The effects of compound in vivo and imaginal exposure: A test of fear enhancement models

BEHAVIOR THERAPY 14, 345--356 (1983)

The Effects of Compound In Vivo and Imaginal Exposure: A Test of Fear Enhancement Models

DANNY G. KALOUPEK

Concordia University

Eysenck has hypothesized that extinction procedures, such as those used in flooding and implosive therapy, contain implicit aversive reinforcement contin- gencies which may increase conditioned fear. An alternative view has been proposed by Gordon and his colleagues, who suggest that memory reactivation is responsible for instances of increased fear responding. The present study was designed as a differential test of these proposals. Female students who demonstrated avoidance of a harmless snake were presented with in vivo exposure to the snake in an attempt to replicate previous demonstrations of fear enhancement. Imaginal exposure was added for half of the groups. The primary findings were: (l) a generally linear relationship between the total amount of exposure (whether in vivo and/or imaginal) and improvement in both behavioral approach to the fear stimulus and self-reports of fear; (2) greater physiological improvement associated with combined in vivo and imaginal exposure. Fear enhancement was not repli- cated and the results were not consistent with Eysenck's incubation model. In- stead, the findings support two-factor avoidance theory and are compatible with Gordon's proposal. Additionally, a question is raised regarding the suitability of control procedures in existing between-groups demonstrations of fear enhancement.

T h e i nc rea sed use o f e x t i n c t i o n - b a s e d t e chn iques such as f looding and i m p l o s i v e the rapy has f ocused a t t en t ion on the t heo re t i ca l founda t ion o f these p r o c e d u r e s . O n e of the m o s t p r o m i n e n t c o n t r o v e r s i e s to e m e r g e in this a r ea c o n c e r n s the abi l i ty o f n o n r e i n f o r c e d CS e x p o s u r e to e n h a n c e the s t rength o f ( cond i t ioned) fear r e spond ing . T h e main p r o p o n e n t o f the fea r e n h a n c e m e n t h y p o t h e s i s is E y s e n c k (1968, 1976, 1979), w h o has l abe led the e f fec t " i n c u b a t i o n . " T h e o r e t i c a l l y , i ncuba t ion cha l lenges the

This paper is based upon a doctoral dissertation submitted to the State University of New York at Binghamton. Portions of the study were presented at the annual convention of the Association for Advancement of Behavior Therapy, New York, 1980. Special ap- preciation is extended to Donald J. Levis for his able supervision of this research. The helpful suggestions of Francis J. Keefe regarding manuscript revision are also gratefully acknowledged. Reprint requests should be sent to Danny Kaloupek, Department of Psy- chology, Concordia University, 1455 deMaisonneuve W., Montreal, Quebec, H3G 1M8, Canada.

345 0005-7894/83/0345-035651.00/0 Copyright 1983 by Association for Advancement of Behavior Therapy

All rights of reproduction in any form reserved.

346 KALOUPEK

classical view that the sole enduring result of nonreinforced exposure is a reduction in conditioned responding. Practically, it raises questions concerning the safety of flooding procedures since, conceivably, patients might be made worse by such treatment.

Eysenck's (1979) model for incubation emphasizes the role of CS-pro- duced conditioning factors. This model maintains that the conditioned fear response has an unconditioned aversive stimulus component that enhances fear responding. According to Eysenck, the duration of CS exposure and the strength of the conditioned fear response are important considerations. Duration below a critical threshold and response strength above a critical threshold are both required for response enhancement to occur. If either factor is absent, extinction will be stronger than incubation and the CR reflecting fear will decrease--as predicted by classical theory. The most direct support for this type of incubation effect comes from studies which demonstrate within-subject increases in fear responding due to CS-only presentation (e.g., Campbell, Sanderson, & Laverty, 1964; Dykman, Mack, & Ackerman, 1965; Napalkov, 1963).

