Effects of varied-stimulus exposure training on fear reduction and return of fear

BEHAVIOUR RESEARCH AND THERAPY

PERGAMON

Behaviour Research and Therapy 36 (1998) 719±734

E€ects of varied-stimulus exposure training on fear reduction and return of fear Melissa K. Rowe*, Michelle G. Craske Department of Psychology, University of California, Los Angeles, 1282A Franz Hall, 405 Hilgard Avenue, Los Angeles, CA 90024-1563, U.S.A. Received 1 September 1997

Abstract The current investigation assessed the relative treatment bene®ts of persistence with one speci®c stimulus vs exposure to multiple versions of a stimulus. The study was a 2 (type of stimulus)  3 (assessment occasion) design, in which two spider-fearful groups (N = 28) were compared across three di€erent occasions: pre-treatment, post-treatment, and follow-up. Exposure trials were conducted with the same tarantula for participants in the control group, whereas experimental participants were exposed to four novel tarantulas. As predicted, the control group demonstrated signi®cantly more habituation than the experimental group across exposure trials, yet showed a clear return of fear in response to a control spider at a 3-week follow-up assessment whereas the experimental group showed no increase in fear. These ®ndings o€er support for the bene®cial e€ects of varying the stimulus during exposure, and challenge the reliance on indices of fear activation and habituation as accurate signals of the permanence of fear reduction. # 1998 Elsevier Science Ltd. All rights reserved

1. Introduction In 1979, Rachman coined the term ``return of fear'' (ROF) to describe a phenomenon in which a previously weakened or extinguished fear response appears to recover. Since then, several investigators have attempted to identify the variables which either facilitate or inhibit ROF following fear-reduction. In a review of these e€orts, Rachman (1989) attempted to provide structure and direction to classifying potentially in¯uential variables according to when these determining variables occur. Speci®cally Rachman (1989, p. 165) states, ``Facilitators and inhibitors can operate at all three stages of the return of fear process: pre-training, training, and *Author for correspondence. 0005-7967/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 5 - 7 9 6 7 ( 9 7 ) 1 0 0 1 7 - 1

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post-training''. Although earlier work was focused on identifying variables that promote ROF such as desynchronous fear reduction and elevated heart rate (e.g. Grey et al., 1979; Grey et al., 1981), more recently the focus has shifted to variables that block ROF such as overlearning and post-training practice (e.g. Craske and Rachman, 1987; Phillips, 1985). A recent cognitive model of memory speci®es critical learning variables that may in¯uence fear reduction, and ultimately predict ROF. Bjork and Bjork's (1990) New Theory of Disuse conceptualizes any memory structure as having both storage strength and retrieval strength. Storage strength re¯ects how well a piece of information has been learned; retrieval strength re¯ects the current accessibility of that information. Whereas storage strength of an item is theoretically limitless in its capacity and is always stable or growing in strength, retrieval strength has limited capacity and is subject to a decay in strength. This model can be applied to fear reduction. With only intermittent encounters with targeted feared situations following successful treatment, non-fearful and old, fearful responses to the stimulus (cue) fall into relative disuse. When the stimulus arises again, the relative retrieval strength of the new and old responses will have altered since the end of treatment to be much closer in strength. This regression of memory is attributed to the relative storage strengths of the old and new information. The older memories will not have lost as much retrieval strength over time as the newer memories because the former will likely have much higher storage strength. This would result in an increased probability that the older information in the fear structure would be retrieved when faced with the phobic stimulus after lengthy intervals without stimulus exposure. A period of disuse of both old and new learning followed by recovery of old learning directly parallels Rachman's description of ROF. In a review of the cognitive and motor learning literature, Schmidt and Bjork (1992) were able to distill factors that promote long-term retention following a period of disuse. Three critical variables identi®ed include spaced, random, and variable practices during training. Although these factors may appear to retard learning during the acquisition phase they actually function to enhance long-term retention. Conversely, factors operating during training that enhance immediate performance (e.g. massed, consistent, predictable practices) may ultimately result in deteriorated post-training performance when these factors are no longer present. Schmidt and Bjork (1992) argue that a fundamental error is to focus on performance in the acquisition phase as an indicator of post-training performance. In the context of exposure therapy, massed, repetitious, and predictable sessions may aid in short-term learning, but limit long-term retention and future transfer of learning. ROF following fear-reduction training can be conceptualized as indicative of failed long-term retention and/or failed transfer of learning in response to other situations or stimuli. In support of this conceptualization, Rachman (1989, p. 157) has described ROF as resulting from `` . . . some form of disturbance in consolidation, or dishabituation, or both'', during the period following treatment. Of the variables identi®ed by Schmidt and Bjork (1992), the relative e€ects of spaced vs massed exposure trials has been the most researched in the area of fear reduction. The results of this research are mixed. Two studies found greater reductions in avoidance behavior for massed procedures (e.g. Dua, 1972; Foa, et al., 1988), but greater reductions in self-reported fear (Dua, 1972) and more synchronous reductions in fear (Foa et al., 1988) for spaced procedures. Two other investigations found no relative bene®ts for either massed or spaced

