Behav. Res. k Therapy, 1973, Vol. I I. pp. 303 to 312. Pergamon Press. Printed in England

FREQUENCY AND DURATION OF HIERARCHY ITEM EXPOSURE IN A SYSTEMATIC

DESENSITIZATION ANALOGUE*

STEVEN M. Ross? and STEWART PROCTOR

Department of Psychology, University of Utah, Salt Lake City, Utah, U.S.A.

(Received 2 1 September 1972)

Summary-Little is known regarding the importance of stimulus presentation variables in desensitization. A repeated measures factorial research design was utilized lo investigate the role of hierarchy item frequency and duration in a desensitization analogue. Two frequency levels (1 and 3) and three total duration levels (3 ,12 and 30 set) were combined to form six treatment groups; an additional no-treatment control group was also used. Results in both overt behavioral and subjective fear response modes suggest that single exposures are preferable, but that this preference is localized primarily in the longer total duration range. Long single exposures to hierarchy items yielded the greatest and most persistent changes in both response modes. It is suggested that clinicians utilize item presentations of this sort to determine their efficacy in actuat therapy conditions. Choice of technique for assessing change and the utility of analogue studies are also briefly discussed.

THERE remains little doubt that systematic desensitization (SD) can be a highly effective means of attenuating avoidance and fear reactions. An abundance of clinical and laboratory evidence to this effect has now been accumulated (Bandura, 1969; Paul, 1969a, b). More

recently, researchers have turned from the question of whether SD works to questions of how, why, and under what conditions it works. It was Breger and McGaugh (1965) who

first admonished behavior therapists to be aware that a treatment’s effectiveness is not necessarily proof of the theory proposed to explain it. Considerable controversy has evolved regarding the mechanisms underlying desensitization (e.g. Lang, 1969; Locke, 1971; Wilkins, 1971, 1972; Wilson and Davison, 1971), and it is clear that the issue is far from settled. The possibility that a variety of mechanisms operate concurrently to produce the net therapeutic effect must be accepted, and only concerted research efforts representing a number of theoretical perspectives will shed further light on the matter.

Within the original theoretical context proposed by Wolpe (1958), a number of potentially relevant treatment parameters have still not been systematically explored. Paul (1969b) noted some years ago that there was considerable variation in the SD techniques used in controlled laboratory analogues, let alone the variety characteristic of the clinical literature. While much attention is currently being given to alternative approaches such as expectancy of therapeutic gain (c.f., Oliveau ef al., 1969; Woy and Efran, 1972), the therapist as a social reinforcing agent (cf., Wagner and Cauthen, .I 968), the role of modeling (cf., Bandura and Menlove, 1968), and the reduction of physiological arousal (cf., Lader and Mathews,

l A preliminary portion of this paper was read at the annual meeting of the Western Psychological Association, Los Angeles. 1970. A grant from the University Research Committee, University of Utah, made this study possible.

t The data represent a portion of the first author’s doctoral dissertation completed under the directionof the second author at the University of Utah, 1970. First author’s current address: Psychology Services, Veterans Administration Hospital, Salt Lake City, Utah, U.S.A. 84113.

303

304 STEVEN M. ROSS and STEWART PROCTOR

1968; van Egeren, 1971) there remains a host of questions pertaining to the results of the SD procedure itself. Notably deficient is our understanding of stimulus presentation vari- ables within the Wolpean SD paradigm, It is suggested that the continuation of parametric studies of the SD paradigm is, for pragmatic reasons alone, a worthwhile enterprise. Additionally, such research may contribute to the fund of knowledge requisite to under- standing the mechanisms responsible for the considerable success SD has attained as a therapeutic method.

Stimulus presentation parameters in systematic desensitization Initial instruction on the details of conducting SD was ambiguous. Wolpe (1958) orig-

inally recommended that hierarchy item duration vary, using short initial exposures of about 3 set and subsequent longer exposures up to approximately 10 sec. However, he had little to say with regard to frequency of repetition of items. Wolpe and Lazarus (1966) later use exposure durations down to one or two set in certain circumstances. Most recently, Wolpe (1969) has recommended a relatively fixed duration of 5-7 set with repeated exposures, but the actual frequency of exposure to any given item is dependent upon subjective reports of anxiety reduction. Paul (1969b) summarizes the available evidence on temporal variation in laboratory research analogues of SD and concludes that at least four distinct variations of the treatment have been employed. His review reiterates the need for systematic explora- tion of temporal parameters in SD.