Gordon, Smith, and Katz (1979) have proposed an alternative to Eysenck's model. According to Gordon, CS exposure may produce cuing or reactivation of memories concerned with original learning. This reactivation creates a compound CS by generating cognitive stimuli which combine with the nominal fear stimulus. The development of the compound fear stimulus is responsible for enhanced response strength. Fur- thermore, reactivation is assumed to occur with a shorter latency than does extinction. Thus, CS exposure which is too brief may produce response enhancement because reactivation operates in the absence of extinction effects.

Studies of fear enhancement based on between-groups comparisons (e.g., Miller & Levis, 1971; Rohrbaugh & Riccio, 1970; Stone & Borko- vec, 1975) have not demonstrated increases in fear responding; even short duration exposure has reduced fear responding. However, these studies indicate that no-exposure control groups sometimes show reductions in fear responding that are superior to short exposure groups. At present, this outcome is consistent with both incubation and reactivation models.

The present study tested differential implications of the incubation and reactivation models within the context of between-groups demonstrations of the fear enhancement effect. Three durations (0, 15, and 60 min) of in vivo exposure to a fear-eliciting stimulus (snake) were delivered to in- dependent groups of subjects. It was expected that the posttest improvement (fear reduction) shown by the 60 min exposure group would be the greatest, followed by the 0 min group, followed by the 15 min group (see Miller & Levis, 1971; Stone & Borkovec, 1975). In addition, a comparable set of three groups was administered a 15 min description of the snake, much like the type of imaginal scene that might be presented in implosive therapy (Levis & Hare, 1977, Cue categories 1 & 2). The imagery tape was presented in conjunction with on-going in vivo exposure in order to create a compound fear stimulus.

F E A R E N H A N C E M E N T M O D E L S 347

The outcome for the two 15 min in vivo exposure groups was the basis for differentiating the theoretical positions. According to Eysenck's (1979) model, the addition of the imaginal cues would be expected to produce fear enhancement beyond that shown by in vivo exposure alone. In con- trast, the reactivation model of Gordon et al. (1979) predicts greater extinction as the result of the addition of imaginal cues. The basis for this prediction is the assumption that imaginal cues can facilitate memory reactivation, thereby allowing more of the exposure time to be function- ally devoted to extinction.

METHOD Subjects

The subjects were sixty female undergraduate students who scored 5 or more on item 39 ("Snakes") of the Fear Survey Schedule II (Geer, 1965) and who also failed to touch a harmless laboratory snake (3 ft. boa constrictor) at the end of a behavioral approach pretest.

Apparatus The reader is referred to the study by Kaloupek, Peterson, Boyd, and

Levis (1981) for details concerning the experimental room and equipment. The only differences were: (1) a finger temperature measure which was recorded by way of a bead thermistor affixed to the middle finger of the nondominant hand (see Boudewyns, 1976), and (2) psychophysiological data were scored by an Interdata (Model 70) mini-computer.

Design The study was a 3 z 2 factorial design (n = 10) with in vivo exposure

duration (duration) and imagery tape presentation (imagery) as the two factors. The three exposure durations were 0, 15, and 60 min. The 15 min imagery tape was either present or absent. A blocking procedure based on the number of steps completed during the behavioral approach pretest was used to insure the equalization of assignment to groups in terms of initial fear behavior.

Procedure Pretest. Testing of initial fear response began with a 10 min baseline.

This was followed by a passive minute viewing period and a behavioral approach test which were identical to the procedures described by Kal- oupek et al. (1981).

Exposure period. A 5 min baseline period began the exposure period. All subjects were then told to observe either the snake or the empty Plexiglas box (depending on group assignment) located at the end of the runway nearest them. At the end of this 45 min exposure period, the curtain was closed in order to screen subjects from the test apparatus. Then, the box was moved to the far end of the runway, the snake was supplied (if necessary), and the box was returned to the point nearest the subject.

348 KALOUPEK

The tape-recorded imagery scene was delivered (if appropriate) when the curtain reopened. The scene, which described the snake escaping from the Plexiglas box, was 5 rain in duration and was repeated three times. Subjects were instructed to keep their eyes open while imagining the scene.

