before that output reliably occurs which means that learning has taken place [Seligman & Hager,
1972, p. 4]," claiming that traditional learning theory has dealt only with the middle, unprepared region of the continuum. Highly prepared learning like, for instance, the acquisition of taste aversion in rats (see reviews by Garcia, McGowan, and Green, 1972, and Rozin and Kalat, 1971) is supposed to be very rapid, whereas extinction is quite slow; it is established even at' very long interstimulus intervals (ISIs); it is not mediated by cognitive activity; and it seems to be dependent upon a physiological mechanism different from that of ordinary learning (Seligman & Hager, 1972). This theory of prepared learning has been based entirely on animal data. However, starting from a suggestion by Seligman (1971) that phobias may be viewed as instances of prepared learning, Ohman, Erixon, and Lofberg (in press) attempted to test the applicability of the theory to human classical conditioning. They presented sets of pictures of snakes, human faces, and houses to human subjects, while measuring skin conductance. One group of subjects was shocked on snakes and another on either faces or houses. The 2 groups did not differ 1 The research reported in this article was sup- during 10 acquisition trials, but the subjects ported by grants to the first author from the shocked on snakes showed clear evidence of Swedish Council for Social Science Research. superior resistance to extinction. Further2 Requests for reprints should be sent to Arne more, this group was not affected by instrucOhman, Department of Psychology, University of tions about extinction, in contrast to convenUppsala, Slottsgrand 3, S-752 20 Uppsala, Sweden. 619
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A. OHMAN, A. ERIKSSON, AND C. OLOFSSON
tional electrodermal conditioning results Third, vasomotor activity measured as (e.g., Grings & Lockhart, 1963). This study, finger pulse volume changes was introduced then, lends support to Seligman's prepared as an additional dependent variable in order learning theory of phobias, and offers the to obtain more extensive information about possibility of comparing prepared and un- prepared autonomic conditioning. prepared human classical autonomic condiMETHOD tioning. The present study was planned in order to Subjects extend the results of Ohman et al. (in press), A total of 131 students attending introductory and, specifically, to study extinction after courses in psychology at the University of Uppsala different amounts of training. The hypothe- were paid to participate as subjects. There were 66 sis was that autonomic responses to phobic males and 65 females, with a mean age of 24.1 yr. stimuli should appear full blown after only (SD of 4.4 yr.). Eleven subjects were excluded beone pairing of conditioned stimulus (CS) cause of apparatus failure or experimenter error, and unconditioned stimulus (US), whereas leaving 12 groups with 10 subjects each. a number of pairings should be necessary to Apparatus establish conditioned responses to neutral Skin conductance was measured by a constimuli. stant voltage circuit (Hagfors, 1970) through BeckIn order to optimalize the conditions for man-Offner silver/silver chloride electrodes, which observing the effect of phobic stimuli, a had a diameter of 8 mm. and were enclosed in a number of modifications of the previous plastic cup filled with Beckman-Offner electrode procedure (Ohman et al., in press) were in- paste. Finger pulse volume was measured by a photoplethysmograph, set at a troduced. First, in the previous study, sets of transilluminated time constant of .1 sec. Respiration, which was stimuli were used, which implies that con- used as a control variable, was measured by a cept learning was part of the conditioning strain gage fastened around the subject's chest. procedure. In the present experiment, learn- Output from the various transducers was amplified ing was facilitated by exposing each subject and recorded on a Hewlett-Packard 7700 polygraph. Electric shock USs were delivered through to one stimulus only. Thus, there were differ- silver electrodes from a capacitor, which was ent groups of subjects given potentially charged by a stabilized dc current, whose voltage phobic and supposedly neutral stimuli. To could be manipulated. Color slides, 24 X 36 mm., were projected from avoid incidental influences unrelated to the Sawyer projector onto a milk-glass screen placed central theme of a set of phobic or neutral aapproximately 2 m. in front of the subject, which pictures, it was necessary to present different resulted in a visible picture of 38 X 56 cm. The pictures of the same type to the different exposure time was controlled by an electronic subjects in a certain group. Second, there timer, and the interval between successive exwere 3 modes of stimulus presentations, with posures, as well as between USs, was programmed a 2-channel Tandberg tape recorder, which different groups of subjects exposed to either on started the timer controlling the exposures and dispaired CS-US presentations, random non- charged the shock capacitor by activating relay contingent stimulus presentations, or CS- detectors. The visual stimuli consisted of 10 different picalone presentations. Thus, associative effects and effects of sensitization could be sepa- tures of snakes and 10 different pictures of houses. Thus, the 10 subjects in a group had 10 different rated from each other and from effects of the pictures, each subject seeing a different picture. phobic stimulus alone, in contrast to the previous study where only associative and Design sensitization effects could be differentiated. Basically, a completely randomized factorial 3 X This modification is essential, since noncon- 2 X 2 design was used. The first factor consisted tingent presentations of CS and US may be of conditioning, sensitization, and CS-alone treatsufficient to produce prepared learning ments. The second factor was phobic (snakes) vs. (houses) CSs, and the third factor was 1 (Garcia et al., 1972), thereby invalidating neutral vs. 5 reinforcements. Thus, there were 12 groups a sensitization control group as a baseline with 10 subjects each. In some analyses a trial facfor the assessment of conditioning effects. tor with repeated measurement was added.
CONDITIONING TO PHOBIC STIMULI
Procedure The subject was seated in a comfortable armchair in a room separated from the experimenter and the apparatus. He was then shown 5 pictures of snakes and 5 pictures of houses presented in randomized order, and was asked to rate each picture on a discomfort scale ranging 1-9. A second rating of the same pictures was performed after the conditioning session. The pictures used differed for different subjects, and in no case was the CS for a particular subject among the pictures he rated. The second phalanges of the subject's right first and second finger were washed with distilled water, and the skin conductance electrodes were applied with the help of adhesive electrode collars. The electric shock electrodes were taped to the dorsal side of. the right third and fourth fingers. The plethysmograph was attached to the second finger of the left hand, and the respiration strain gage was put in place around the subject's chest. The functions of the different transducers were informally explained while they were being applied. The intensity of the US was individually decided by exposing the subject to gradually increasing intensities until a sensation level defined as "definitely unpleasant but not painful" was reached. This procedure was not carried out on the 4 groups of subjects in the CS-alone treatments. The subject was instructed that he would be shown a picture a number of times, and, if he belonged to the conditioning or sensitization treatments, that a few shocks would be given. The door to the subject's room was then closed, and the subject was allowed to rest for a few minutes while the experimenter calibrated the apparatus. The duration of the picture CSs was 8 sec., and when reinforcement was given the US followed immediately at CS offset, giving an ISI of 8 sec. In the sensitization treatments, the USs were interspersed in the intervals between successive CSs according to a random schedule. Five initial habituation trials and 10 extinction trials were common for all 12 groups. For the conditioning groups, 1 or 5 reinforced acquisition trials were interspersed between the habituation and extinction phases. The sensitization groups had 1 or 5 CSs and 1 or 5 USs in the corresponding part of the experiment, and the CS-alone groups were merely given 1 or 5 CSs. Response definitions. Skin conductance multiple responses were defined according to the criteria proposed by Lockhart (1966). Thus, CS responses were scored in the interval 1-4 sec., and pre-US responses in the interval 4-9 sec., after CS onset. During extinction "post-US" responses were scored 1-4 sec. after CS offset. If more than one response occurred in an interval, the one having the most typical latency for the subject was scored. The responses were directly obtained in conductance, with micromhos as units. Finger pulse volume responses were scored ac-
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cording to the method proposed by Furedy (1968). Thus, the scoring interval was 2-10 sec. after CS onset, and the responses were expressed as percentage of volume pulse change. Trials with respiratory irregularities were excluded from further analyses. During extinction, trials were grouped in blocks of 2 trials each.