A study by Proctor (1969) suggested that, with regard to overt avoidance behavior, longer exposure durations to hierarchy items (with frequency of presentations held constant) yielded the greatest amount of change, while self-report of fear reduction was significantly related to an interaction between exposure length and the type of pretreatment training Ss were given. More specifically, Ss given relaxationtraining showed greater self-reported fear reduction when shown items for a shorter duration (5 set vs. 20 set), while Ss not trained in relaxation showed an extinction-like effect seen in overt avoidance behavior: the longer the exposure time, the more change occurred. Lang, Melamed and Hart (1970) noted that briefer repetitions of items led to significant decreases in both physiological arousal and self-report of fear, although the effect on overt avoidance behavior was not included in their study. Taken together, the Proctor (1969) and Lang, Melamed and Hart (1970) studies suggest differential effects upon the overt behavioral and subjective self-report response systems, an outcome which has been noted before (Lang, 1969; Bandura, 1969) in behavior modification studies in which more than one measure has been taken.

The Proctor (1969) study simply compared short (5 set) vs. long (20 set) exposure to items without controlling for total duration of exposure. The purpose of the present study is to more carefully examine the temporal parameters of item presentation in the desensiti- zation paradigm. Specifically, a factorial design is employed in which duration of exposure can be varied along with frequency (single vs. multiple exposures), thereby allowing com- parisons of item duration effects apart from total duration of exposure. It was hypothesized that: (1) longer the total exposure duration of each item, the greater the reduction in overt avoidance behavior; (2) for equivalent total durations, single exposures would be more effective in reducing overt avoidance behavior than shorter multiple exposures; (3) with regard to verbal reports of anxiety level, greater reductions would be obtained with shorter total duration of exposure; furthermore, (4) multiple presentations will be more effective in reducing verbal reports of anxiety than single exposures when total duration is held constant.

FREQUENCY AND DURATION OF HIERARCHY ITEM EXPOSURE 305

Frequency of exposures

r

Totol duration of exposures

3 set 12 set 30 set

One 3 set One 12 set One 30 set exposure exposure exposure

No treatment

Three I set Three 4 set Three IO set

exposures exposures exposures

FIG. 1. Summary of experimental design.

Research design In order to test these hypotheses, a 2 x 2 x 3 repeated measure factorial design with an

additional untreated control group was employed as summarized in Fig. 1. The independent variables were frequency of exposure to each item (one or three) and total duration of exposure to each item (3, 12 or 30 set). Pretest, post-test, and follow-up assessments con- stituted the repeated measure component. Since the major focus of the experiment was on the stimulus presentation parameters rather than the well-established effectiveness of SD, no pseudotreatment group was included in the design. Avoidance test scores and subjective reports of anxiety during the avoidance test were the primary dependent measures.

METHOD

Subjects A survey check list containing seven commonly feared and readily photographed stimuli

(sharp knives, mice, worms, cats, dogs, rats, and harmless snakes) was administered to over 1200 undergraduate students in psychology classes at a large state university. The 389 students indicating both ‘much’ or ‘very much’ disturbance in the presence of a harmless snake and a willingness to participate in the research were contacted by telephone for a combination screening session and pretreatment avoidance test (AT). Those who progressed more than half way in the IO-step AT were eliminated from the subject pool in order to obtain maximally avoidant subjects. The final subject pool contained 70 females and 7 males, all of whom were randonmly assigned to one of seven groups with the limitation that males were equally distributed across groups.

Apparatus Separate rooms were used for ATs and SD. The ATs were conducted by one of two

experimentally naive assistants with the help of prerecorded instructions. If completed, the taped instructions requested S to approach a terrarium containing a 2-foot Garter Snake (Thamnophis elegans), remove the cover, don gloves, touch the snake with one finger, and then pick it up. Subjects were informed that the snake was harmless. Approach was measured in 2-ft intervals by means of numbered marks on the floor. Snake activity level (SAL) was recorded by the assistant at each step in the AT on a scale from 1 to 4 depending upon the degree of movement.