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procedures (e.g. Grey et al., 1981; Chambless, 1990). Schmidt and Bjork (1992) suggested that expanding retrieval practice is the optimal learning schedule for long-term retention. The impact of increasingly expanding intervals between sessions has not yet been investigated with respect to fear reduction. Similarly, the impact of variability and randomness during training on ROF have not been investigated to date. These factors seem closely related to research conducted in the non-primate learning ®eld where variations of context have been shown to impact fear recovery. Speci®cally, the concept of renewal from the animal learning literature o€ers an obvious parallel to fear reduction in humans and ROF following treatment (Bouton, 1988). The basic experimental paradigm as studied in rats involves fear conditioning in Context A, extinction in Context B, and retest in context A, a new context, Context C, or the extinction context B (Bouton and Swartzentruber, 1991). A return to the original conditioning context (Context A), or a shift to a new context (Context C), often produces a renewal of fear (reviewed by Bouton, 1988). It seems the animal learns a contingency that the CS is safe if it occurs in the extinction context. However, in contrast to fear acquisition, extinction is not highly generalizable to other contexts. Thus, learning that a previously feared stimulus is safe in the treatment context may not generalize to occasions when the stimulus is naturalistically encountered following treatment, thus producing ROF. In other words, post-extinction behavior fundamentally depends on the current context and the organism's knowledge of that context because the context disambiguates the meaning of the stimulus (Bouton and Swartzentruber, 1991). In discussing sources of relapse in exposure treatments in humans, Bouton and Swartzentruber (1991) encourage an expanded notion of context in therapy, broadly including any background event or stimulus in which target learning and memory events are embedded (e.g. location, time, stimulus features). Utilizing this de®nition, the stimulus itself can be conceptualized as a contextual retrieval cue. This implies that when the stimulus itself changes, retrieval of original fearful learning may occur. For example, although an individual may learn to be less afraid of a dog throughout treatment, if a di€erent species of dog is encountered post-treatment, retrieval of the original fear response may occur. Therefore, including multiple contexts and stimuli in the extinction process should reduce the rate of fear renewal and relapse, and is analogous to providing variability during training. Based on ®ndings in cognitive and motor (e.g. Schmidt and Bjork, 1992), and non-primate learning (e.g. Bouton and Swartzentruber, 1991), the aim of the current study was to explore the e€ects of varying a stimulus on the process of fear reduction in a spider-fearful sample. It was hypothesized that although providing a series of novel stimuli during exposure practices would create a greater amount of dishabituation, less ROF would result after a 3-week delay. This e€ect parallels Schmidt and Bjork's (1992) observation that sometimes variables that retard learning during training, aid long-term retention. Notably, this is in direct contradiction to predictions of the Emotional Processing theory of fear reduction (Foa and Kozak, 1986) which predicts that dishabituation between exposure sessions leads to less emotional processing and increased ROF. The current study also incorporates three methodological additions not routinely used in ROF research. First, a generalization test at post-training and follow-up assessments was included to measure generalization of fear reduction and to test the role of novel stimuli in generating ROF. Second, dimensional measures of self-reported fear, physiology, and behavior

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were used to examine ROF. Previous research has de®ned ROF arbitrarily as a 10-point increase on a self-report scale of 0±100 (Rachman, 1989). Third, a series of questions at post and follow-up assessments were administered to measure participants' metacognition of fear response during the study. Bjork (1994) proposes that subjective perceptions of training strongly in¯uence the continued use of non-optimal training, in that individuals often prefer the learning method that leads to quick gains, though these gains are often not lasting. Similarly, participants may experience rapid decreases in fear as indicative of more e€ective treatment, although this may ultimately lead to greater ROF. Speci®cally, it was hypothesized that spider fearful participants in a variable stimulus (VS) condition would evidence less fear reduction across a series of four exposure trials as demonstrated on self-report ratings of distress and physiological indices compared to participants in a constant stimulus (CS) condition. During post-training assessments, it was hypothesized that participants in the CS condition would respond less fearfully to a control spider (a spider seen by both groups at pre-training assessment) but more fearfully to a novel spider compared to VS participants. Finally, it was predicted that participants in the CS condition would demonstrate signi®cantly more ROF at a 3-week follow-up assessment compared to participants in the VS condition in response to both a control spider and a novel spider, demonstrating better long-term retention and transfer of learning.

