An investigation of the effectiveness of desensitization and flooding with two types of phobias

Bchav Ren & Therapy. 1971. Vol

IS. pp 23-30

Pergamon Press. Prmted m Great Bntam

AN INVESTIGATION OF THE EFFECTIVENESS AND FLOODING OF DESENSITIZATION WITH TWO TYPES OF PHOBIAS KJELL ERIK RUDESTAM York University. Downsview. Ontario M3J lP3. Canada

and RICHARD BEDROSIAN Miami University. Oxford. Ohio. U.S.A. (Received 27 JUIW

1976)

Summary-Thirty-two university undergraduates. sixteen complaining of specific phobias and sixteen suffering from social phobia, were treated using either desensitization or flooding procedures. The effectiveness of therapy was evaluated using physiological. self-report. and objective test data. Heart rate and GSR responses to both phobic and neutral slides and images, and habituation rate to neutral tones. were obtained for each subject. Physiological changes were greatest using flooding, especially with specific phobics. while other measures, including therapist and client satisfaction, supported desensitization. Results are consistent with a model stressing the need for a repeated exposure to specific fear cues.

Both systematic desensitization and flooding (implosion) have been shown to exhibit impressive success in treating phobic disorders in various contexts. In some instances desensitization procedures have been more effective (c.f. Mealiea and Nawas, 1971; Cornish and Dilley, 1973; Rachman, 1966) while in other studies flooding techniques have produced a superior outcome (c.f. Boulougouris, Marks and Marset, 1971; Boudewyns and Wilson, 1972). In spite of this success, the mechanisms underlying the effectiveness of the two approaches are not well understood. Procedurally, gradually presenting anxiety stimuli to a client who is in a state of deep muscular relaxation, as in desensitization, seems antithetical to deliberately bombarding the client with fear arousing stimuli until his anxiety extinguishes, as in flooding. It has been suggested, however, that a similar theoretical rationale may in fact underlie both procedures, viz. that habituation accounts for a response decrement in anxiety in both flooding and systematic desensitization, since desensitization might be conceptualized as habituation when the level of autonomic arousal is low and the habituation rate is maximal. To the extent that therapeutic success involves a decrease in the autonomic component of anxiety, the relative effectiveness of the two techniques may be a function of certain individual differences in autonomic functioning. Another predictor related to the relative utility of the two therapy approaches might be the type (or intensity) of phobia. It has been shown, for instance, that habituation of an autonomic response such as GSR to auditory stimuli is faster for subjects with a specific phobia than with agoraphobics (Lader and Mathews, 1968). One might speculate that prior conditioning of anxiety is crucial to the etiology of specific phobias, whereas a chronic state of overarousal is more likely to be the case in agoraphobias. In the present study subjects (Ss) with either a specific phobia, e.g. small animal fears, or social phobia or agoraphobia. a more diffuse anxiety state, participated in either systematic desensitization or flooding. In line with the notion that anxiety involves many different, sometimes independent, response systems (c.f. Lang, 1971; Leitenberg, Agras, Butz and Wincze, 1971) Ss were measured both before and after treatment on three self-report tests of anxiety and on the physiological measures of GSR and heart rate. Moreover, in an attempt to isolate psychophysiological predictors of treatment efficacy, Ss were exposed both before and after therapy to phobic and neutral slides 23

24

KJELL ERIE RL.DESTAMand RICHARD BEDROSIAS

and images and a series of neutral tones while these measures were monitored. Finally. both Ss and therapists were assessed at the conclusion of treatment as to their views of therapy effectiveness. Based on previous work it was predicted that Ss would exhibit increased autonomic arousal to phobic stimuli and that those Ss showing the greatest heightened physiological activity would be most responsive to treatment. Since studies ‘have not demonstrated clear differ&es in outcome between systematic desensitization and flooding. it was thought that individual differences, such as autonomic responsivity and type of phobia. might mediate such effects. Specifically, one might expect desensitization to be more effective when autonomic arousal related to the phobic scene is increased the most (such as in more easily visualized and imagined specific phobias). since such arousal would encourage maximal habituation. Moreover. one would not expect physiological indices to decrease as readily for social phobics or agoraphobics who are characterized by a more-or-less chronic state of overarousal. If there were adequate repetition of phobic scenes, flooding techniques might be more effective with these clients. since these procedures do not appear to require the same autonomic responsivity or habituation rate. METHOD