A treatment room with an adjoining control room had a 16 x 22 in. opaque glass screen fitted in a section of the wall common to both of them. The control room was furnished with a slide projector, tape recorder, and two signal lights. The treatment room contained two

306 STEVEN M. ROSS and STEWART PROCTOR

reclining chairs separated by a partition and two sets of headphones. Microswitches on the arms of the chairs enabled each S to activate one of the two signal lights in the control room. The slides which constituted the treatment hierarchy were back-projected on the screen from the control room while Ss listened to the taped SD procedure through the head- phones,

A standardized hierarchy of items to be used with all Ss was developed by means of a Q-sort technique employing an independent sample of 18 snake-avoidant Ss. This technique (described in detail by Ross, 1970) affords the advantages of assuring a common therapy experience for all Ss while at the same time providing a sound psychometric rationale for the position of items in the hierarchy. Starting with a sample of 35 pictures involving one. two, or three snakes photographed from a variety of distances and degree of enclosure, and occasionally including human interaction, the hierarchy which was developed eventually included 12 items rated across a range from minimally to maximally fear-eliciting. Items were selected on the basis of both their mean ordinal position and their standard deviations such that the 12 items were equally spaced and showed minimal variation around their means. The ordering of the 12 final items was highly reliable (mean interrater reliability = 0.82; test-retest reliability = 0.98).

Procedure Subjects were asked to verbally report a subjective fear (SF) score similar to Wolpe’s

subjective units of disturbance (SUDS) rating (1958; 1969) at each point they reached in the AT. Once assigned to groups, Ss in the six treatment groups were taught how to relax themselves via a taped training procedure (after Paul, 1966; Proctor, 1968). All of the first and half of the second session were devoted to relaxation training. In addition, Ss were asked to practice twice daily between sessions.

Beginning with the second session, Ss were asked to signal if they did not feel deeply relaxed after going through the relaxation procedure and were told to try to maintain the maximum degree of relaxation while viewing items. Prior to presentation, a brief description of each hierarchy item was given. The item was then shown on the screen for the pre- determined duration. The Ss saw items 1-3 during the second session. Each remaining session began with a truncated version of relaxation training instructions. During Session 3, items 3-6 were presented; items 6-9 were presented during Session 4, and items 9-12 during Session 5. Intervals between items remained constant at 45 set for all treatment groups. During this interval, Ss were asked to signal if they felt anxious while viewing the item and were given standard instructions to continue relaxing (after Paul, 1966). Items were shown for the predetermined durations and number of presentations regardless of any signaling that occurred. Item and instruction presentations were entirely automated.

Subjects who had been randomly assigned to the untreated control group were given a second AT 3 weeks after the first AT (to correspond to the interval at which treated Ss received their second AT) and a third AT from 4 to 6 weeks after the second AT (to corre- spond to the follow-up period for treated Ss).

RESULTS

Snake activity level (SAL) The two assistants administering the ATs had participated simultaneously in 20 pre-

experimental observation trials (no S present) during which they rated snake activity level

FREQUENCY AND DURATION OF HIERARCHY ITEM EXPOSURE 307

(SAL). The rating of SAL proved to be highly reliable between raters (mean Spearman rho = 0.89). However, the subsequent overall correlations between SAL and the two dependent variables at both post-test and follow-up proved to be negligible and unsyste- matic (-0.23 to 0.05); hence, statistical control for SAL in the analyses of the dependent variables was not necessary.