2. Method 2.1. Participants Participants were 28 undergraduate students at the University of California, Los Angeles (8 males, 20 females). Of an original group of 33 participants, two from each condition were excluded due to failure to meet pre-training criteria. One participant from the experimental condition was excluded for failure to complete the experiment. A general measure of fears and phobias was distributed at a mass screening. Participants who scored between 5 and 8 (strongly to extremely anxious) in response to a question about how anxious they would feel touching a spider in a glass cage with a pencil, and a 7 or 8 (de®nitely avoid) on whether they would avoid removing a spider from their bed, were o€ered three units of credit for study participation. Participants were further screened using a Behavioral Assessment Test (BAT). Participants who reported a fear level of at least a 5 or higher (on a 0±8 point scale) during the pretreatment BAT continued in the investigation. 2.2. Experimenters Experimenters included ®ve advanced undergraduate students (3 males, 2 females) majoring in psychology. Experimenters were rigorously trained in the care and handling of tarantulas via several handling practice sessions conducted by the primary investigator and supplementary materials including two books on spiders and an educational video tape. Following this training, experimenters were further trained in the experimental protocol, but were not informed of the hypotheses of the investigation until completion of data collection.

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2.3. Design The study was a 2 (number of stimuli presented during exposure)  3 (assessment time) design, in which two independent groups were compared across three di€erent occasions: pretraining, post-training, and 3-week follow-up. Participants were randomly assigned to either treatment condition, but counterbalanced for gender (4 males and 10 females per group). The two groups refer to two di€erent training conditions: constant-stimulus exposure (CS) vs varied-stimulus exposure (VS). Assessments consisted of BATs, heart rate, and several self-report measures. At pre-training assessment, a BAT was conducted with a spider referred to as the control spider. This spider was presented again at post-training and follow-up assessments. Additionally, a novel spider was used at the post-training and follow-up BATs to test for generalization of fear. A total of seven di€erent tarantulas were used, varying on a variety of dimensions including shape, color, hairiness, quickness, and size (ranging from approximately 1 to 4 in. in abdomen length). Tarantulas were counterbalanced across both conditions so that each spider was represented an equal number of times in each of seven possible presentations. The presentations were: control spider (presented at pre, post, and follow-up), a novel spider at post, a novel spider at follow-up, and a spider for each of the four exposure trials. In order to examine between-S di€erences, each CS participant was yoked to a VS participant and each pair was tested with the same set of spiders in the same order at pre-training, post-training, and followup. Order of presentation of the control and novel spiders at post-training and follow-up BATs was also counterbalanced within groups. During exposure trials, participants in the VS condition were exposed to four tarantulas: a di€erent spider for each exposure trial. In the CS condition, participants were exposed to the identi®ed control spider for all four exposure trials. Therefore, including the assessment spiders (one control, two novel), participants in the VS condition were exposed to a total of seven di€erent spiders, whereas participants in the CS condition were exposed to only three di€erent spiders. 2.4. Self-report measures 2.4.1. Watts and Sharrock Spider Phobia Questionnaire This measure (Watts and Sharrock, 1984) is a 43-item questionnaire found, with factor analysis, to contain subscales concerned with vigilance, preoccupation, and avoidance-coping. The scales have demonstrated good internal consistency and di€erentiate between phobic and non-phobic groups. 2.4.2. Intertrial Questionnaire This measure was designed for the purposes of the current experiment. Participants rate: (a) maximum anxiety during the task (0±8); (b) degree of perceived danger during the task (0±8); (c) perceived chance of being bitten by the spider (0±100%); and (d) severity ratings on a 13item panic symptoms checklist (0±8; DSM-IV checklist of panic symptoms; American Psychiatric Association, 1994). For all 0±8 scales in the investigation, 0 was equivalent to none/ not at all and 8 was equivalent to extreme/a lot.

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2.4.3. Metacognition Questionnaire This measure was also designed for the purposes of the experiment. This self-report measure assessed the participant's perception: (a) that his or her fear has decreased (0±8); (b) of the permanence of this reduction (0±8); (c) fearfulness if confronted with a spider outside of the experiment (0±8); and (d) fearfulness if asked to repeat the most recent task accomplished, in a few weeks (0±8). 2.5. Behavioral measures 2.5.1. Behavioral Assessment Test (BAT) During experimenter training, the spiders had occasionally become aggressive. Therefore, to eliminate risk to participants, they were instructed not to handle the tarantulas with their hands. Instead, participants touched a spider with a pencil and a q-tip on the abdomen and tips of the back legs. After modeling by the experimenter, participants were informed they would be asked to approach and touch the spider with a pencil for 2 min and a q-tip for 2 min. After obtaining a 0±8 subjective units of distress (SUDs) rating while participants stood 12 ft away, participants were asked to approach the container and touch the spider with the pencil. Immediately before touching the spider with the pencil, SUDs were again rated. After 2 min with the pencil, participants were asked to switch to the q-tip, and again SUDs were rated. Participants refusing to move to the next step were allowed to stay at their current position and instructed to attempt the next level as soon as they were able. 2.6. Physiological measures Heart rate was recorded continuously using a UNIQ Heart Rate Watch, consisting of an electrode belt worn around the chest from which heart rate signals were stored in a wrist receiver. Heart rate was sampled over 15-sec intervals. A built-in event marker enabled designation of di€erent experimental phases. The UNIQ system records heart rate with an accuracy of 21.00. Heart rate was recorded during pre-training, post-training, and follow-up BATs and all exposure trials. A 2-min baseline measure of heart rate was obtained following completion of the study to avoid measurement of anticipatory anxiety that may have confounded a pre-training baseline measure. 2.7. Exposure trials Each exposure trial was divided into seven 1-min steps. The seven steps were as follows: standing 12, 5, 2 and 0 ft away from the spider, placing one's face at the edge of the glass container, guiding the tarantula around with a pencil, and ®nally guiding the tarantula with a qtip. At the start of each new step, participants reported their SUDs rating. At each minute mark, participants were asked to move to the next step. If the participant refused to move to the next step, he or she remained at the current step. Exposure trials were identical for both conditions with one exception. In the CS condition, participants were exposed to the same