Posttest. The final test sequence was identical to the pretest except that the length of the baseline was 5 min. A stimulus attributes checklist was administered following the test as a means of quantifying the sub- jective stimulus conditions experienced by the participants. This measure was comprised of a list of both positive and negative adjectives and brief descriptive phrases which subjects in previous studies had applied to the snake. Subjects checked those attributes which they had thought about or noticed during the experiment.

Dependent Measures

Behavioral approach measures. The latency for each approach test button press was recorded directly in tenths of seconds from an electronic timer. The mean of the (variable number of) completed button press latencies and the final recorded latency (irrespective of the number of button presses completed) were used as indices of approach behavior. The number of completed button presses and a dichotomous measure of whether or not subjects were able to touch the snake were also recorded by the experimenter.

Self-report measures. The Fear Thermometer (Walk, 1956) and Affect Adjective Checklist (Zuckerman, 1960) were administered following minute view and approach test phases (see Kaloupek et al., 198 l) during both the pretest and posttest. The stimulus attributes checklist was administered at the completion of the experiment.

Psychophysiological measures. The number of heart beats recorded during a 1 min period was used as the heart rate (HR) index. Two parameters of the skin conductance measure were scored. Level (SCL) was the average of six minimum conductance values, each derived from consec- utive 10 sec segments of the 1 rain period in question. The number of responses (SCR) exceeding 0.2 micromhos in each minute period was the second index.a Finger temperature (TEMP) was scored as the average of the six values representing the highest temperature in each of the con- secutive l0 sec intervals in a minute period.

RESULTS No-Touch vs. Touch Subjects

The pretest measures were compared by way of an analysis of variance for the 60 subjects who failed to touch the snake and the 16 subjects who did touch the snake and were eliminated. Each of the behavioral and self-

1 The SCL/SCR data for one subject in the 0 min in vivo and imaginal exposure group was lost due to equipment malfunction.

FEAR ENHANCEMENT MODELS 349

report measures except final latency (p < .06) indicated significantly greater fear for the no-touch group. Similar analysis conducted on the psychophysiological measures, however, revealed neither absolute nor change score differences between no-touch and touch subjects.

Outcome Measures

Changes in responding from pretest to posttest were assessed by way of a 3 × 2 (duration × imagery) analysis of covariance. Posttest measures were analyzed with the pretest scores from each measure as the covariate. The assumptions of linearity and homogeneity of regression (cf. Keppel, 1973) were tested for each analysis along with a 3 × 2 analysis of variance to determine whether chance differences existed during pretesting.

Behavioral approach measures. The analysis for the mean latency measure revealed a significant main effect for duration, F(2,53) = 5.04, p < .01. Follow-up comparisons using the common MS error term revealed that both level 15 min and level 60 min differed significantly from level 0 min (p < .05). The former two exposure levels did not differ from each other. The adjusted main effect means for levels 0, 15, and 60 min were 6.1, 2.1, and 3.0 sec, respectively. The analysis for the final latency measure revealed a similar outcome.

A trend analysis was also conducted across exposure groups in order to explore the relationship between the exposure variable and changes in behavioral latency measures (cf. Shipley, 1974). The six groups were ordered in terms of the total amount of exposure (both in vivo and imaginal) and the trend components were determined across these six points. 2 Mean latency and final latency scores were both characterized by significant linear (p < .03) and quadratic (p < .05) trends. The adjusted group means for the mean latency scores are presented in Fig. 1. Examination of the figure reveals a general pattern of decreasing latencies associated with increasing total exposure. A deviation from the linear decline occurs between the 15 min compound in vivo and imaginal exposure group and the 60 min in vivo alone group.

Posttest measures of the button press frequency and physical contact with the snake were analyzed by a complex chi square test (Bruning & Kintz, 1977). No significant effects emerged from either analysis.