Dependent measure analyses Studies of therapy effectiveness have often employed change or difference scores in

assessing outcome (e.g. Lang and Lazovik, 1963). While the change score has intuitive appeal to the clinician, it is unfortunately fraught with serious psychometric limitations (cf., Bereiter, 1963). Following the rationale provided by Feldt (1958) and Cronbach and Furby (1970), analyses of variance (ANOVAs) with repeated measures were employed as the primary method of assessing the outcome. For comparative purposes, other methods were also used (analyses of change scores and analyses of covariance using prescores as the covariate), but only the ANOVAs and related statistics are reported here. Alternative methods of analysis provided no substantial differences in the pattern of results and hence would be largely redundant.*

Avoidance test (AT) scores An overall reduction in AT scores among-the six treatment groups is reflected in a sig-

nificant repeated measures ANOVA main effect for Stage (pretest, post-test, and follow-up). Furthermore, a simple unequal n t-test revealed that the six treatment groups combined were significantly less avoidant than the control group at post-test (t = 3.05, df = 75, p < 0.01). At follow-up, the six treatment groups combined were no longer significantly less

6

t

c---c Single exposure '\ _--- --o

l - Triole emoswe b_---

21 I I Pretreotmcnt Posttreatment Follow-up

stage

FIG. 2. Mean avoidance test (AT) scores at pretest, post-test, and follow-up showing the effect of exposure frequency. Higher scores indicate greater avoidance.

avoidant than the control group (p>O.lO), although comparisons of individual pairs of groups, to be discussed below, did yield significant follow-up differences between certain treatment groups and the control group.

As noted earlier, however, the major intent of the present paper was not to test the already well-documented efficacy if SD per se; more pertinent to its purpose are the data demonstrating the impact of variation along theitem frequency and duration dimensions.

l Raw data and summaries of the various types of analyses are available from the authors upon request.

308 STEVEN hf. ROSS and STEWART PROCTOR

The ANOVA of AT scores yielded a significant Frequency x Stage interaction (F = 3.73, df = 2/120, p < 0.05) which is visually portrayed in Fig. 2. As can be seen, the combined single exposure groups showed greater reductions in avoidance behavior than the combined triple exposure groups. However, the repeated measures ANOVA also produced a sig- nificant Duration x Frequency x Stage interaction (F = 2.61, df = 4/120, p<O.O5), the

post-test aspect of which is visually summarized in Fig. 3. * The figure clearly suggests that

single exposures of long duration are most preferable in reducing overt avoidance behavior. Using a Dunnett r-test procedure for comparing all possible pairs of means, the average AT score for the 30 set single exposure group was significantly less avoidant at post-test than either the control group or any other single treatment group (p < 0.05). Also, while every treatment group was less avoidant than the control group at post-test, only the 12 set and 30 set single exposure groups remained significantly less avoidant than the control group at follow-up (p < 0.05). Hence, it is reasonable that the implications of the Frequency x Stage

6

5 t

1 L o----o Single exposure

l - Triple exposure

0 I I I 3 12 30

Totol duration. set

FIG. 3. Mean avoidance test (AT) scores at post-test showing the interaction of exposure frequency and duration. Higher scores indicate greater avoidance.

interaction (which suggests a preference for use of single exposures) should be modified; single exposures of longer duration appear to actually account for the single exposure preference. When using short exposure times (e.g. 3 set), single or multiple exposure frequency would appear to be inconsequential. Only at the 12 set and particularly the 30 set durations did the single exposure preference emerge; furthermore, only the 12 and 30 set single exposure groups remained significantly less avoidant than the control group at follow-up.

The general attenuation of AT effects at follow-up has been noted in other studies focusing primarily on SD effectiveness; as in these studies, the spontaneous improvement of the un- treated control group (see Fig. 2) clearly plays a role in the attenuation phenomenon.

Subjective fear (SF) scores As was obtained with the AT scores, a repeated measures ANOVA of the SF raw scores

of the six treatment groups yielded a significant main effect for Stage (F = 54.96, df = 2/120, p < 0.001) which reflects an overall reduction in SF scores across the three testing occasions. Moreover, the six treatment groups combined yielded significantly lower SF

l The highly similar, and hence redundant, interaction pattern at follow-up is not presented here in the interest of conserving space.

FREQUENCY AND DURATION OF HlERARCHY ITEM EXPOSURE 309

scores when compared with the control group at both post-test (t = 3.87, df = 75, p -C 0.001) and follow-up (t = 2.28, df = 75, p < 0.05). As with the AT data, the implication of these data is that some form of SD is preferable to no treatment; furthermore, the effect would appear to be generally more durable since the comparison of all treatment groups with the control group remained significant at follow-up for the SF data whereas it did not with the AT data.