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spider encountered during the pretreatment BAT, whereas Ss in the VS condition were exposed to four di€erent spiders, none of which were encountered during the pretreatment BAT. 2.8. Procedure The study occurred over two sessions. The ®rst session included a pre-training assessment, four exposure trials, and two post-training assessment trials, and lasted approximately 2 hr. The second session occurred approximately 3 weeks after the ®rst session and included two follow-up assessment trials which lasted one-half hour. At the beginning of the ®rst session, participants completed the Watts and Sharrock Spider Phobia Questionnaire (1984). Next participants were asked to read a one-page information sheet on spiders, which provided basic information about the anatomy and behavior of spiders and proper ways of handling spiders. The experimenter reviewed this information with each participant. Following this, the ambulatory heart-rate monitor was attached and participants were instructed in its use. The pre-training BAT was then conducted with the designated control spider. Following this, four exposure trials were conducted. Each trial consisted of seven steps, each step lasting 1 min. Following each exposure trial, S s completed an Intertrial questionnaire. After the four exposure trials, two consecutive post-training BATs were conducted. One of the BATs involved the control spider and the other a novel spider. The order of the control and novel spider was counterbalanced across both groups and held constant for each yoked pair of S s. Along with an Intertrial Questionnaire, the Metacognition Questionnaire was distributed after the post-training and follow-up BATs. Finally, following the 2-min baseline, participants were debriefed.

3. Results 3.1. Pre-training analyses Independent-samples t-tests revealed no di€erences on pre-training measures of spider phobia (P > 0.05 for all measures; see Table 1). Neither baseline heart rate nor pre-training heart rate di€ered between groups (P > 0.05). To test for initial physiological activation, a 2  2 repeated-measures ANOVA was used to compare average baseline heart rate to average pretraining BAT heart rate. A main e€ect of time revealed a signi®cant increase in heart rate from baseline to pre-training BAT [F(1,26) = 4.70, P < 0.05], thus indicating signi®cant physiological activation. Because neither baseline heart rate nor pre-training BAT heart rate di€ered between groups, covariates were considered unnecessary for remaining heart-rate analyses. 3.2. Between-session analyses A series of 2  4 repeated-measure ANOVAs were conducted to examine fear reduction across the four exposure trials. Means and standard deviations of all measures are presented in Tables 2 and 3. To examine the pattern of between-session habituation in SUDs and heart

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Table 1 Means and standard deviations of self-report, physiological, and behavioral measures of fear in response to control spider at pre, post, and follow-up assessments Pre

CS condition SUDS anticipatory maximum HR bpm Time to approach using pencil using q-tip VS condition SUDS anticipatory maximum HR bpm Time to approach using pencil using q-tip

Post

Follow-up

n

M

SD

n

M

SD

n

M

SD

14 14 14

6.07 7.43 93.85

2.26 1.02 9.61

14 14 13

2.57 5.07 83.02

1.99 2.02 10.11

14 14 13

4.29 5.14 91.07

2.43 2.35 12.69

14 14 14

44.50 141.36 58.64

60.42 59.48 51.43

14 14 14

16.79 121.57 110.93

13.74 8.66 29.51

14 14 14

37.79 113.57 90.29

69.08 35.96 39.29

14 14 14

4.71 6.79 93.32

2.27 0.82 16.57

14 14 14

2.79 4.43 82.62

1.81 2.68 12.13

14 14 14

3.14 4.50 90.13

1.61 2.68 13.66

14 14 14

32.0 122.93 84.64

47.62 39.55 27.86

14 14 14

11.07 123.64 110.21

5.88 12.29 11.51

14 14 14

11.43 127.50 111.93

3.80 7.36 18.05

Note: CS = constant stimulus exposure condition. VS = variable stimulus exposure condition. SUDs = subjective units of distress, range 0±8 point scale. HR bpm = heart rate beats per minute. Cells with n < 14 indicates missing data.