RESULTS Habituation The skin conductance responses showed a decrease over trials during the initial habituation to CS alone (F = 24.90, dj = 4/432, p < .001), as well as significantly larger responses to phobic than to neutral stimuli (F = 14.67, df = 1/108, p < .001). The groups having a shock level determined before the experiment showed larger responses than the CS-alone groups, as revealed by the main effect (F = 3.73, df = 2/108, p < .05) and follow-up Tukey tests. For finger pulse volume responses there was only a significant decrease over trials (F = 13.63, df = 4/432, p < .001). Acquisition The effects of acquisition were tested in 2 different ways. First, the first extinction trial was taken as a test trial for acquisition, and completely randomized 3 x 2 x 2 analyses of variance were carried out. Second, withinsubjects acquisition curves were examined for the subjects given 5 reinforcements, which resulted in a 5 X 3 X 2 split plot type of analysis with 10 subjects in each of the 6 groups. Tukey tests were used to further analyze significant effects. Skin conductance responses. The mean response magnitudes during the first extinction trials are shown in Table 1. Since there was no effect of the number-of-reinforcements factor, data have been collapsed over this variable. The conditioning groups exceeded the sensitization and CS-alone groups for all 3 response components. The difference between the conditioning group on the one hand and the sensitization and CS-alone groups on the other tended to be larger for the phobic stimuli, indicating better conditioning in the latter case. Table 2 shows the F ratios for the stimulus, conditioning, and
A. OHMAN, A. ERIKSSON, AND C. OLOFSSON
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TABLE 1 MEAN SKIN CONDUCTANCE (IN MMHOS) AND FINGER PULSE VOLUME RESPONSES (% VOLUME PULSE CHANGE) DURING THE FIRST EXTINCTION TRIAL AS A FUNCTION OF STIMULUS AND TREATMENTS Skin conductance Finger pulse volume Treatment
CS response
Conditioning Sensitization CS alone
Pre-US response
Post-US response
Phobic
Neutral
Phobic
Neutral
Phobic
Neutral
Phobic
Neutral
.533 .265 .045
.333 .235 .019
.342 .111
.140 .069 .008
.365 .135 .003
.222 .130 .003
.086 .074
.106 .073 .015
.014
.089
Note. Abbreviations: CS = conditioned stimulus; US = unconditioned stimulus.
Stimulus X Conditioning effects. For the CS response, the significant effect of conditioning was due to larger responses in the conditioning and sensitization groups as compared to the CS-alone groups. The tendency toward better conditioning to phobic stimuli was not significant. For the pre-US response, all 3 effects shown in Table 2 were significant. The interaction between stimulus and conditioning was due to better conditioning to phobic stimuli. Thus, the phobic conditioning groups exceeded both the phobic sensitization and CS-alone groups, which did not differ, whereas there were no significant differences between the neutral groups. Furthermore, the phobic conditioning group showed significantly larger responses than the neutral conditioning group, whereas no difference emerged between the sensitization and CS-alone groups for the 2 types of stimuli. The significant main effect
of conditioning on the post-US response, finally, was due to larger responses in the conditioning than in the sensitization and CS-alone groups. The results for the within-subjects acquisition analyses are shown in Figure 1. The CS responses were larger to phobic than to neutral stimuli, and the conditioning groups tended to exceed the sensitization and CSalone groups in response magnitude. Table 2 shows that the stimulus effect was significant, but the significant conditioning effect pertained to larger responses in the conditioning and sensitization groups as compared with the CS-alone group. In addition, the effect of trials was significant (F — 2.81, df - 4/126, p < .05), as well as the Trials X Conditioning interaction (F — 3.74, df = 8/126, p < .01), the latter being due to the initial rise in the acquisition curves for the conditioning groups as compared with the
TABLE 2 F RATIOS FOB THE STIMULUS, CONDITIONING, AND STIMULUS X CONDITIONING EFFECTS DURING ACQUISITION Between-subjects analysis Source
Skin conductance response df
Stimulus (S) Conditioning (C) S X C
1/108 2/108 2/108
CS
Pre-US
Post-US
2.02 13.52*** .97
6.52* 17.13** 3.40*
1.05 12.04*** .95
Within-subjects analysis Finger pulse volume
df
1.07 2.10 2.57
1/54 2/54 2/54
Skin conductance response CS
Pre-US
4.66* 6.40** .88
2.57 3.61* .53
Note. Abbreviations: CS = conditioned stimulus, US = unconditioned stimulus. * p < .05. ** p < .01. *** p < .001.
Finger pulse volume
3.21 1.10 .10
CONDITIONING TO PHOBIC STIMULI
be seen in Table 2 there were only very weak effects of stimulus pairing, and in no case was there any significant effect.
CS response Phobic
Neutral
0.90
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0,80 0,70
0.60 0.50 0.40 0,30 0,20 ,_ 0.10
1
2
3
4
Conditioning
5
1
2
3
4
5
*—»Sensitization •—• CS alone Pre-UCS response Neutral
Phobic
1
2
3
4
5
Acquisition trials
FIGURE 1. Skin conductance conditioned stimulus (CS) and pre-unconditioned-stimulus (preUCS) response acquisition curves for the phobic and neutral conditioning, sensitization, and CSalone groups (n = 10).