In terms of the major interest of the present study, the repeated measures ANOVA revealed a significant Frequency x Stage interaction (F = 3.63, df = 2/120, ~~0.05) the post-test aspect of which is presented in Fig. 4. As with the AT data, there is an obvious

70

60

E :: 50

% 40

6

s 30

20 0---o Single exposure

l - Triple exposure

IO I I Pretreatment Posttreotment Follow-up

Stope

FIG. 4. Mean subjective fear (SF) scores at pm-test, post-test, and follow-up showing the effect of exposure frequency. Higher scores indicate greater subjective fear.

preference revealed for the use of single exposures over triple exposures of equivalent total durations. While the SF data did not yield the significant three-way Frequency x Duration x Stage interaction obtained in the AT analysis, Fig. 5 demonstrates that a similar pattern was obtained. Dunnett r-test comparisons of all possible pairs of means revealed that, while all treatment groups differed significantly from the control group at post-test, only the 30 set single exposure group remained so at follow-up (p -C 0.05). Figure 5 clearly reveals that

70

t

---_--____--___-_----

60

Y t-

5 50 t-

% 40

c x

= 30 1

I- --- Control 20 cb -a Single erposures

.- Triple exposures -\

. . IO 1

3 I2 30

Total duration. set

FIG. 5. Mean subjective fear (SF) scores showing the interaction of exposure frequency and duration. Higher scores indicate greater subjective fear.

310 STEVEN M. ROSS and STEWART PROCTOR

the 12 and 30 set single exposure groups have the lowest mean SF scores at post-test as well. Hence it is reasonable to conclude that the preference for single exposures in reducing self- reported anxiety levels is again largely localized in the longer duration range. As with the AT data, Fig. 4 suggests that the attenuation of effects at post-test is at least partly due to a reduced mean SF score for the control group.

In general, the results of the self-report data are analogous to the data obtained in the avoidance behavior mode. Hence, the original hypothesis which predicted that shorter total durations would achieve the greatest reduction in self-reports of anxiety was not substantiated. Contrary to expectations, single exposures proved generally preferable to multiple exposures of equivalent total durations. Furthermore, the single exposure effect appears to be localized in the longest total durations, although the most critical interaction which would verify this outcome did not obtain. Thus single long exposures to hierarchy items appear to be the method of choice with regard to either the overt avoidance behavior mode or the subjective self-report mode.

DISCUSSION

The results of this study suggest that, in general, single exposures to hierarchy items are preferable to shorter multiple exposures of an equivalent duration in reducing both overt avoidance behavior and subjective reports of anxiety level. However, by controlling both total duration and frequency of exposures, the study also revealed that the single exposure preference is primarily localized in the longer duration range. These results confirm Proctor’s (1969) finding with regard to overt avoidance behavior in which it was shown that 20 set single exposures were preferable to 5 set single exposures. The present study suggests that the preference for longer exposures can only be expected under single (as opposed to multiple fractionated) exposure conditions. The fact that single long exposures accounted for the greatest reduction in both dependent variables might be construed as supporting an in- hibition mode1 of extinction (see Kimble, 1961) since shorter multiple exposures (analogous to spaced trials) are not as effective as single trials of equivalent total duration (analogous to massed trials). While Wolpe’s original reciprocal inhibition mode1 (1958) does not seem to be particularly applicable in explaining these data, it is interesting to note that his more recent procedural variations (Wolpe, 1969) incorporate multiple repetitions of fixed dura- tions, a format which more clearly approximates an extinction paradigm.

The attenuations of therapeutic effects at follow-up is consistent with other research (e.g. Lang and Lazovik, 1963; Proctor, 1969) and, as was noted earlier, appears to be due at least partially to the improvement of the control group across the three testing occasions. In a related point, Agras (1967) has noted that generalization and maintenance of treatment gains may depend in part upon extra-therapeutic experiences with the feared object. In the present experiment, Ss were asked, following the last testing occurrence, whether or not they had had any direct or indirect contacts with a snake (harmless or otherwise) during the experimental period. Seven of the 11 control Ss (64%) stated that they had had at least indirect contact (e.g. seeing a snake on television, reading something about snakes, etc.); similarly, a full 74 % of the treatment Ss reported at least indirect contact. These results are high in comparison with data reported by Bandura, Blanchard and Ritter (1969) in which 47% of all Ss reported vicarious encounters of some sort during treatment.