rate, the seven steps of each trial were combined to form three stages as follows: anticipatory anxiety (step 1), approach (steps 2±4), and contact (steps 5±7). A main e€ect of time revealed signi®cant reductions in SUDs across trials (P < 0.001 for anticipatory anxiety, approach, and contact; see Table 2). As predicted, an interaction e€ect revealed participants in the CS group reported greater reductions in fear in the anticipatory [F(3,78) = 2.85, P < 0.05] and approach stage [F(3,78) = 2.94, P < 0.05]. In fact, simple-e€ects analyses revealed that VS participants failed to demonstrate signi®cant decreases in anticipatory anxiety across exposure trials whereas CS participants had signi®cant decreases in anticipatory anxiety [F(3,78) = 12.42, P < 0.001]. Simple-e€ects analyses of approach ratings did not detect signi®cant di€erences between groups within or across trials, although CS participants appeared to experience greater reductions in fear than VS participants. There was no signi®cant di€erence between groups in degree of fear reduction during contact with the tarantula. To analyze changes in heart rate, heart rate scores were averaged across time intervals corresponding to anticipatory anxiety, approach, and contact. Both groups showed a trend in heart rate reduction across trials for anticipatory anxiety [F(3,69) = 2.58, P < 0.06]. Both groups demonstrated signi®cant reductions in heart rate during the approach [F(3,66) = 5.52, P < 0.01] and contact with the tarantula [F(3,72) = 15.25, P < 0.001]. No interactions were detected.

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Table 2 Means and standard deviations of SUDs ratings of anticipatory anxiety, approach, and contact with spiders across four exposure trials

CS Anticipatory Approach Contact VS Anticipatory Approach Contact

n

Trial 1 M

Trial 2 M

Trial 3 M

Trial 4 M

14 14 14

3.43 (1.91) 5.19 (2.18) 6.55 (1.81)

2.50 (2.03) 3.86 (2.12) 5.74 (2.14)

2.00 (1.75) 2.83 (2.02) 4.98 (2.16)

1.36 (1.65) 2.26 (1.66) 4.33 (2.06)

14 14 14

3.34 (1.65) 4.71 (1.61) 6.38 (1.05)

2.71 (1.69) 3.93 (2.03) 5.81 (1.47)

3.00 (2.22) 3.50 (2.20) 4.91 (2.41)

2.50 (1.65) 3.17 (2.11) 4.50 (2.68)

Note: CS = constant stimulus exposure condition. VS = variable stimulus exposure condition. SUDs = subjective units of distress, 0±8 point scale ranging from none (0) to extreme distress (8). Anticipatory = SUDs rating at 12 ft away from spider. Approach = average SUDs rating across three distances: 5, 2 and 0 ft away from spider. Contact = average SUDs rating across three tasks: chin at edge of container, touching spider with pencil, then with q-tip.

Finally, both groups demonstrated signi®cant decreases in reported physiological symptoms, ratings of danger, and percentage estimates of chance of being bitten (P < 0.05 for all measures) across the four trials. No interactions were detected for these measures either. 3.3. Pre to post BAT analyses A series of 2  2 repeated-measures ANOVAs were conducted to analyze pre-training to post-training changes. Means and standard deviations of post-training measures are presented in Table 1. Comparing groups from pre-training to post-training BAT performance with the control spider revealed equivalent and signi®cant decreases in fear for both groups with one Table 3 Means and standard deviations of self-reported physiological symptoms, danger ratings, and percentage estimates of bite by spider across four exposure trials

CS Physio. sx. Danger Percent est. VS Physio. sx. Danger Percent est.

n

Trial 1 M

Trial 2 M

Trial 3 M

Trial 4 M

14 11 13

34.00 (17.88) 5.09 (2.43) 23.15 (24.83)

25.64 (16.74) 4.36 (2.58) 17.23 (26.70)

23.07 (16.24) 4.00 (2.86) 19.77 (27.08)

17.57 (15.94) 3.64 (2.50) 10.08 (13.14)

14 13 14

36.36 (21.60) 5.46 (1.39) 41.00 (31.09)

35.64 (22.47) 5.08 (2.18) 41.21 (31.77)

33.36 (24.56) 4.70 (2.72) 34.14 (34.43)

27.29 (20.72) 4.15 (2.23) 27.79 (36.17)

Note: CS = constant stimulus exposure condition, VS = variable stimulus exposure condition. Physio. sx. = selfreported physiological symptoms, range 0±104. Danger = danger ratings, range 0±8. Percent. est. = percentage estimate of acquiring bite by spider, range 0±100. Cells with n < 14 indicates missing data.