Subjects

All subjects were undergraduate students, between 18 and 22 years of age. They were recruited through the use of posters and advertisements in the student newspaper. To insure continuation in therapy, all subjects received $10 for their participation, payable at the end of treatment. (a) Subjects with specijic phobias. Specific stimuli provoked fear in these 16 subjects. Six subjects feared snakes, six feared spiders. one rats, one bees, one dogs, and one cockroaches. (b) Subjects with social phobias. Social situations including crowds, public speaking, etc. were fear-provoking for these 16 subjects. Procedure and measures

(a) Psychometric assessment. Subjects were administered the Wolpe-Lang Fear Survey Schedule, Repression-Sensitization Scale, and the IPAT Anxiety Scale, both before and after treatment. As part of the post-therapy assessment, each client and each therapist were asked to answer the following questions on a graphic 5point scale, ranging from “not at all”, to “very much”: (1) To what extent was the treatment effective in reducing fear in the session?; (2) To what extent was the treatment effective in reducing fear outside the session?; (3) How well did you like your therapist (client)? (b) Psychophysiological assessmetlt. Following administration of the psychometric devices. subjects were taken to an 8 x 12-foot room which contained a padded couch, slide projector, earphones, and intercom. EKG electrodes were placed around both wrists and the left ankle; GSR was recorded from two electrodes on the right thumb and forearm (Lader and Wing, 1966). Subjects were asked to put on the earphones and relax on the couch while the experimenter left to operate the polygraph in an adjacent hallway. A Grass Model 7 polygraph was used for the physiological recordings. EKG signals were fed through a Grass 7P4D Tachograph. As soon as a stable baseline recording was obtained. the first of twenty habituation trials was begun. Each subject received through the earphones, twenty 100-dB. 1000 khz tones. generated by a Hewlett-Packard Audio Oscillator. The intervals between the tones, ranging from 40 to 80sec, were randomly selected by computer. A rest period of 2 min followed the last tone. Towards the end of the rest period, subjects were told that they would shortly be viewing some slides. The first slide, a neutral one, was shown for 30 sec. After a wait of 1 min, a phobic slide was presented for 30 sec. Subjects with specific phobias were shown closeups

Effectiveness

of desensitization

and flooding

with two types of phobias

25

of the appropriate animals, while social phobics were shown slides of crowds or audiences. The phobic slide was followed by a rest of 1 min. Subjects were then asked to visualize a predetermined neutral image for 30 sec. A rest period of 1 min ensued, after which the subjects were asked to visualize a prearranged phobic image for 30 sec. Physiological recordings continued for 2 min after the termination of the phobic image. Post-treatment psychophysiological assessment was conducted in an identical fashion. except that the habituation trials were omitted. The following physiological measures were taken on each subject: (1) Resting heart rate. This measure, obtained during the pre-treatment assessment. was the mean heart rate during the ten second period prior to the presentation of the neutral slide. (2) Heart rate during slides and images. Mean heart rate was calculated for the lo-set intervals between the fifth and fifteenth seconds of stimulus presentation. This measure of heart rate produced correlations in excess of 0.95 with the mean heart rates for the entire 30-set stimulus presentation. (3) Heart rate change in response to slides and images. This measure reflected the difference in mean heart rate between the lo-set intervals prior to and during the slides and images. (4) Resting skin resistance. Skin resistance, in ohms, was obtained just prior to the presentation of the neutral slide. (5) Galvanic skin response to tones, slides, and images. This measure was calculated from changes in log skin conductance before and after stimulation (Lader and Wing. 1966). (6) Habituation rate. Following Lader and Wing (1966), the rate of decrease of GSR’s to the second through twentieth tone stimuli was calculated. Subjects whose habituation rate reached statistical significance (p < 0.05) were designated as “habituators”, all others as “non-habituators”. (c) Treatment Procedure. Each subject was randomly assigned to either treatment by systematic desensitization or flooding after assessment was completed. Therapists were eight advanced graduate students in clinical psychology, each trained in both procedures. Each therapist offered both techniques and treated a client with each type of phobia, i.e. four cases per therapist. Subjects were seen for a total of six treatment sessions and then re-assessed by an experimenter unfamiliar with the assignment to treatment conditions. Systematic desensitization consisted of training in deep muscle relaxation, construction of anxiety hierarchies, and imaginal presentation of the anxiety stimuli while the subject was in a relaxed state. The flooding procedure also utilized an anxiety hierarchy, but no instructions in relaxation. Anxiety stimuli were presented imaginally and elaborated upon in order to evoke and extinguish the anxiety response. RESULTS