Self-report measures. Covariance analysis of the Fear Thermometers and the Affect Adjective Checklists revealed no significant differences. This outcome led to a more detailed examination of the self-report data for individual subjects. One difficulty which became evident was that two subjects in each group recorded higher posttest self-report scores associated with greater approach behavior during the approach test. Appar- ently, changes in fear stimulus proximity from pretest to posttest altered

2 Technically, the use of trend analysis can be questioned because of the inability to meet the assumption of equal intervals across the total exposure variable. However, the clarity afforded by this type of analysis was considered sufficient justification for its use.

350 KALOUPEK

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the functional intensity of the fear stimulus (Kaloupek et al., 1981) and thereby reduced the comparabili ty of the conditions under which the self- report measures were administered.

The two subjects in each group with increased scores were dropped from consideration in order to reduce the impact of variable distance on the two approach test self-report measures. The change scores were then subjected to a trend analysis as had been applied to the behavioral latency data. The group change score means for the Affect Adjective Checklist are displayed in Fig. 2. As the figure suggests, the analysis revealed only a significant linear trend, F(1,42) = 4.35, p < .05, with greater exposure associated with greater reductions in self-reports of fear. A similar pattern was shown by the Fear Thermometer change scores, although the linear effect did not reach statistical significance.

A final 3 x 2 analysis of variance was applied to the stimulus attributes checklist scores, and no significant differences were found for any effect.

Psychophysiological measures. The three periods of 1 min duration which were examined for each psychophysiological index were: (1) the last minute of the baseline period; (2) the minute view period; (3) the final minute of the instructions for the approach test. The latter period was selected instead of a period during the approach phase of the test due to movement artifacts and variable time factors associated with the test procedure.

The analysis of covariance applied to the HR scores revealed significant


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FIG. 2. Mean change from pretest to posttest for Affect Adjective Checklist scores based on a restricted number of subjects (n = 8). Groups are ordered from least to most total exposure (tape = imaginal exposure).

duration main effects at each of the three periods, all F's(2,53)/> 3.80, p < .05. Specific main effect comparisons revealed that the combined 60 min exposure groups had the highest heart rate during each period. For example, even at the end of the baseline the respective adjusted HR means for levels 0, 15, and 60 min were 76.3, 75.2, and 80.3 beats/min.

No significant differences were revealed in the overall covariance analysis of either the SCL or SCR measures.

The results for the covariance analysis of the TEMP measures were uniform in indicating a main effect for imagery during each of the three periods, all F's(1,53) /> 6.18, p < .03. The subjects who were administered the imagery tape clearly showed lower finger temperatures throughout the test procedure. Again, even at the end of the baseline, the adjusted means for combined no-imagery vs. imagery groups were 27.8 vs. 26.1 degrees C.

Examination of individual subject data suggested that individual differences in responsivity across physiological channels were masking treatment-related effects. A more individually based analysis was, therefore, conducted in order to address this difficulty. Difference scores were calculated to reflect responding during the minute view and approach test instructions relative to the end of baseline, and each subject was labeled as a responder or non-responder in terms of each of the four indices. The

352 KALOUPEK

responsivity criteria for HR, SCL, SCR, and TEMP, respectively, were pretest changes from baseline greater than or equal to +6 beats/min, + 1.6 micromhos, +4 SCR's, and -1 degree C. Then pretest responding and posttest responding were compared for matching intervals for each measure on which a subject was classified as a responder. The comparison was recorded as improved if there was less responding during the posttest?

An index of general improvement was recorded if the majority of individual response measures were improved (e.g., 2 out of 3 measures for which a subject was classified as responsive). This general index revealed significant differences limited to the imagery factor. During the minute view period the percentages of improved subjects in no-imagery (48%) and imagery (78%) conditions differed significantly (z = 2.14, p < .03). A similar outcome was also evident during the approach test instruction period (z = 2.15, p < .03), although the overall improvement rates for both conditions were somewhat higher (no-imagery = 71%; imagery = 93%).

Exposure (Process) Measures An analytic approach similar to that used with outcome measures was

followed for the psychophysiological measures monitored during the exposure period. The final step in the overall plan was a repeated measures analysis of covariance, for which the total exposure period was divided into two segments.