falling or flat functions for the other treatments. The pre-US responses showed tendencies similar to those of the CS response, but as shown in Table 2 only the effects of conditioning were significant. Follow-up tests showed that only the conditioning groups differed from the CS-alone groups. As was the case with the CS response, there was a Trials X Conditioning interaction (F = 5.00, df = 8/216, p < .01), which was due to the increasing trends over trials in the conditioning groups in contrast to the falling trends of the sensitization and CS-alone groups. Finger pulse volume responses. Data from the between-subjects acquisition analysis are shown in Table 1, and those from the within-subjects analysis in Table 3. As can
Extinction Separate analyses of variance with a split plot 5 x 3 x 2 x 2 design were carried out for each response measure during extinction. As before, Tukey tests were used in followups. Skin conductance responses. The mean response magnitudes for the skin conductance measures are shown in Figure 2. Since there were no effects of number of reinforcements, the data were collapsed for this factor. The results were similar for all 3 response components: There was a slow overall decrease with extinction trials, the overall responding tended to be higher to phobic than to neutral stimuli, and whereas there was an immediate and rather abrupt extinction effect in the neutral groups, the phobic conditioning groups continued to respond throughout the extinction period. The relevant statistics are given in Table 4. Follow-up tests showed that the conditioning groups differed from both the sensitization and CS-alone groups in the phobic condition, whereas no significant differences between groups emerged with the neutral stimulus. The effect of the phobic stimulus was a specific associative one, since the phobic conditioning groups exceeded the neutral conditioning groups, whereas the phobic sensitization and CSalone groups did not differ from the neutral sensitization and CS-alone groups. The TABLE 3 MEAN FINGBE PULSE VOLUME RESPONSES (% VOLUME PULSE CHANGE) DUEING ACQUISITION AND EXTINCTION Acquisition
(n = 10)
Treatment
Extinction
(» = 20)
Phobic Neutral Phobic Neutral
Conditioning Sensitization CS alone
.095 .080 .062
.066 .040 .040
.080 .064 .049
.073 .046 .033
Note. Data are collapsed over number of reinforcements. Abbreviation: CS = conditioned stimulus.
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A. OHMAN, A. ERIKSSON, AND C. OLOFSSON CS response Neutral
0,50 0.40 0,30 0,20 0,10
J 1
2
3
4
i Conditioning
5
1
2
*—* Sensitizalion
3
4
5
•—• CS alone
Pre-UCS response Phobic
0,30
Neutral
0,20 0,10
1
2
3
4
1
5
2
3
4
5
Post-UCS response Neutral
Phobic
0,30
0,30
0,20
0,20
0,10
0,10
1
2
3
4
5
1
E x t i n c t i o n trial blocks
FIOUBE 2. Skin conductance conditioned stimulus (CS), pre-unconditioned-stimulus (pre-UCS), and post-UCS response extinction functions for the phobic and neutral conditioning, sensitization, and CS-alone groups. (Data were collapsed for the number of reinforcements factor; n = 20.)
post-US response was the only one to show a genuine extinction effect since, according to the Trial X Conditioning interaction (F = 3.60, df = 8/432, p < .001), the conditioning groups tended to converge with the sensitization and CS-alone groups as a function of extinction trials. Finger pulse volume responses. The means for finger pulse volume responses collapsed over trials and number of reinforcements are shown in Table 3. The response magnitude diminished as a function of trials and there were overall differences between the different modes of stimulus presentation (see Table 4). Follow-up tests showed that the conditioning groups definitely exceeded the CS-alone groups (p < .01), and that they tended to
exceed also the sensitization groups (p < .10). Ratings of discomfort. The subject's ratings of discomfort produced by the type of stimulus he had as CS were summed over the 5 stimuli, and a difference between the ratings before and after the conditioning session was computed. Conditioning, sensitization, and CS alone were compared pairwise with t tests for phobic and neutral stimuli. The groups conditioned to snakes had a significantly higher difference than those conditioned to houses (t = 2.14, df = 18, p < .05), with means of 2.05 and .35, respectively. For sensitization and CS-alone groups there were no significant differences. DISCUSSION The present data show unequivocally that electrodermal responses conditioned to phobic stimuli are much more resistant to extinction than responses conditioned to neutral stimuli. Whereas all response components showed immediate and complete extinction in the latter case, they showed rather complete resistance to extinction in the former. This effect, furthermore, was a specific associative one, since the phobic conditioning groups differed from the phobic sensitization and CS-alone, and from all the neutral, groups. The ineffectiveness of the number-of-reinforcements factor indicates that the responses to phobic stimuli reached full resistance to extinction after TABLE 4 F RATIOS FOR THE TRIALS, STIMULUS, CONDITIONING, AND STIMULUS X CONDITIONING EFFECTS DURING EXTINCTION Skin conductance response [Source
Trials (T) Stimulus (S) Conditioning (C) S XC
df
4/432 1/108 2/108 2/108
CS
Pre-US
8.24*»* 10.06** 15.16*** 4.31*
4.66*** 8.46** 12.72*** 5.06**
PostUS
Finger pulse volume
10.27*** 5.36*** 8.14** 2.24 15.35*** 4.81** 3.91* .13
Note. Abbreviations: CS = conditioned stimulus; US unconditioned stimulus. * v < .05. ** p < .01. *** p < .001.
CONDITIONING TO PHOBIC STIMULI
only one CS-US pairing, whereas for the neutral stimuli there was no resistance to extinction even after 5 CS-US pairings. In conclusion, then, it can be stated that the expectations from prepared learning theory were fully confirmed for the extinction electrodermal data. The electrodermal acquisition data were less consistent. For the CS response, the conditioning and sensitization groups exceeded the CS-alone groups, but did not differ between themselves in either of the 2 analyses; and there was no effect of type of stimulus, although the tendency was in the direction of the hypothesis. The post-US response, too, failed to show superior conditioning to the phobic stimuli, although there were overall effects of conditioning. For the pre-US response, finally, there was a discrepancy between the results from the between- and within-subjects analyses. In the former, there was a significant conditioning effect to the phobic but not to the neutral stimuli, and, as in the case of the extinction data, this effect was specifically associative. In the within-subjects analysis, the tendencies were in the same direction, but only the overall difference between the conditioning and CS-alone groups was significant. Thus, the prepared learning hypothesis was only partially confirmed for the pre-US response and clearly disconfirmed for the CS and post-US responses. The finger pulse volume responses showed no significant effects during acquisition, and during extinction the conditioning groups exceeded only the CS-alone groups. Although it is possible to condition this response system in a single cue paradigm (Ohman, 1974b), very few conditioning trials were used in the present study, which might prevent the possibility of observing a conditioning effect. Furthermore, peripheral vasomotor changes are less sensitive to psychological impact than are electrodermal responses (Furedy & Gagnon, 1969). Therefore, the present negative findings may indicate that vasomotor responses are less sensitive than electrodermal ones, and that the situation was nonoptimal for learning, rather than being a source of evidence against the prepared learning theory.