As expected, the more severe and diffuse anxiety of the social phobics was reflected in pretreatment differences on the Repression-Sensitization Scale (F = 16.21, p < 0.01) and the Fear Survey Schedule (F = 28.94, p < 0.01). Scores on the IPAT, although not statistically significant. were also in the predicted direction (F = 3.17, p < 0.083). Moreover, only the social phobics changed significantly on the Repression-Sensitization Scale (t = 2.81 and t = 2.49. p < 0.05) and these improvements occurred regardless of method of treatment. Both client and therapist ratings at the conclusion of treatment attest to the effectiveness of the therapy procedures. Clients, on the average, rated their therapy as successful in reducing fears within sessions (S = 3.72) and outside sessions (Z = 3.15) and liked their therapists (X = 4.34). Therapists, on the average, saw the treatment as successful within sessions (X = 3.44) and outside sessions (X = 2.97), and liked their clients (X = 3.88). Both Ss and therapists viewed systematic desensitization as somewhat more effective than flooding (clients: X = 3.87-3.61; therapists: X = 3.51-3.35). Therapists, in

26

KJELL ERIP RUDESTAM and RICHARD BEDROSIAN

particular, concluded that desensitization was especially effective with specific phobias. and that flooding with social phobias was the least rewarding treatment. A 2 x 2 Analysis of Variance (Treatment x Phobia) on pretreatment resting heart rates found that heart rates were significantly higher for specific phobics than social phobics (F = 6.01, p < 0.05). There were no other significant main effects nor interactions in this analysis. Average heart rates were computed for the lo-set intervals prior to and during presentation of phobic slides and images before and after therapy. Two way Analyses of Variance (Treatment x Phobia) were computed on the change scores to determine the impact on heart rate of phobic stimuli both before and after therapy. A “change of a change” measure was computed to determine if the phobic stimuli had less of an impact on Ss after therapy concluded. Results of the Analyses of Variance indicated that the effects of the phobic slides on heart rate were greater for specific phobics than social phobics prior to treatment (F = 5.12, p < 0.05). There were no other group differences. Moreover. no group was differentially more or less affected by the slides after treatment The phobic images also resulted in significantly greater heart rate arousal for specific phobics than social phobics prior to treatment (F = 4.43, p < 0.05). There were no significant post-therapy differences. However, there was a significant main effect for type of phobia on the change of the change scores for images (F = 4.35. 17 < 0.05). indicating that the effect of treatment was greatest for the specific phobics on this measure. A subsequent analysis of this result revealed that the greatest reduction in heart rate arousal occurred for the specific phobic treatment using flooding procedures (t = 3.80. p < 0.01). A summary of the Analyses of Variance appears in Table 1. Two-by-two Analyses of Variance (Treatment x Phobia) were computed on change scores for GSR responses to phobic slides and images. Results for the slides indicated a significant main effect for treatment, with a decrease in skin resistance for Ss receiving systematic desensitization and an increase in resistance for Ss receiving flooding (F = 10.29, p < 0.01). Likewise. for the impact on phobic images. Ss who participated in flooding decreased on GSR significantly, while those who received desensitization did not change (F = 6.20, p < 0.05). It is also true, however. that GSR values were not uniformly distributed among groups prior to treatment. Consequently. pre-post changes were compared within each phobia between treatments. In this way one finds a relative decrease for social phobics with flooding over systematic desensitization on slides (r = 2.30, p < 0.05). and for specific phobics with flooding over systematic desensitization on slides (t = 2.08, almost p < 0.05) and images (t = 2.47, p < 0.05). Another indication of the impact of flooding on GSR responses is that although all groups increased in resting skin resistance with treatment, the post-therapy resting skin resistances were significantly higher for those who had participated in flooding (F = 8.54, p < 0.01). while the specific phobics who experienced flooding were highest of all. A summary of the analyses on GSR responses can be found in Table 2. Table 3 provides an overview of the means of the major measures. both before and after Treatment. GSR recordings were also obtained during the pre-therapy presentation of 20 neutral tones. A regression line for tone habituation was computed for each S using a multiple x Phobia) revealed linear regression analysis. A 2 x 2 analysis of variance (Treatment no significant differences between the B values of these regression lines. Nor was rate of habituation a significant predictor of any other index of treatment success. However, when Ss were split into two equal groups on the basis of their self-report ratings of treatment effectiveness, Ss with the best therapy outcome could be distinguished by their pre-therapy GSR to phobic images (significantly lower values for good Ss, t = 2.21, p < 0.05). There were no significant relationships between treatment effectiveness and GSR to phobic slides. however. A correlation matrix was computed to investigate the relationships between all available dependent measures. This analysis reflected the congruence, first of all, of the three self-report measures, with the FSS, IPAT, and R-S Scale all correlating beyond the 0.05 level of confidence both before and after therapy. Physiological measures did not