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exception. Amount of time spent touching the tarantula with a pencil did not change. This change can be explained methodologically. Because time spent moving from 12 ft away to using the pencil decreased signi®cantly from pre to post-training [F(2,61) = 5.70, P < 0.05] and time spent touching the tarantula with a q-tip increased signi®cantly [F(1,26) = 19.40, P < 0.001], time spent touching the tarantula with a pencil could not signi®cantly increase or decrease as the total amount of time allowed for this task was constrained by the beginning and end points of the BAT. Heart rate, SUDs ratings of anticipatory anxiety and maximum fear, and self-reported physiological symptoms all decreased signi®cantly for both groups from pre to post-training (all measures P < 0.001). Decreases in ratings of danger [F(1,24) = 9.92, P < 0.01] and percentage estimates of being bitten [F(1,26) = 7.50, P < 0.05] were apparent for both groups. No interaction e€ects were revealed with the exception of a trend for individuals in the CS group to demonstrate a greater reduction in reported anticipatory anxiety [F(1,26) = 3.20, P = 0.085; see Fig. 1]. A series of t-tests on the Metacognition Questionnaire revealed a signi®cant di€erence in the degree to which individuals thought the training would generalize to spiders outside of the experiment. Individuals of the CS group reported that they would be more fearful of spiders outside of the experiment than individuals in the VS group (t = 2.11, P < 0.05). No di€erences were detected on perceived degree of fear reduction, permanence of reduction, or prediction of fear on future tasks. An additional question at the end of the Metacognition Questionnaire requested individuals to report the number of tarantulas they had seen during the experiment. Although individuals in the VS group were not completely accurate, they clearly recognized that they had worked with a variety of tarantulas (M = 5.74, SD = 2.09) compared to individuals in the CS group (M = 2.00, SD = 0.55) who were also not completely accurate. 3.4. Post to follow-up BAT analyses A series of 2  2 repeated-measures ANOVAs were conducted to analyze post-training to follow-up changes. Means and standard deviations of all measures are presented in Table 1. Interestingly, measures of anticipatory anxiety [F(1,26) = 9.29, P < 0.01] and heart rate [F(1,25) = 12.36, P < 0.01] revealed main e€ects of time from post to follow-up BAT when tested with the control spider. Furthermore, there was a group  time interaction trend for anticipatory anxiety [F(1,26) = 3.99, P < 0.056]. Simple-e€ects analyses revealed that participants in the CS group demonstrated a signi®cant increase in anticipatory anxiety from post to follow-up [F(1,26) = 12.72, P < 0.01] whereas VS participants did not (see Fig. 1). Measures of time, maximum SUDs, self-reported physiological symptoms, danger ratings, and percentage estimates revealed no di€erences between post BATs and follow-up BATs for the control spider (see Table 2). By follow-up, results on the Metacognition Questionnaire changed substantially. Both groups demonstrated signi®cant improvements in ratings of permanence of fear reduction due to training [F(1,26) = 7.88, P < 0.01] and lowered their estimates of how fearful they would be if they had to repeat the BATs in 3 weeks [F(1,26) = 6.53, P < 0.05]. Additionally, there was a trend for individuals in the CS group to decrease ratings of how fearful they would be of spiders

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Figure 1. Comparison of constant stimulus (CS) condition vs variable stimulus (VS) condition on ratings of anticipatory anxiety across pre, post, and follow-up assessments with the control spider.

outside of the experiment [F(1,26) = 3.59, P < 0.07] such that they were no longer signi®cantly di€erent than individuals in the VS group on this question. At the end of the questionnaire, participants were asked to report whether or not they had come in contact with a spider since the training session. Chi-square analysis revealed no di€erences in number of participants in the CS group (yes = 5, no = 9) vs those in the VS group (yes = 3, no = 11) who had contact with a spider since training. 3.5. Generalization analyses To analyze generalization of fear reduction and detect possible ROF in response to a novel stimulus, BAT measures of the novel tarantulas were compared to BAT measures of the control tarantula at post and follow-up in a series of 2  2 repeated-measures ANOVAs. As a

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Table 4 Means and standard deviations of self-report, physiological, and behavioral measures of fear in response to novel spiders at post and follow-up assessments Post control

CS condition SUDS anticipatory maximum HR bpm Time to approach using pencil using q-tip VS condition SUDS anticipatory maximum HR bpm Time to approach using pencil using q-tip

Post novel

Follow-up control Follow-up novel

n

M

SD

M

SD

n

M

SD

M

SD

14 14 13

2.57 5.07 83.02

1.99 2.02 10.11

3.71 5.79 84.81

2.16 1.97 10.16

14 14 14

4.29 5.14 91.07

2.43 2.35 12.69

4.43 5.71 94.25

2.47 2.27 12.86

14 14 14

16.79 121.57 110.93

13.74 8.66 29.51

34.22 116.29 91.86

61.88 35.46 40.38

14 14 14

37.79 113.57 90.29

69.08 35.96 39.29

28.64 118.14 100.43

61.10 35.36 30.77

14 14 14

2.79 4.43 82.62

1.81 2.68 12.13

2.93 4.93 85.66

2.09 2.62 12.92

14 14 14

3.14 4.50 90.13

1.61 2.68 13.66

3.57 5.64 91.65

2.17 2.62 13.09

14 14 14

11.07 123.64 110.21

5.88 12.29 11.51

13.00 123.29 109.07

5.23 14.00 12.72

14 14 14

11.43 127.50 111.93

3.80 7.36 18.05

13.57 126.29 109.43

4.42 4.29 17.13

Note: CS = constant stimulus exposure condition. VS = variable stimulus exposure condition. SUDs = subjective units of distress, range 0±8 point scale. HR bpm = heart rate beats per minute. Cells with n < 14 indicates missing data.