The early exposure segment was comprised of measurements at minutes 1, 15, 30, and 45 of exposure. Therefore a 3 x 2 × 4 (duration x imagery × phase) analysis of covariance was conducted, with the final baseline minute as the covariate. The emphasis of this analysis was on the potential differences between the 60 min exposure groups and each of the other two exposure durations, since only the 60 min groups received in vivo exposure through the first 45 min of the manipulation. Late exposure was comprised of minutes 46, 51, and 56 of the procedure. These points correspond to the 1st, 6th, and 1 lth min of the tape presentation (if it was delivered). A 3 × 2 x 3 (duration × imagery × phase) analysis of covariance was applied, again using the final baseline minute as the covariate. This analysis was intended to examine possible differences associated with the imaginal exposure manipulation.

3 As a preliminary test of the appropriateness of the responsivity criteria, the no-touch subjects were compared with touch subjects to determine whether the percentage of responders for each measure differed on the basis of fear levels. Ideally the responsivity classification would not be fear-related because the nature of the individual differences in question are assumed to be primarily based on physiological characteristics. In fact, tests of differences between proportions revealed no differences between no-touch and touch groups (approximate percentages of responders: HR = 64%; SCL = 71%; SCR = 66%; TEMP = 38%).


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FIG. 3. Heart rate and skin conductance response measures during late exposure minutes. Plotted values represent adjusted means for the imagery (tape) × phase interaction derived from analysis of covariance.

Early exposure. The within-subject phase effect across early exposure periods was significant for HR, SCL, and TEMP (p < .01). In general, these phase effects were associated with elevated responding during the beginning of the segment and recovery at the end. No significant effects emerged for duration or imagery factors.

Late exposure. Significant phase effects were also found during late exposure for SCL, SCR, and TEMP (p < .01). More importantly, the imagery x phase interaction was significant for HR, F(2,108) = 5.09, p < .01; SCR, F(2,106) = 3.19, p < .05; and TEMP, F(2,108) = 3.33, p < .05. The adjusted means reflecting this interaction for HR and SCR are presented in Fig. 3. Both measures can be seen to have higher values across the three phases for subjects who were presented the tape-recorded imagery scene. Only the last two data points, however, appear to differentiate main effect imagery groups on HR, while only the first and third points appear to differentiate the groups on SCR. These impressions were confirmed by specific comparisons (all p ' s < .05).

The subjects who received the imagery scene had lower TEMP scores throughout late exposure. Specific comparisons confirmed that the differences between imagery main effect groups were significant at each of the three points (all p 's < .03). The imagery x phase interactions for TEMP during late exposure appeared to be attributable to decreases shown by subjects who were exposed to the tape-recorded scene. Comparisons between phases revealed that subjects exposed to the imagery tape de- creased significantly between min 46 and min 51 (p < .01) and between min 51 and min 56 (p < .05). The no-imagery subjects did not show significant changes across either interval.

354 KALOUPEK

DISCUSSION The primary findings relating to outcome measures were: (1) longer

approach latency for the combined 0 rain exposure groups relative to the 15 rain and 60 rain exposure groups; (2) linear relationships between total exposure and reductions in both approach latency and self-report measures of fear; and (3) greater improvement on psychophysiological measures for subjects who received the combined in vivo and imaginal exposure. The latter finding was accompanied by psychophysiological process results which indicated that the combined exposure condition generated greater arousal (HR and SCR increase; TEMP decrease) during the late exposure period.

The results of the present study failed to show the anticipated response enhancement effect. Contrary to previous findings (e.g., Miller & Levis, 1971; Stone & Borkovec, 1975), there were no instances where the no- exposure group improved more than either of the 15 min exposure groups.