Effectiveness

of desensitization

and flooding

with two types of phobias

27

Table 1. Results of analyses of variance evaluating heart rate changes by treatment (A) and phobia (B) (weighted analyses for unequal N)

ss

df

Source

F

MS

Heart rate changes to phobic slides prior to therapy A 1 6.82 6.82 0.13 B 1 251.55 251.55 5.12 A*B 1 71.46 71.46 1.42 Residual 26 1308.59 50.33 Heart

rate changes

Source A B A*B Residual Changes

to phobic df 1 1 1 26

in effects of phobic

images

ss

df

Source A B A*B Residual

1 1 1 26

images

ss 14.42 387.36 32.61 2273.28

9.30 371.00 14.09 2219.68

prior

p < 0.05

to therapy F 0.16 4.43 0.37

MS 14.42 387.36 32.61 87.43 on heart

p < 0.05

rate before and after therapy

MS 9.30 371.00 14.09 2219.68

F 0.11 4.35 0.17

p < 0.05

correlate’ significantly with self-report measures, with a few exceptions: a correlation of 0.38 between the FSS and GSR to phobic slides; a correlation of 0.36 between post-test IPAT and post-test resting skin resistance; and correlations between resting heart rate prior to treatment and RS both pre-(r = 0.45) and change (r = 0.64) and with change in IPAT (r = 0.39). A number of physiological measures were significantly intercorrelated: heart rate change to phobic slides correlated with post-therapy GSR’s to phobic slides (r = 0.43) and images (r = 0.45); the B-value of the habituation regression line correlated 0.47 with resting heart rate prior to treatment and -0.39 with post-therapy GSR to phobic images. Finally, correlations were generally significant between GSR responses to slides and images and client and therapist ratings of treatment effectiveness. A summary of intercorrelations among major measures is found in Table 4.