With regard to subjective reports of anxiety, the data in the present study were largely contrary to the hypothesized outcomes. Rather than yielding a preference for short total

FREQUENCY AND DURATION OF HIERARCHY ITEM EXPOSURE 311

durations and for multiple exposures within various total durations, the self-report data actually paralleled the AT data: single exposures were generally preferable to multiple exposures, particularly at post-test, and Fi g. 5 suggests the same type of Duration x Fre- quency interaction found in the AT data. Although the interaction failed to achieve statistical significance, it would appear that single long exposures or hierarchy items are still pre- ferable to multiple exposures of any duration. The fact that the SF data are contrary to expectations based on prior research reiterates the often-noted fickle and sensitive relation- ship between the overt behavioral and subjective verbal response modes. In the present study, the pretreatment correlations for all Ss between the two measures was 0.29 which is nearly identical to Proctor’s (1969) earlier report of a 0.27 correlation. However, the correlation between the two measures increased to 0.41 at post-test and to 0.45 at follow-up, corresponding to values of 0.55 and 0.57 obtained by Proctor (1969) using somewhat different data (correlations of indices of change rather than raw scores). It should be noted that there were marked procedural differences in obtaining the SF data between the earlier Proctor (1969) study and the present one, and hence little can be offered in the form of clarifying the natures of the relationship between overt behavioral and verbal self-report data modes. Nonetheless, it is clear that data from one mode are not a very reliable predictor of performance in the other mode; subtle procedural differences undoubtedly play a significant role in determining the extent to which the two measures covary.

In terms of the clinical implications of these data, it must be pointed out that the present study is admittedly offered as an analogue of the genuine clinical situation. The Ss parti- cipating in this study were obviously not extremely phobic. In fact, it is highly unlikely that sufficient numbers of extremely phobic persons could ever be obtained to conduct factorial design research since such persons would almost certainly shun participation. On the other hand, if one accepts the behaviorists’ thesis that phobias are basically the extreme range of an avoidance behavior continuum, then the performance of Ss such as those participating in the present study should have direct implications for clinical practice. Ultimately, the ques- tion of applicability of analogue studies to the clinical situations remains an empirical question urgently in need of testing.

In summary, it is suggested that clinicians attempt single long exposure item presentations in SD to determine empirically whether such a procedure is, in fact, superior to the tradi- tional short-to-long exposure method. Such a technique might be viewed as a procedural compromise between the gradual approach originally developed from Wolpe’s (1958) reciprocal inhibition model and the much more dramatic implosive procedures developed by Stampfl (Stampfl and Levis, 1967) which are presumed to be founded upon an extinction paradigm

REFERENCES

AGRAS W. S. (1967) Transfer during systematic desensitization therapy. &hat.. Res. & Therap). 5, 193-199 BASDLIRA A. (1969) Principles of Bd~auior Modificafion. Holt, Rinehart & Winston, New York. BANDURA A., BLANCHARD E. B. and RITTER B. (1969) Relative efficacy of desensitization and modeling

approaches for inducing behavioral, affective, and attitudinal changes. J. pers. sot. Psychol. 13, 173-199. BASDURA A. and MENLOVE F. L. (1968) Factors determining vicarious extinction of avoidance behavior

through symbolic modeling. J. prrs. sot. Psychol. 8, 99-108. BEREITFR C. (1963) Some persisting dilemmas in the measurement of change. In Problem in A4eeasrrring

Change (Ed. C. W. Harris). University of Wisconsin Press, Madison, Wisconsin. BR~CER L. and MCGAUGH U. L. (1965) A critique and reformulation of “learning theory” approaches to

psychotherapy and neurosis. Psychol. Bull. 63, 338-358. CROSBACH L. J. and FURBY L. (1970) How we measure “change”-or should we? PsJchol. Bull. 74, 68-80.

312 STEVEN M. ROSS and STEWART PROCTOR

FELDT L. S. (1958) A comparison of the precision of three experimental designs employing a concomitant variable. Psychometriko 23, 335-353.