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The results for the remaining dependent variable, the subjective ratings of discomfort, were positive to the prepared learning hypothesis. Thus, there were differences between the conditioning groups given phobic and neutral stimuli, but not between any other groups. This means that there were detectable subjective effects of the phobic conditioning procedure. Since there was very little extinction of the electrodermal responses to phobic stimuli, but rather complete disappearance of responses to neutral ones, the results from the ratings are in good agreement with those for the autonomic measure. In comparing the present results with those of the previous study (Ohman et al., in press), 3 points appear to be especially relevant. First, the objective of optimalizing the conditions for observing the effects of phobic stimuli obviously was successfully fulfilled. Thus, in the previous data, there were clear-cut effects of the phobic stimulus only on the CS responses during extinction, whereas, in the present instance, the effects were quite clear for all 3 response components during extinction, and, to a lesser extent, for the pre-US response during acquisition. Second, the very rapid extinction to the neutral CSs was of some importance to the success in demonstrating differences between phobic and neutral stimuli in both the previous and the present study. In conventional situations with tone or light CSs, about 10 trials seem to be needed for complete extinction (e.g., Ohman, 1974a; Ohman & Bohlin, 1973), whereas the responses to the supposedly neutral house stimuli disappeared instantly when the US was discontinued. Therefore, it is tempting to speculate that the so-called "neutral stimuli" in effect come from the contraprepared side of the preparedness continuum. These speculations open the possibility of turning the preparedness concept into a true dimension by comparing prepared, unprepared, and contraprepared human autonomic conditioning in the same experimental situation. Third, the conclusion regarding preparedness differed in both studies according to whether it was based on acquisition or ex-
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A. OHMAN, A. ERIKSSON, AND C. OLOFSSON
tinction data. This finding restricts the gen- from which preparedness can be predicted. erality of the preparedness concept (cf. Thus, the preparedness concept is anchored Seligman & Hager, 1972, p. 5) in demon- primarily on the dependent variable side, strating that acquisition and extinction data and from the history of psychology we know are independent, the latter fulfilling the cri- that this might be a paramount problem. terion of prepared learning, whereas the The present results, for instance, may be former does not. taken as support for the proposition that A couple of more general problems with phobias are instances of prepared learning. the preparedness concept are raised by the If they are interpreted as supporting the nopresent project. First, one may not legiti- tion that prepared learning is very slow to mately conclude that our results show that extinguish, however, the circle is completed. phobias are based on an inherited disposiThus, it appears that the theory of pretion to associate fear with certain situations. pared learning is faced with a number of imThis is clearly implied in the theory, but this portant problems. Nevertheless, it has assumption was not tested in either of the pointed out the significance of biological 2 studies, nor can it ever be directly tested context for learning, and it has suggested a in the present context. This is, in fact, a number of significant problems for empirical fundamental weakness in Seligman's theory, analysis. A more careful evaluation of the since, instead of suggesting a "resolution of theory, therefore, must wait for the accumuthe instinct-learning controversy [Seligman lation of further knowledge. & Hager, 1972, p. 1]," the preparedness conREFERENCES cept leaves us with the problem of determining the genetical or experiential basis for the Furedy, J. J. Human orienting reaction as a funcpreparedness. A monkey with a well-learned tion of electrodermal versus plethysmographic response modes and single versus alternating learning set certainly shows "preparedness" stimulus series. Journal of Experimental Psycholwhen faced with a new discrimination probogy, 1968, 77, 70-78. lem, but it is only through knowledge of the Furedy, J. J., & Gagnon, Y. Relationships between background factors that we can explain this and sensitivities of the galvanic skin reflex and behavior in terms of more complex learning two indices of peripheral vasoconstriction in man. Journal of Neurology, Neurosurgery, and Psyrather than in terms of genetical endowment. chiatry, 1969, 32,197-201. For the present data, it remains to be Garcia, J., McGowan, B. K., & Green, K. F. Bioshown that it is the content of the snake piclogical constraints on conditioning. In A. H. tures, as required by the prepared learning Black & W. F. Prokasy (Eds.), Classical conditioning II: Current research and theory. New theory, and not some abstract property such York: Appleton-Century-Crofts, 1972. as attensity, novelty, or complexity, that is W. W., & Lockhart, R. A. Effects of "anxieffective in producing the superior resistance Grings, ety-lessening" instructions and differential set deto extinction. A plausible line of reasoning is velopment on the extinction of GSR. Journal of to argue that the snake pictures for such Experimental Psychology, 1963, 66, 292-299. reasons (but cf. Klimova, 1965) provoke Hagfors, C. The galvanic skin response and its application to the group registration of psychomore orienting responding which in turn physiological processes. (Jyvaskyla Studies in gives better conditioning (cf. Ohman & Education, Psychology, and Social Research, No. Bohlin, 1973), and in this case there is no 23) Jyvaskyla, Finland: University of Jyvaskyla, need to invoke genetical-evolutionary con1970. cepts in the explanation. Such an argument Klimova, V. I. The character of the components of some orientational reactions. In L. G. Voronin, is strengthened by the observation of larger A. N. Leontiev, A. R. Luria, E. N. Sokolov, & orienting responses to phobic than to neutral O. S. Vinogradova (Eds.), Orienting reflex and stimuli during the initial habituation trials. exploratory behavior. Washington, D.C.: American Institute of Biological Sciences, 1965. A second problem with the preparedness concept is that it runs the danger of becom- Lockhart, R. A. Comments regarding multiple response phenomena in long interstimulus interval ing circular. This is so since evolution is conditioning. Psycho-physiology, 1966, 3, 108-114. open to speculative interpretations, rather Ohman, A. Orienting reactions, expectancy learnthan presenting a well-established theory ing, and conditioned responses in electrodermal
CONDITIONING TO PHOBIC STIMULI conditioning with different interstimulus inter.. vals. Biological Psychology, 1974, 1,189-200. (a) Ohman, A. The relationship between electrodermal and digital vasomotor responses in aversive classical conditioning. Biological Psychology, ..1974,2,17-31. (b) Ohman, A., & Bohlin, G. Magnitude and habituation of the orienting reaction as predictors of discriminative electrodermal conditioning. Journal of Experimental Research in Personality, 1973, 6, 293-299. Ohman, A., Erixon, G., & Lofberg, I. Phobias and preparedness: Phobic versus neutral pictures as conditioned stimuli for human autonomic re-
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sponses. Journal of Abnormal Psychology, in press. Rozin, P., & Kalat, J. Specific hungers and poison avoidance as adaptive specialization of learning. Psychological Review, 1971, 78, 459-486. Seligman, M. E. P. On the generality of the laws of learning. Psychological Review, 1970, 77, 406418. Seligman, M. E. P. Phobias and preparedness. Behavior Therapy, 1971, 2, 307-321. Seligman, M. E. P., & Hager, J. E. (Eds.) Biological boundaries of learning. New York: AppletonCentury-Crofts, 1972. (Received November 30, 1973)
ONE-TRIAL LEARNING AND SUPERIOR RESISTANCE TO EXTINCTION OF AUTONOMIC RESPONSES CONDITIONED TO POTENTIALLY PHOBIC STIMULI1 ARNE OHMAN,3 ANDERS ERIKSSON, AND CLAES OLOFSSON University oj Uppsala, Uppsala, Sweden Human subjects were exposed to pictures of potentially phobic (snakes) and supposedly neutral (houses) objects as conditioned stimuli (CSs) in a Pavlovian conditioning experiment with shock as unconditioned stimulus (US), and skin conductance and finger pulse volume as dependent variables. The skin conductance responses conditioned to phobic stimuli were acquired after one CS-US pairing, and showed practically no extinction, whereas the responses to neutral stimuli showed very little resistance to extinction after both 1 and 5 reinforcements. The superior resistance to extinction of the phobic condition was interpreted to be a specific associative effect. In general, the skin conductance acquisition data showed tendencies similar to those during extinction. For finger pulse volume responses, however, there were very weak conditioning effects, and no effect of stimidus.