Table 2. Results of analyses treatment (A) and phobia

df

Source GSR changes A B A*B Residual

1 1 1 27

GSR changes Source A B A*B Residual Resting Source A B A*B Residual

to phobic

to phobic

df 1 1 1 21 skin resistance

df 1 1 1 27

of variance evaluating (B) (weighted analyses

ss

GSR changes for unequal N) F

MS

slides before and after therapy 0.15 0.001 0.05 0.41 images

0.15 0.001 0.05 0.02

10.28 0.08 3.15

p < 0.01

before and after therapy

ss

MS 0.05 0.21 0.03 0.008

0.05 0.21 0.03 0.21

F 6.20 3.58 1.42

p < 0.05

after therapy

ss 15475 258 7442 48910

x x x x

MS 106 15475 x lo6 lo6 258 x lo6 lo6 7442 x lo6 lo6 48910 x lo6

F 8.54 0.14 4.11

p < 0.01 p < 0.05

28

KJELL ERIK RUDESTAM and RICHARD BEDROSIAN

Table

3. Mean

values

on major

measures

before and after treatment

Pre-therapy

Wolpe-Lang FSS R-S Scale IPAT Heart rate-Slides Heart rate-Images GSR-Slides GSR-Images Client self-report: within therapy outside therapy liked therapist Therapist rating: within therapy outside therapy liked client

Post-therapy

SD specific

SD social

Flooding specific

Flooding social

SD specific

SD social

Flooding specific

Flooding social

1.75 24.75 30.88 81.57 85.44 0.036 0.042

2.27 37.88 42.13 76.13 80.84 0.038 0.027

1.70 24.13 39.50 83.38 88.16 0.164 0.148

2.53 31.75 43.38 66.26 70.14 0.046 0.052

1.66 22.25 27.12 74.67 75.89 0.161 0.023

1.94 35.13 39.88 72.11 14.09 0.061 0.015

1.56 26.13 42.00 70.87 73.67 0.062 0.003

2.18 32.38 40.13 60.58 62.40 0.023 0.004

3.71 3.14 4.20

4.00 3.50 4.50

3.67 3.00 4.00

3.50 3.00 4.50

3.86 2.86 4.29

3.50 3.13 3.50

3.56 3.11 3.78

2.88 2.75 4.00

DISCUSSION

There is a growing impression from the literature that neither systematic desensitization nor flooding are markedly superior to one another with all clients or, for that matter, on all outcome measures. Evidence has accumulated, for instance, to show that there is no isomorphic relationship between physiological and behavioral anxiety measures. That is, whether or not a phobic subject changes on physiological indices of anxiety may be a function of somewhat different variables than those that influence changes in behavior and self-report. One of the key variables indicated by the present study as underlying the success of physiological change from both desensitization and flooding techniques is the repeated exposure to specific fear cues. The present study found that both heart rate arousal and GSR arousal decreased more for specific phobics than social phobics. This is probably due to the fact that it was easier to present relevant stimulus material that captured the essence of specific phobias. That these changes were greatest in imagery (as opposed to slides) reflects the opportunity and need for Ss to visualize uniquely upsetting phobic cues. If habituation is indeed the central feature of both treatment procedures. this result becomes consistent with the finding of Lader, Gelder and Marks (1967) of a more rapid habituation rate for specific phobics than social phobics or agoraphobics, and with Klorman’s (1974) recent discovery that habituation is facilitated by highly intense visual stimuli. Along these lines, Denny (1975) has recently suggested that the treatment of generalized anxiety might necessitate increasing anxiety way beyond base level, so that relief and relaxation are inevitable after the removal of the aversive stimulus, since some fear may have been previously conditioned to relaxation-produced stimuli. It was also true in the present investigation that specific phobics had more heart rate and GSR arousal prior to therapy than other phobics and were initially more sensitive to phobic stimuli. This is in line with Mathews’ (1971) review, which concluded that Ss who are more responsive physiologically make a better response to treatment. On the other hand the study did not replicate the finding of Lader ef al. (1967) that rapid habituation to neutral tones can be used as a predictor of favorable treatment outcome. It was also found that flooding had a greater impact on physiological measures than desensitization, which appears inconsistent with a number of investigators (c.f. Boulougouris, Marks and Marset, 1971) who have found desensitization to be particularly successful with specific phobics. However, the same group (Marks, Boulougouris and Marset, 1971) have found that flooding is superior with the most anxious Ss and it

ml

0 77’ I.CQ

FSS2

064’ 1.m

osn*

IPA

0 53. 050. 0 82’ loo

IPB

0.6X’ 0.61’ 0.70’ 0 549 If@

RSI 0 62’ 0.63. 0 X2’ 0.79* 0w 1w

RS? 0.24 0.23 - O.M 0.09 0.04 - 0.w IM)