KIMBLE G. A. (1961) Hilgordand Marquis’ Condiirioning andlearning. Appleton-Century-Crofts, New York. LADER M. H. and MATHEWS A. M. (1968) A physiological model of phobic anxiety and desensitization.

Behov. Res. & Therapy 6, 411421. LANG P. J. (1969) The mechanisms of desensitization and the laboratory study of human fear. In Behmior

Therap),: Appraisal and Status (Ed. C. M. Franks), pp. 160-191. McGraw-Hill, New York. LANG P. I. and LAZOV~K A. D. (1963) Experimental desensitization of a phobia. J. obnornl. Sot. Psycho!.

66, 519-525. LANG P. J., MELAMED B. G. and HART J. (1970) A psychophysiological analysis of fear modification using an

automated desensitization procedure. J. obnorm. Psycho/. 76, 220-234. LOCKE E. A. (1971) Is “behavior therapy” behavioristic? (Ananalysis of Wolpe’spsychotherapeuticmethods.)

Psychol. Birll. 76, 318-327. OLIVEAU D. C.. AGRA~ S., LEITENBERG H., MOORE R. C. and WRIGHTD. E.(l969)Systematicdesensitization,

therapeutically oriented instructions, and selective positive reinforcement. Behov. Res. & Theropy 7, 27-33.

PAUL G. L. (1966) Insigh! vs. Desensitization in Psychofheropy: An Experimenr in Anxiety Reduction. Stanford University Press, Stanford, California.

PAUL G. L. (1969a) Outcome of systematic desensitization I: Background, procedures, and uncontrolled reports of individual treatment. In Behavior Theropy: Appraisal and Sfotus (Ed. C. M. Franks), pp. 63- 104. McGraw-Hill, New York.

PAUL. G. L. (1969b) Outcome of systematic desensitization II: Controlled investigations of individual treatment, technique variations, and current status. In Behorior Therapy: Appraisal and Status (Ed. C. M. Franks). pp. 105-159. McGraw-Hill. New York.

PROCTOR S. (1968j.The role of duration of exposure to items and pretreatment training in a systematic desensitization analog. Unpublished doctoral dissertation, Indiana University, Indiana, U.S.A.

PROCTOR S. (1969) Duration of exposure to items and pretreatment training as factors in systematic de- sensitization therapy. In Aduonces in Behavior Therapy, 1968 (Eds. R. D. Rubin and C. M. Franks), pp. 105-l 16. Academic Press, New York.

Ross S. M. (1970) The role of duration and number of exposures of hierarchy items in a systematic de- sensitization analog. Unpublished doctoral dissertation, University of Utah, U.S.A.

STAMPFL T. G. and LEVIS D. J. (1967) Essentials of implosive therapy: A learning-theory-based psycho- dynamic behavioral therapy. J. obnorm. Psychol. 73, 496-503.

VAN EGEREN L. F. (1971) Psychophysiological aspects of systematic desensitization: Some outstanding issues. Behov. Res. & Therapy 9, 65-77.

WAGNER M. K. and CAUTHEN N. R. (1968) A comparison of reciprocal inhibition and operant conditioning in the systematic desensitization of a fear of snakes. Behov. Res. & Therapy 6, 225-227.

WILKINS W. (1971) Desensitization: Social and cognitive factors underlying the effectiveness of Wolpe’s procedure. Psychol. Bull. 76, 31 l-317.

WILKINS W. (1972) Desensitization: Getting it together with Davison and Wilson. Psycho/. Bull. 78, 32-36. WUON G. T. and DAVMN G. C. (1971) Processes of fear reduction in systematic desensitization: Animal

studies. PsychoI. Bull. 76, l-14. WOLPE J. (1958) Psychotherapy by Reciprocal Inhibition. Stanford University Press, Stanford, California. WOLPE J. (1969) The Practice of Behavior Therapy. Pergamon Press, New York. WOLPE J. and LAZARUS A. A. (1966) Behovior Therapy Techniques. Pergamon Press, New York. WOY J. R. and EFRAN J. S. (1972) Systematic desensitization and expectancy in the treatment of speaking

anxiety. Behov. kes. & Therapy 10, 43-49.