further analysis of possible di€erences in generalization, novel post BAT results were compared to novel follow-up BAT results. Means and standard deviations are presented in Table 4. At post BAT, the sample did not demonstrate a signi®cant increase in anticipatory anxiety in response to the novel spider, relative to the control spider, but did report signi®cantly more maximum fear [F(1,26) = 5.13, P < 0.05]. Heart rate also increased signi®cantly during the novel post BAT [F(1,25) = 20.95, P < 0.001]. Similarly, self-reported physiological symptoms demonstrated a signi®cant increase overall [F(1,26) = 4.67, P < 0.05]. Time spent at each step of the novel BAT was not signi®cantly di€erent than during the control BAT. Danger ratings and percentage estimates of being bitten did not change in response to the novel tarantula. No interactions were detected. At the follow-up BAT, neither group demonstrated an increase in anticipatory anxiety in response to the novel spider, relative to the control spider, but again revealed a signi®cant increase in maximum fear [F(1,26) = 8.21, P < 0.01]. As at post, heart rate increased [F(1,23) = 4.79, P < 0.05], but self-reported physiological symptoms did not change. Time spent at each step of the BAT was not signi®cantly di€erent than during the control BAT. Ratings of danger signi®cantly increased [F(1,25) = 5.68, P < 0.05], but percentage estimates of being bitten did not change. No interactions were detected.

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No main e€ects nor interaction e€ects were detected for any measures in the comparisons of novel post BATs to novel follow-up BATs.

4. Discussion Results of the current investigation provide moderate support for the proposed hypotheses. It was predicted that participants in the CS group would demonstrate a signi®cantly greater rate of habituation across exposure trials compared to participants in the VS group. This was hypothesized to be indicated by greater decreases in self-reported fear, heart rate, and ratings of physiological symptoms. This prediction was based on the assumption that varying the stimuli presented in the VS group would retard habituation compared to the CS group, as novel stimuli typically generate dishabituation. The predicted e€ect occurred in the self-report of fear for anticipatory anxiety and fear reported during the approach to the spider, but not during contact with the spider. Although there was no di€erence in degree of habituation as re¯ected in heart rate or self-reported physiological symptoms, the failure of physiological measures to correspond to self-reports of fear is a common ®nding in exposure paradigms (see Lang, 1971; Rachman and Hodgson, 1974), especially at lower levels of arousal (e.g. Borkovec, 1973, 1974). Nevertheless, the lack of physiological reactivity to the novel spiders during VS exposure is surprising as it was clearly present during post and follow-up assessments. At post assessment, dishabituation in heart rate and self-reported physiological symptoms occurred in both groups in response to the novel test spider. At follow-up, dishabituation occurred in heart rate, although self-reported physiological symptoms did not increase. Greater physiological reactivity during BATs compared to exposure trials may have resulted from the greater demand of the BAT protocols. Contact with the spider was limited to 2 min during exposure trials, whereas participants were expected to touch the spiders with the pencil and q-tip for approximately 4 min during the BAT assessments. Although di€erential habituation was not evident in physiological measures, a di€erential decrease in self-reported fear re¯ects degraded training performance and may indicate di€erent information processing activity. Therefore, as predicted, the CS condition appeared to result in greater fear reduction across exposure trials compared to the VS condition. It was further hypothesized that participants in the CS condition would perform better at the post assessment with the control spider, but exhibit more ROF in response to the novel spider than VS participants. On the majority of self-report, physiological, and behavioral measures, both groups performed equally well in response to the control test spider and equally poorly in response to the novel test spider. However, there was some evidence that CS participants performed better: a trend showed that CS participants reported lower levels of anticipatory anxiety in response to the control spider. The bene®ts of conducting exposure with a variety of spiders were predicted to appear at the follow-up assessment. Group di€erences in anticipatory anxiety in response to the control spider best characterized the predicted pattern: degraded performance for VS participants during exposure trials and at post assessment with the control spider, but superior maintenance at follow-up. This supports Bjork and Bjork's (1990) New Theory of Disuse. Although the added `diculty' of varying the stimuli degraded the progress of VS participants during training, in