PRES 007 0.08 0.25 026 027 033 -0.13 1.m

POES 0.22 0.14 0.19 0.19 031 u.25 0.02 0.21 I .m

PREI 017 0.03 0 07 0 27 O,lXI 0.21 -0.14 0.05 021 I.00

POSI

-0.17 -0.24 - 0.09 -a23 -0.20 -0.11 0. I I -0.01 - 0.04 1.w

0.06

CLI 0.10 -0.17 -0.22 - 0.09 -Ql3 -0.16 -0.05 0.16 0.1 I -0.16 0.63’ I.W

CL2 - 0.29 -0.21 -0.35 -0.37. - 0.22 -0.25 -0.03 018 0.27 0.23 036’ 0.35’ I.00

THI -0.14 -0.24 -0.46’ -03s -030 -0.36. -0 I3 0.11 008 021 0.69’ 0.50’ 0.60’ I.00

TH2 0 388 0 39’ 001 -007 0.13 0.07 0.11 -0.04 0.23 003 - 0.02 - 0.02 0.11 Oli l.OU

GSPR 0.18 0.23 0.27 a.14 0.26 0.23 0.43’ -015 0.00 -009 005 0.10 0.08 0.05 0.01 l.W

GSPO 0 28 033 0. I 3 -003 0.23 0.21 - 0.06 0.21 0.34 - 0.05 0.02 0.03 0.10 0.23 0 67’ 006 I .oo

CIPR 0.12 -007 - 0.09 0.08 -033 - 0.22 0.458 -0.32 0.00 004 -0.17 -0.21 0.07 -0.19 0.12 0.45: - 0.07 I 00

GIPO -0.37’ -0.30 -0.13 - 0.07 -0 45’ -0.31 -0.27 0.06 011 0.17 0.16 0 26 025 0.14 0.25 - 0.03 0.13 -1339’ I .m

BVAL

KEY FSSI = Fear Survey Schedule, pre-therapy. FSS2 = Fear Survey Schedule, post-therapy. IPA = IPAT, pre-therapy. IPB = IPAT, post-therapy. RSI = Repression-Sensitization Scale, pre-therapy. RS2 = Repression--~nsitization Scale, post-therapy. PRES = Heart rate, phobic slide, pre-therapy. POES = Heart rate, phobic slide, post-therapy. PREI = Heart rate, phobic image, pre-therapy. POSI = Heart rate, phobic image, post-therapy. CL1 = Client’s rating, fear reduction within session. CL2 = Client’s rating. fear reduction outside therapy. THI = Therapist’s rating fear reduction within session. TH2 = Therapist’s rating fear reduction outside therapy. GSPR = GSR, phobic slide, pre-therapy. GSPO = GSR, phobic slide, post-therapy. GIPR = GSR, phobic image, pre-therapy. GIPO = GSR, phobic image, post-therapy. BVAL = B value of regression line for Tone habituation.