Ever since its inception as an experimental field of investigation, the psychology of learning has been dominated by associationistic theories. A fundamental assumption within this theoretical framework has been that associations can be studied independent of the associated elements. In other words, the laws of learning have been regarded as valid without qualifications in terms of the kinds of stimuli, responses, or reinforcements involved. Recently, this "premise of equipotentiality" has been persuasively challenged by Seligman (1970), and the argument is substantiated by readings compiled by Seligman and Hager (1972). The main point in Seligman's alternative to the equipotentiality premise (Seligman, 1970; Seligman & Hager, 1972) is that learning must be viewed from a biological perspective, which is taken to imply that evolution has prepared a certain species to form some associations more easily than others. Thus, he postulates a dimension of preparedness that is defined in terms of "how degraded the input can be before that output reliably occurs which means that learning has taken place [Seligman & Hager,
1972, p. 4]," claiming that traditional learning theory has dealt only with the middle, unprepared region of the continuum. Highly prepared learning like, for instance, the acquisition of taste aversion in rats (see reviews by Garcia, McGowan, and Green, 1972, and Rozin and Kalat, 1971) is supposed to be very rapid, whereas extinction is quite slow; it is established even at' very long interstimulus intervals (ISIs); it is not mediated by cognitive activity; and it seems to be dependent upon a physiological mechanism different from that of ordinary learning (Seligman & Hager, 1972). This theory of prepared learning has been based entirely on animal data. However, starting from a suggestion by Seligman (1971) that phobias may be viewed as instances of prepared learning, Ohman, Erixon, and Lofberg (in press) attempted to test the applicability of the theory to human classical conditioning. They presented sets of pictures of snakes, human faces, and houses to human subjects, while measuring skin conductance. One group of subjects was shocked on snakes and another on either faces or houses. The 2 groups did not differ 1 The research reported in this article was sup- during 10 acquisition trials, but the subjects ported by grants to the first author from the shocked on snakes showed clear evidence of Swedish Council for Social Science Research. superior resistance to extinction. Further2 Requests for reprints should be sent to Arne more, this group was not affected by instrucOhman, Department of Psychology, University of tions about extinction, in contrast to convenUppsala, Slottsgrand 3, S-752 20 Uppsala, Sweden. 619
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A. OHMAN, A. ERIKSSON, AND C. OLOFSSON
tional electrodermal conditioning results Third, vasomotor activity measured as (e.g., Grings & Lockhart, 1963). This study, finger pulse volume changes was introduced then, lends support to Seligman's prepared as an additional dependent variable in order learning theory of phobias, and offers the to obtain more extensive information about possibility of comparing prepared and un- prepared autonomic conditioning. prepared human classical autonomic condiMETHOD tioning. The present study was planned in order to Subjects extend the results of Ohman et al. (in press), A total of 131 students attending introductory and, specifically, to study extinction after courses in psychology at the University of Uppsala different amounts of training. The hypothe- were paid to participate as subjects. There were 66 sis was that autonomic responses to phobic males and 65 females, with a mean age of 24.1 yr. stimuli should appear full blown after only (SD of 4.4 yr.). Eleven subjects were excluded beone pairing of conditioned stimulus (CS) cause of apparatus failure or experimenter error, and unconditioned stimulus (US), whereas leaving 12 groups with 10 subjects each. a number of pairings should be necessary to Apparatus establish conditioned responses to neutral Skin conductance was measured by a constimuli. stant voltage circuit (Hagfors, 1970) through BeckIn order to optimalize the conditions for man-Offner silver/silver chloride electrodes, which observing the effect of phobic stimuli, a had a diameter of 8 mm. and were enclosed in a number of modifications of the previous plastic cup filled with Beckman-Offner electrode procedure (Ohman et al., in press) were in- paste. Finger pulse volume was measured by a photoplethysmograph, set at a troduced. First, in the previous study, sets of transilluminated time constant of .1 sec. Respiration, which was stimuli were used, which implies that con- used as a control variable, was measured by a cept learning was part of the conditioning strain gage fastened around the subject's chest. procedure. In the present experiment, learn- Output from the various transducers was amplified ing was facilitated by exposing each subject and recorded on a Hewlett-Packard 7700 polygraph. Electric shock USs were delivered through to one stimulus only. Thus, there were differ- silver electrodes from a capacitor, which was ent groups of subjects given potentially charged by a stabilized dc current, whose voltage phobic and supposedly neutral stimuli. To could be manipulated. Color slides, 24 X 36 mm., were projected from avoid incidental influences unrelated to the Sawyer projector onto a milk-glass screen placed central theme of a set of phobic or neutral aapproximately 2 m. in front of the subject, which pictures, it was necessary to present different resulted in a visible picture of 38 X 56 cm. The pictures of the same type to the different exposure time was controlled by an electronic subjects in a certain group. Second, there timer, and the interval between successive exwere 3 modes of stimulus presentations, with posures, as well as between USs, was programmed a 2-channel Tandberg tape recorder, which different groups of subjects exposed to either on started the timer controlling the exposures and dispaired CS-US presentations, random non- charged the shock capacitor by activating relay contingent stimulus presentations, or CS- detectors. The visual stimuli consisted of 10 different picalone presentations. Thus, associative effects and effects of sensitization could be sepa- tures of snakes and 10 different pictures of houses. Thus, the 10 subjects in a group had 10 different rated from each other and from effects of the pictures, each subject seeing a different picture. phobic stimulus alone, in contrast to the previous study where only associative and Design sensitization effects could be differentiated. Basically, a completely randomized factorial 3 X This modification is essential, since noncon- 2 X 2 design was used. The first factor consisted tingent presentations of CS and US may be of conditioning, sensitization, and CS-alone treatsufficient to produce prepared learning ments. The second factor was phobic (snakes) vs. (houses) CSs, and the third factor was 1 (Garcia et al., 1972), thereby invalidating neutral vs. 5 reinforcements. Thus, there were 12 groups a sensitization control group as a baseline with 10 subjects each. In some analyses a trial facfor the assessment of conditioning effects. tor with repeated measurement was added.