The lack of response enhancement is problematic in terms of initial predictio~as, although it is still possible to address some differential implications of the Eysenck (1979) and Gordon et al. (1979) models. In particular, the beneficial effect of greater exposure on approach latency and self-report measures is consistent with Gordon's model if it is assumed that reactivation of memories occurred rapidly so that extinction could begin, Under such circumstances, this model makes predictions similar to two-factor avoidance theory (cf. Levis & Hare, 1977; Shipley, 1974). Both predict a direct relationship between amount of exposure and magnitude of fear reduction. Eysenck's incubation model, however, predicts less extinction if exposure intensity is increased (as with compound in vivo and imaginal exposure) while exposure duration is held constant. The present findings contradict this implication of the incubation model.

Comparison with the studies of Miller and Levis (1971) and Stone and Borkovec (1975) suggests a procedural factor which may have been in- strumental in the present failure to find response enhancement. In the previous studies no-treatment subjects were removed from stimuli associated with testing and exposure by having them engage in extraneous activities (e.g., reading) during the exposure period. The present no-treatment subjects were exposed to all of the stimulus conditions except the presentation of the nominal fear stimulus. Exposure to these contextual cues may have generated reactivation effects (i.e., response enhancement) which were not countered by extinction effects. The possibility of memory reactivation would also explain why subjects who were not exposed to the snake had stimulus attributes checklist scores and psychophysiological response values during early exposure which were equal to those for subjects who were exposed to the snake,

A related possibility is that a temporary response reduction similar to the Kamin effect (Kamin, 1957) was initiated by the pretest procedure. Nonreinforced CS exposure may have reactivated fear-related memories and disrupted this effect. On the basis of this argument, previous control

FEAR ENHANCEMENT MODELS 355

procedures may be viewed as inadequate since comparisons would be confounded by the operation of the Kamin effect only in the control group. It might, therefore, have been mistakenly concluded that exposure had detrimental effects when, in fact, the absence of exposure simply allowed temporary response reductions for control subjects.

Higher posttest HR for 60 min exposure subjects was an unexpected finding. However, it should be noted that there was a tendency for these subjects to have higher HR scores during late exposure and for subjects in imagery groups to show carry-over of TEMP responding from late exposure to the posttest. This suggests that the final baseline was too short to allow physiological recovery from the demands of exposure. Future investigators may thus find longer baseline periods more suitable.

Finally, two limitations of the present investigation should be noted. First, Eysenck's (1979) formulation is probably best evaluated on the basis of within-subject evidence. Therefore, despite the present findings, the incubation model retains credibility. The outcome of this study does, however, serve to qualify the type of evidence which can be claimed as support for the incubation model, and it calls into question the generality of the response enhancement effect.

Second, the subjects in the present study were probably in the mild- to-moderate range of fear strength. This limitation is not particularly problematic given the similarity of these individuals to subjects in prior studies which prompted the investigation. It should be clear, however, that neither the external validity of the fear assessment nor the clinical generalizability of the findings can be readily determined from the avail- able data.

In summary, the present study demonstrated a relatively linear relationship between amount of nonreinforced exposure to a fear stimulus and decreases in fear responding. This result is more consistent with Gordon's reactivation hypothesis (which has common elements with two- factor theory) than with Eysenck's incubation model of response enhancement. Furthermore, compound in vivo and imaginal exposure pro- duced greater improvement in psychophysiological outcome measures. This set of findings is consistent with the assumptions of flooding and implosive therapy (e.g., Levis, 1980) regarding the value of relatively high-intensity exposure for fear reduction. Finally, the results raise questions regarding previous between-groups evidence for enhancement of fear. It is conceivable that earlier findings reflect control group aberra- tions rather than a direct negative effect of nonreinforced exposure. Fur- ther research is needed to specifically address this issue.

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Dykman, R., Mack, R., & Ackerman, P. The evaluation of autonomic and motor components of nonavoidance conditioned response in the dog. Psychophysiology, 1965, 1, 20%230.

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RECEIVED: July 22, 1981 FINAL ACCEPTANCE: January 28, 1983

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The effects of compound in vivo and imaginal exposure: A test of fear enhancement models