* p < 0.05

FSSI FSSZ IPA IPB RSI RS2 PRES POES PREI POSI CLI CL2 THI TH2 GSPR GSPO GIPR GIPO BVAL

FSSI

Table 4. Sorrel&ion among major measures

M

30

KJELL ERIK RUDESTAM and RICHARD BEDROSIAN

was certainly true in this case that the most anxious Ss were the specific phobics. who were subsequently the most successfully treated on this measure of outcome. In any repeated exposure of phobic stimuli, an important determinant of treatment success seems to be the length of time for presenting and imagining the fear cues (c.f. Gelder ef al., 1973). Hekmat (1973) tried an 8-set exposure and found desensitization superior to flooding; yet Sue (1975) concluded that with 30 set of exposure to a stimulus flooding becomes as effective as systematic desensitization. In the present study. Ss were given fear cues for 30 set each and at the end of treatment appeared to have habituated on GSR and heart rate more than Ss receiving desensitization. Inspection of the self-report mode of measuring change indicates that systematic desensitization is significantly better than flooding and especially so for specific phobics. This finding is consistent with investigators such as Boulougouris er al. (1971) and Gelder and Marks (1966) and suggests that Ss prefer to be treated with desensitization, that they see themselves as more improved with it. and that their therapists independently agree. In fact, although physiological and self-report measures did not lead to similar conclusions, correlations were high within these response modalities. Unlike selfreport estimates of success, objective tests of anxiety indicated significantly more change for social phobics. This is not an entirely surprising result, since anxiety measures such as the RS, IPAT, and FSS tap various fears that are not necessarily characteristic of Ss with focused phobias. Finally, some indication of convergent validity for this particular interaction of type of phobia, treatment method, and therapy outcome derives from the relatively high correlations between measures within a given response modality: REFERENCES BOUDEWYNS P. A. and WILSON A. E. (1972) Implosive therapy and desensitization therapy using free association in the treatment of in-patients. J. ahnorm. Ps~‘chol. 39(l). 123-132. BO~‘LOUGOURISH. C.. MARKS I. M. and MARSET P. (1971) Superiority of flooding (implosion) to desensitization for reducing pathological fear. Behac. Rrs. trnd ‘Fherup! 9, 7-14. CORNISH R. D. and DILLEY J. S. (1973) Comparison of three methods of reducing test anxiety: systematic desensitization. implosive therapy, and study counseling. J. counselling PsychoI. ZO(6). 499-503. DENNY M. R. (1975) Critical aspects and implications of relief and relaxation. Invited address at Association for Advancement of Behavibr Therapy Meetings, San Francisco. California. GELDER M. G.. BANCROFT J. H. H.. GATH D. H.. JOHNSON D. W.. MATHEWS A. M. and SHAW P. M. (1973) Specific and non-specific factors in behavior therapy. Br. J. Psrchiar. 123, 445462. GELDER M. G. and MARKS I. M. (1966) Severe agoraphobia: A controlled prospective trial of behaviour therapy. Br. J. Psych& 112, 309-319. HEKMAT H. (1973) Systematic vs sematic desensitization and implosive therapy: A comparative study. J. cotlsult. c/in. Psychol. 40, 202-209. KLORMAN R.. WIENSENFELD A. R. and AUSTIN M. L. (1974) Autonomic responses to affective visual stimuli. Psychophysiology 12. 553-560. LADER M. H.. GELDER M. G. and MARKS I. M. (1967) Palmar skin conductance measures as predictors of response to desensitization. Psychosom Res. 11, 283-290. LADER M. H. and MATHEWS A. M. (1968) A physiological model of phobic anxiety and desensitization. Behar. Rex and Therap! 6, 411421. LALXR M. H. and WING L. (1966) Physiological Measure& Sedaticr Drugs. crud hforhid Answry. Maudsley Monograph No. 14. Oxford University Press. London. LAY<; P. .I. (1971) The application of psychophysiological methods to the study of psychotherapy and behavior modification. In: Hundhook oj’Ps!,chorherupy and Beharior Chaugr (Eds A. E. BERGIN and S. L. GARFIELD). Wiley. New York. LEITENBERG H.. AGRAS S.. BUTZ R. and WINCZE J. (1971) Relationship between heart rate and behavior change during the treatment of phobias. J. ahnorm. Psycho/. 78, 59-68. MARKS 1. M.. BO~LOUG~URIS J. C. and MARSET P. (1971) Flooding vs desensitization in the treatment of phobic patients: A cross-over study. Br. J. Psychiat. 119, 353-375. MATHEWS A. M. (1971) Psychophysiological approaches to the investigation of desensitization and related procedures. Psycho/. Bull. 76, 73-91. M~ALI~A W. L. and NAWAS M. N. (1971) The comparative effectiveness of systematic desensitization and implosive therapy in the treatment of snake phobia. J. Brhur. Therap>~ rzp. Psych&. 2, X5-94. RA(.HMA~*:S. (1966) Studies in desensitization-Ii: Flooding. Behur. RLKV.und Thrrupy 4. l-6. SUF D. (1975) The etTect of duration of exposure on systematic desensitization and extinction. Behoc. Rex and Therapy

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