CONDITIONING TO PHOBIC STIMULI
Procedure The subject was seated in a comfortable armchair in a room separated from the experimenter and the apparatus. He was then shown 5 pictures of snakes and 5 pictures of houses presented in randomized order, and was asked to rate each picture on a discomfort scale ranging 1-9. A second rating of the same pictures was performed after the conditioning session. The pictures used differed for different subjects, and in no case was the CS for a particular subject among the pictures he rated. The second phalanges of the subject's right first and second finger were washed with distilled water, and the skin conductance electrodes were applied with the help of adhesive electrode collars. The electric shock electrodes were taped to the dorsal side of. the right third and fourth fingers. The plethysmograph was attached to the second finger of the left hand, and the respiration strain gage was put in place around the subject's chest. The functions of the different transducers were informally explained while they were being applied. The intensity of the US was individually decided by exposing the subject to gradually increasing intensities until a sensation level defined as "definitely unpleasant but not painful" was reached. This procedure was not carried out on the 4 groups of subjects in the CS-alone treatments. The subject was instructed that he would be shown a picture a number of times, and, if he belonged to the conditioning or sensitization treatments, that a few shocks would be given. The door to the subject's room was then closed, and the subject was allowed to rest for a few minutes while the experimenter calibrated the apparatus. The duration of the picture CSs was 8 sec., and when reinforcement was given the US followed immediately at CS offset, giving an ISI of 8 sec. In the sensitization treatments, the USs were interspersed in the intervals between successive CSs according to a random schedule. Five initial habituation trials and 10 extinction trials were common for all 12 groups. For the conditioning groups, 1 or 5 reinforced acquisition trials were interspersed between the habituation and extinction phases. The sensitization groups had 1 or 5 CSs and 1 or 5 USs in the corresponding part of the experiment, and the CS-alone groups were merely given 1 or 5 CSs. Response definitions. Skin conductance multiple responses were defined according to the criteria proposed by Lockhart (1966). Thus, CS responses were scored in the interval 1-4 sec., and pre-US responses in the interval 4-9 sec., after CS onset. During extinction "post-US" responses were scored 1-4 sec. after CS offset. If more than one response occurred in an interval, the one having the most typical latency for the subject was scored. The responses were directly obtained in conductance, with micromhos as units. Finger pulse volume responses were scored ac-
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cording to the method proposed by Furedy (1968). Thus, the scoring interval was 2-10 sec. after CS onset, and the responses were expressed as percentage of volume pulse change. Trials with respiratory irregularities were excluded from further analyses. During extinction, trials were grouped in blocks of 2 trials each.
RESULTS Habituation The skin conductance responses showed a decrease over trials during the initial habituation to CS alone (F = 24.90, dj = 4/432, p < .001), as well as significantly larger responses to phobic than to neutral stimuli (F = 14.67, df = 1/108, p < .001). The groups having a shock level determined before the experiment showed larger responses than the CS-alone groups, as revealed by the main effect (F = 3.73, df = 2/108, p < .05) and follow-up Tukey tests. For finger pulse volume responses there was only a significant decrease over trials (F = 13.63, df = 4/432, p < .001). Acquisition The effects of acquisition were tested in 2 different ways. First, the first extinction trial was taken as a test trial for acquisition, and completely randomized 3 x 2 x 2 analyses of variance were carried out. Second, withinsubjects acquisition curves were examined for the subjects given 5 reinforcements, which resulted in a 5 X 3 X 2 split plot type of analysis with 10 subjects in each of the 6 groups. Tukey tests were used to further analyze significant effects. Skin conductance responses. The mean response magnitudes during the first extinction trials are shown in Table 1. Since there was no effect of the number-of-reinforcements factor, data have been collapsed over this variable. The conditioning groups exceeded the sensitization and CS-alone groups for all 3 response components. The difference between the conditioning group on the one hand and the sensitization and CS-alone groups on the other tended to be larger for the phobic stimuli, indicating better conditioning in the latter case. Table 2 shows the F ratios for the stimulus, conditioning, and
A. OHMAN, A. ERIKSSON, AND C. OLOFSSON
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TABLE 1 MEAN SKIN CONDUCTANCE (IN MMHOS) AND FINGER PULSE VOLUME RESPONSES (% VOLUME PULSE CHANGE) DURING THE FIRST EXTINCTION TRIAL AS A FUNCTION OF STIMULUS AND TREATMENTS Skin conductance Finger pulse volume Treatment
CS response
Conditioning Sensitization CS alone
Pre-US response
Post-US response
Phobic
Neutral
Phobic
Neutral
Phobic
Neutral
Phobic
Neutral
.533 .265 .045
.333 .235 .019
.342 .111
.140 .069 .008
.365 .135 .003
.222 .130 .003
.086 .074
.106 .073 .015
.014
.089
Note. Abbreviations: CS = conditioned stimulus; US = unconditioned stimulus.
Stimulus X Conditioning effects. For the CS response, the significant effect of conditioning was due to larger responses in the conditioning and sensitization groups as compared to the CS-alone groups. The tendency toward better conditioning to phobic stimuli was not significant. For the pre-US response, all 3 effects shown in Table 2 were significant. The interaction between stimulus and conditioning was due to better conditioning to phobic stimuli. Thus, the phobic conditioning groups exceeded both the phobic sensitization and CS-alone groups, which did not differ, whereas there were no significant differences between the neutral groups. Furthermore, the phobic conditioning group showed significantly larger responses than the neutral conditioning group, whereas no difference emerged between the sensitization and CS-alone groups for the 2 types of stimuli. The significant main effect
of conditioning on the post-US response, finally, was due to larger responses in the conditioning than in the sensitization and CS-alone groups. The results for the within-subjects acquisition analyses are shown in Figure 1. The CS responses were larger to phobic than to neutral stimuli, and the conditioning groups tended to exceed the sensitization and CSalone groups in response magnitude. Table 2 shows that the stimulus effect was significant, but the significant conditioning effect pertained to larger responses in the conditioning and sensitization groups as compared with the CS-alone group. In addition, the effect of trials was significant (F — 2.81, df - 4/126, p < .05), as well as the Trials X Conditioning interaction (F — 3.74, df = 8/126, p < .01), the latter being due to the initial rise in the acquisition curves for the conditioning groups as compared with the
TABLE 2 F RATIOS FOB THE STIMULUS, CONDITIONING, AND STIMULUS X CONDITIONING EFFECTS DURING ACQUISITION Between-subjects analysis Source
Skin conductance response df
Stimulus (S) Conditioning (C) S X C
1/108 2/108 2/108
CS
Pre-US
Post-US
2.02 13.52*** .97
6.52* 17.13** 3.40*
1.05 12.04*** .95
Within-subjects analysis Finger pulse volume
df
1.07 2.10 2.57
1/54 2/54 2/54
Skin conductance response CS
Pre-US
4.66* 6.40** .88
2.57 3.61* .53
Note. Abbreviations: CS = conditioned stimulus, US = unconditioned stimulus. * p < .05. ** p < .01. *** p < .001.
Finger pulse volume
3.21 1.10 .10
CONDITIONING TO PHOBIC STIMULI
be seen in Table 2 there were only very weak effects of stimulus pairing, and in no case was there any significant effect.