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the long-term, this process of continual readjustment to varying stimulus information led to less ROF than that seen in the CS group. This pattern also provides discon®rming evidence regarding Foa and Kozak's (1986) emotional-processing model. In keeping with the stipulations of their model, both groups demonstrated signi®cant initial physiological activation. Both groups demonstrated physiological habituation. Furthermore, CS participants evidenced signi®cantly greater between-session habituation in self-reported distress than VS participants. The greater between-session habituation for CS participants compared to VS participants would predict more ROF for the VS group, and yet the converse was true. Indeed, the one measure that did not reveal habituation across exposure trials for the VS group (i.e. anticipatory anxiety) was the measure that most distinguished superior treatment outcome between groups at follow-up. At follow up, both groups evidenced signi®cant ROF in maximum fear and heart rate in response to the novel spider. This indicates that both groups responded more fearfully to the novel spider than the control spider. These results at follow-up demonstrate the powerful e€ects of time and context as predicted by Bjork and Bjork (1990) and Bouton and Swartzentruber (1991). Shifting context cues, including stimulus cues, can abruptly trigger older, fearful learning. In Bjork and Bjork's (1990) model, this would be explained as less retrieval strength in the face of competing retrieval cues with greater storage and retrieval strength. According to Bouton (1988), this would be explained by the context speci®city of extinction. As stated earlier, the prediction of Bjork and Bjork (1990) and Bouton and Swartzentruber (1991) appear to contradict those of Foa and Kozak's (1986) emotional-processing model of fear reduction. As suggested by Rachman (1979), if ROF can be viewed as insucient emotional processing, then the results of this investigation indicate a de®nite lack of emotional processing. Yet, according to Foa and Kozak's (1986) model, very little, if any, ROF should have resulted. Both groups demonstrated signi®cant decreases in self-report of fear and physiological measures of fear across trials. Finally, both groups evidenced changes in probability of harm and valence of danger. In fact, changes in meaning of the stimulus appeared to endure at post and follow-up assessments, despite ROF in self-reported fear and autonomic responding. According to Foa and Kozak's (1986) model, changes in probability of harm and valence are products of successful habituation. The apparent discrepancy between predictions of Foa and Kozak's (1986) model and results of this investigation recall the admonition of Schmidt and Bjork (1992) that acquisition performance is not an accurate indicator of learning. In reviewing multiple investigations from the motor learning and cognitive literature, they conclude that e€ectiveness of learning is revealed by level of retention shown over time in post-training performance and generalization to related tasks and contexts. This approach argues strictly against the use of performance measured during training to predict endurance of training. In many cases, added diculties during training suppress training performance, but prepare the learner for later shifts in tasks and contexts when the training will actually be tested. Varying the task is a manipulation that should result in better retention and transfer of learning as it forces the learner to retrieve and organize a slightly di€erent set of information on every trial. Although support for the bene®ts of increased variability in training appears modest, this may be a function of inadequacies of the study design and measurement procedures. The

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variability manipulation may have been more potent if the spiders had included other species besides tarantulas. Additionally, varying the type of task or context may produce more robust results than varying the stimulus features (Bouton, 1988). If exposure trials were increased to allow for greater habituation during the contact phase, di€erences in rates of habituation during this phase and ROF at follow-up may have become more apparent. Additionally, the lack of an approach phase in the BATs rendered it impossible to analyze fear responses at distances comparable to those in the approach phase of the exposure trials. Therefore, it is unclear whether a similar ROF pattern may have been detected in the CS group if the BATs had an approach phase. If tests of generalization had not been included in this investigation, the degree of ine€ectiveness of the exposure protocol would have been undetected. These results reinforce Schmidt and Bjork's (1992) advocacy of various kinds of transfer and retention tests to properly evaluate training e€ectiveness. Although some research has investigated the transfer of fear reduction from one type of phobia to another (e.g. Cotler and Garlington, 1969; Williams et al., 1989), tests of generalization have not been systematically included in investigations of ROF. The intention of measuring participant's perceptions of their improvement and generalization of improvement was to parallel metamemory investigations of other training paradigms. Bjork (1994) proposes that a major contributor to non-optimal training is the learner's mis-reading of his or her progress during training. The results of the Metacognition Questionnaire illustrates this well. After demonstrating ROF to both the control and novel test spiders at the follow-up assessment, participants proceeded to increase their ratings of perceived permanence of fear reduction, lower their predictions of fear to the same tasks in the future, and maintained ratings of overall fear reduction and generalizability of fear reduction due to the training experience. In other words, participants perceived continued improvement despite substantial evidence to the contrary. The comparable ratings of the two groups despite greater anticipatory anxiety in the CS group at follow-up may suggest increased vulnerability for future relapse in the CS group. Although measures of self-reported fear and physiological change indicated ROF at followup, notably, behavioral changes were stable. Participants may have based their self-assessments of progress primarily on behavioral change. One distinct di€erence between cognitive and motor learning vs learning that occurs during fear reduction is the minimal focus on skill acquisition and the maximal focus on e€ort. Willingness of the individual to be in the presence of the feared stimulus is half the battle. Participants demonstrated signi®cant decreases in approach time and increases in contact time from pre to post-training and follow-up assessments. These gains were stable across time and type of stimulus. The results of the current investigation provide modest support for the bene®ts of incorporating variability into an exposure protocol. Although the predicted pattern of results was obvious only in anticipatory anxiety, increasing the number of trials and altering the assessment procedure may elucidate a similar pattern in maximum fear and autonomic response. Also, greater anticipatory anxiety may ultimately lead to more phobic avoidance. The inclusion of tests of generalization to assess the e€ectiveness of treatment illustrates the need for the routine inclusion of tests of transfer, as advocated by Schmidt and Bjork (1992). Finally, results

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clearly challenge the reliance on indices of fear activation and within and between-session habituation as accurate signals of the permanence of fear reduction.

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