CS response Phobic
Neutral
0.90
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0,80 0,70
0.60 0.50 0.40 0,30 0,20 ,_ 0.10
1
2
3
4
Conditioning
5
1
2
3
4
5
*—»Sensitization •—• CS alone Pre-UCS response Neutral
Phobic
1
2
3
4
5
Acquisition trials
FIGURE 1. Skin conductance conditioned stimulus (CS) and pre-unconditioned-stimulus (preUCS) response acquisition curves for the phobic and neutral conditioning, sensitization, and CSalone groups (n = 10).
falling or flat functions for the other treatments. The pre-US responses showed tendencies similar to those of the CS response, but as shown in Table 2 only the effects of conditioning were significant. Follow-up tests showed that only the conditioning groups differed from the CS-alone groups. As was the case with the CS response, there was a Trials X Conditioning interaction (F = 5.00, df = 8/216, p < .01), which was due to the increasing trends over trials in the conditioning groups in contrast to the falling trends of the sensitization and CS-alone groups. Finger pulse volume responses. Data from the between-subjects acquisition analysis are shown in Table 1, and those from the within-subjects analysis in Table 3. As can
Extinction Separate analyses of variance with a split plot 5 x 3 x 2 x 2 design were carried out for each response measure during extinction. As before, Tukey tests were used in followups. Skin conductance responses. The mean response magnitudes for the skin conductance measures are shown in Figure 2. Since there were no effects of number of reinforcements, the data were collapsed for this factor. The results were similar for all 3 response components: There was a slow overall decrease with extinction trials, the overall responding tended to be higher to phobic than to neutral stimuli, and whereas there was an immediate and rather abrupt extinction effect in the neutral groups, the phobic conditioning groups continued to respond throughout the extinction period. The relevant statistics are given in Table 4. Follow-up tests showed that the conditioning groups differed from both the sensitization and CS-alone groups in the phobic condition, whereas no significant differences between groups emerged with the neutral stimulus. The effect of the phobic stimulus was a specific associative one, since the phobic conditioning groups exceeded the neutral conditioning groups, whereas the phobic sensitization and CSalone groups did not differ from the neutral sensitization and CS-alone groups. The TABLE 3 MEAN FINGBE PULSE VOLUME RESPONSES (% VOLUME PULSE CHANGE) DUEING ACQUISITION AND EXTINCTION Acquisition
(n = 10)
Treatment
Extinction
(» = 20)
Phobic Neutral Phobic Neutral
Conditioning Sensitization CS alone
.095 .080 .062
.066 .040 .040
.080 .064 .049
.073 .046 .033
Note. Data are collapsed over number of reinforcements. Abbreviation: CS = conditioned stimulus.
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A. OHMAN, A. ERIKSSON, AND C. OLOFSSON CS response Neutral
0,50 0.40 0,30 0,20 0,10
J 1
2
3
4
i Conditioning
5
1
2
*—* Sensitizalion
3
4
5
•—• CS alone
Pre-UCS response Phobic
0,30
Neutral
0,20 0,10
1
2
3
4
1
5
2
3
4
5
Post-UCS response Neutral
Phobic
0,30
0,30
0,20
0,20
0,10
0,10
1
2
3
4
5
1
E x t i n c t i o n trial blocks
FIOUBE 2. Skin conductance conditioned stimulus (CS), pre-unconditioned-stimulus (pre-UCS), and post-UCS response extinction functions for the phobic and neutral conditioning, sensitization, and CS-alone groups. (Data were collapsed for the number of reinforcements factor; n = 20.)
post-US response was the only one to show a genuine extinction effect since, according to the Trial X Conditioning interaction (F = 3.60, df = 8/432, p < .001), the conditioning groups tended to converge with the sensitization and CS-alone groups as a function of extinction trials. Finger pulse volume responses. The means for finger pulse volume responses collapsed over trials and number of reinforcements are shown in Table 3. The response magnitude diminished as a function of trials and there were overall differences between the different modes of stimulus presentation (see Table 4). Follow-up tests showed that the conditioning groups definitely exceeded the CS-alone groups (p < .01), and that they tended to
exceed also the sensitization groups (p < .10). Ratings of discomfort. The subject's ratings of discomfort produced by the type of stimulus he had as CS were summed over the 5 stimuli, and a difference between the ratings before and after the conditioning session was computed. Conditioning, sensitization, and CS alone were compared pairwise with t tests for phobic and neutral stimuli. The groups conditioned to snakes had a significantly higher difference than those conditioned to houses (t = 2.14, df = 18, p < .05), with means of 2.05 and .35, respectively. For sensitization and CS-alone groups there were no significant differences. DISCUSSION The present data show unequivocally that electrodermal responses conditioned to phobic stimuli are much more resistant to extinction than responses conditioned to neutral stimuli. Whereas all response components showed immediate and complete extinction in the latter case, they showed rather complete resistance to extinction in the former. This effect, furthermore, was a specific associative one, since the phobic conditioning groups differed from the phobic sensitization and CS-alone, and from all the neutral, groups. The ineffectiveness of the number-of-reinforcements factor indicates that the responses to phobic stimuli reached full resistance to extinction after TABLE 4 F RATIOS FOR THE TRIALS, STIMULUS, CONDITIONING, AND STIMULUS X CONDITIONING EFFECTS DURING EXTINCTION Skin conductance response [Source
Trials (T) Stimulus (S) Conditioning (C) S XC
df
4/432 1/108 2/108 2/108
CS
Pre-US
8.24*»* 10.06** 15.16*** 4.31*
4.66*** 8.46** 12.72*** 5.06**
PostUS
Finger pulse volume
10.27*** 5.36*** 8.14** 2.24 15.35*** 4.81** 3.91* .13
Note. Abbreviations: CS = conditioned stimulus; US unconditioned stimulus. * v < .05. ** p < .01. *** p < .001.
CONDITIONING TO PHOBIC STIMULI
only one CS-US pairing, whereas for the neutral stimuli there was no resistance to extinction even after 5 CS-US pairings. In conclusion, then, it can be stated that the expectations from prepared learning theory were fully confirmed for the extinction electrodermal data. The electrodermal acquisition data were less consistent. For the CS response, the conditioning and sensitization groups exceeded the CS-alone groups, but did not differ between themselves in either of the 2 analyses; and there was no effect of type of stimulus, although the tendency was in the direction of the hypothesis. The post-US response, too, failed to show superior conditioning to the phobic stimuli, although there were overall effects of conditioning. For the pre-US response, finally, there was a discrepancy between the results from the between- and within-subjects analyses. In the former, there was a significant conditioning effect to the phobic but not to the neutral stimuli, and, as in the case of the extinction data, this effect was specifically associative. In the within-subjects analysis, the tendencies were in the same direction, but only the overall difference between the conditioning and CS-alone groups was significant. Thus, the prepared learning hypothesis was only partially confirmed for the pre-US response and clearly disconfirmed for the CS and post-US responses. The finger pulse volume responses showed no significant effects during acquisition, and during extinction the conditioning groups exceeded only the CS-alone groups. Although it is possible to condition this response system in a single cue paradigm (Ohman, 1974b), very few conditioning trials were used in the present study, which might prevent the possibility of observing a conditioning effect. Furthermore, peripheral vasomotor changes are less sensitive to psychological impact than are electrodermal responses (Furedy & Gagnon, 1969). Therefore, the present negative findings may indicate that vasomotor responses are less sensitive than electrodermal ones, and that the situation was nonoptimal for learning, rather than being a source of evidence against the prepared learning theory.
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The results for the remaining dependent variable, the subjective ratings of discomfort, were positive to the prepared learning hypothesis. Thus, there were differences between the conditioning groups given phobic and neutral stimuli, but not between any other groups. This means that there were detectable subjective effects of the phobic conditioning procedure. Since there was very little extinction of the electrodermal responses to phobic stimuli, but rather complete disappearance of responses to neutral ones, the results from the ratings are in good agreement with those for the autonomic measure. In comparing the present results with those of the previous study (Ohman et al., in press), 3 points appear to be especially relevant. First, the objective of optimalizing the conditions for observing the effects of phobic stimuli obviously was successfully fulfilled. Thus, in the previous data, there were clear-cut effects of the phobic stimulus only on the CS responses during extinction, whereas, in the present instance, the effects were quite clear for all 3 response components during extinction, and, to a lesser extent, for the pre-US response during acquisition. Second, the very rapid extinction to the neutral CSs was of some importance to the success in demonstrating differences between phobic and neutral stimuli in both the previous and the present study. In conventional situations with tone or light CSs, about 10 trials seem to be needed for complete extinction (e.g., Ohman, 1974a; Ohman & Bohlin, 1973), whereas the responses to the supposedly neutral house stimuli disappeared instantly when the US was discontinued. Therefore, it is tempting to speculate that the so-called "neutral stimuli" in effect come from the contraprepared side of the preparedness continuum. These speculations open the possibility of turning the preparedness concept into a true dimension by comparing prepared, unprepared, and contraprepared human autonomic conditioning in the same experimental situation. Third, the conclusion regarding preparedness differed in both studies according to whether it was based on acquisition or ex-
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A. OHMAN, A. ERIKSSON, AND C. OLOFSSON
tinction data. This finding restricts the gen- from which preparedness can be predicted. erality of the preparedness concept (cf. Thus, the preparedness concept is anchored Seligman & Hager, 1972, p. 5) in demon- primarily on the dependent variable side, strating that acquisition and extinction data and from the history of psychology we know are independent, the latter fulfilling the cri- that this might be a paramount problem. terion of prepared learning, whereas the The present results, for instance, may be former does not. taken as support for the proposition that A couple of more general problems with phobias are instances of prepared learning. the preparedness concept are raised by the If they are interpreted as supporting the nopresent project. First, one may not legiti- tion that prepared learning is very slow to mately conclude that our results show that extinguish, however, the circle is completed. phobias are based on an inherited disposiThus, it appears that the theory of pretion to associate fear with certain situations. pared learning is faced with a number of imThis is clearly implied in the theory, but this portant problems. Nevertheless, it has assumption was not tested in either of the pointed out the significance of biological 2 studies, nor can it ever be directly tested context for learning, and it has suggested a in the present context. This is, in fact, a number of significant problems for empirical fundamental weakness in Seligman's theory, analysis. A more careful evaluation of the since, instead of suggesting a "resolution of theory, therefore, must wait for the accumuthe instinct-learning controversy [Seligman lation of further knowledge. & Hager, 1972, p. 1]," the preparedness conREFERENCES cept leaves us with the problem of determining the genetical or experiential basis for the Furedy, J. J. Human orienting reaction as a funcpreparedness. A monkey with a well-learned tion of electrodermal versus plethysmographic response modes and single versus alternating learning set certainly shows "preparedness" stimulus series. Journal of Experimental Psycholwhen faced with a new discrimination probogy, 1968, 77, 70-78. lem, but it is only through knowledge of the Furedy, J. J., & Gagnon, Y. Relationships between background factors that we can explain this and sensitivities of the galvanic skin reflex and behavior in terms of more complex learning two indices of peripheral vasoconstriction in man. Journal of Neurology, Neurosurgery, and Psyrather than in terms of genetical endowment. chiatry, 1969, 32,197-201. For the present data, it remains to be Garcia, J., McGowan, B. K., & Green, K. F. Bioshown that it is the content of the snake piclogical constraints on conditioning. In A. H. tures, as required by the prepared learning Black & W. F. Prokasy (Eds.), Classical conditioning II: Current research and theory. New theory, and not some abstract property such York: Appleton-Century-Crofts, 1972. as attensity, novelty, or complexity, that is W. W., & Lockhart, R. A. Effects of "anxieffective in producing the superior resistance Grings, ety-lessening" instructions and differential set deto extinction. A plausible line of reasoning is velopment on the extinction of GSR. Journal of to argue that the snake pictures for such Experimental Psychology, 1963, 66, 292-299. reasons (but cf. Klimova, 1965) provoke Hagfors, C. The galvanic skin response and its application to the group registration of psychomore orienting responding which in turn physiological processes. (Jyvaskyla Studies in gives better conditioning (cf. Ohman & Education, Psychology, and Social Research, No. Bohlin, 1973), and in this case there is no 23) Jyvaskyla, Finland: University of Jyvaskyla, need to invoke genetical-evolutionary con1970. cepts in the explanation. Such an argument Klimova, V. I. The character of the components of some orientational reactions. In L. G. Voronin, is strengthened by the observation of larger A. N. Leontiev, A. R. Luria, E. N. Sokolov, & orienting responses to phobic than to neutral O. S. Vinogradova (Eds.), Orienting reflex and stimuli during the initial habituation trials. exploratory behavior. Washington, D.C.: American Institute of Biological Sciences, 1965. A second problem with the preparedness concept is that it runs the danger of becom- Lockhart, R. A. Comments regarding multiple response phenomena in long interstimulus interval ing circular. This is so since evolution is conditioning. Psycho-physiology, 1966, 3, 108-114. open to speculative interpretations, rather Ohman, A. Orienting reactions, expectancy learnthan presenting a well-established theory ing, and conditioned responses in electrodermal
CONDITIONING TO PHOBIC STIMULI conditioning with different interstimulus inter.. vals. Biological Psychology, 1974, 1,189-200. (a) Ohman, A. The relationship between electrodermal and digital vasomotor responses in aversive classical conditioning. Biological Psychology, ..1974,2,17-31. (b) Ohman, A., & Bohlin, G. Magnitude and habituation of the orienting reaction as predictors of discriminative electrodermal conditioning. Journal of Experimental Research in Personality, 1973, 6, 293-299. Ohman, A., Erixon, G., & Lofberg, I. Phobias and preparedness: Phobic versus neutral pictures as conditioned stimuli for human autonomic re-
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sponses. Journal of Abnormal Psychology, in press. Rozin, P., & Kalat, J. Specific hungers and poison avoidance as adaptive specialization of learning. Psychological Review, 1971, 78, 459-486. Seligman, M. E. P. On the generality of the laws of learning. Psychological Review, 1970, 77, 406418. Seligman, M. E. P. Phobias and preparedness. Behavior Therapy, 1971, 2, 307-321. Seligman, M. E. P., & Hager, J. E. (Eds.) Biological boundaries of learning. New York: AppletonCentury-Crofts, 1972. (Received November 30, 1973)
