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Behav. Res. Ther. Vol. 33, No. 5, pp. 579--583, 1995 Copyright ~) 1995 Elsevier Science Ltd

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Worry and the incubation of intrusive images following stress

A D R I A N W E L L S ' a n d C O S T A S P A P A G E O R G I O U 2

tDepartment of Psychiatry, University of Oxford, Warneford Hospital, Oxford OX3 7JX, England and 2Department of Clinical Psychology, University of Liverpool, Liverpool L69 3BX, England

(Received 1 June 1994)

Summary--This study investigated the effects of post-event processing on intrusive images following exposure to stress. It was hypothesized that ruminative activity, especially verbal worry about a stressor leads to an incubation of intrusions. Five groups which differed in the use of post-event processing strategies were used to test for a hypothesized co-joint mechanism underlying the effect. Worrying about a stressor for a period of 4 min after exposure led to significantly more intrusions in the next 3 days than a settle-down control condition. The strategies of imaging about the stressor, distraction, and worrying about usual concerns, produced a significant incremental linear pattern of intrusions across these groups. The pattern of results was as predicted by a co-joint model in which incubation results from 'tagging' of memories and blocked emotional processing. The clinical implications of these findings are briefly discussed.

Several cognitive theories have recently been advanced to account for the function of worry. Borkovec and lnz (1990) suggest that worry in generalized anxiety disorder may serve to avoid unwanted somatic-affective responses which are associated with other forms of thought, namely images. More specifically, the predominantly verbal activity of worry may be employed to distract from more distressing types of thought. If this is correct the cessation of worry could have aversive consequences in the form of intensified negative affect, thus worry may be negatively reinforced in a way that could lead to a 'loss of control' over the activity.

In contrast with this theory, Tallis and Eysenck (cited in Eysenck, 1992) propose that worry may serve to orient the cognitive system to threat rather than away from 'emotional" threat. In this context worry has been viewed as serving an alarm, prompt and preparation function. Worry is more likely to be triggered when the perception of threat is high. The threat level is determined by an interaction between the subjective probability of an event occurring, the imminence, perceived aversiveness and the perceived ability to cope.

Whilst these approaches offer an account of the potential significance of worry, they do not locate worry within a detailed information processing framework. Such a framework might be useful for conceptualising in detail the use of worry as a processing strategy, its control, and factors responsible for transforming normal worry into pathological types. In view of this, Wells (1994a, b) has proposed a model in which particular beliefs, cognitive processes and cognitive-regulation strategies are thought to be involved in the selection of worry as a processing strategy, and in the transformation of normal worry into pathological varieties. In this model worry is conceptualized as a cognitive strategy for dealing with threat, the use of this particular strategy is motivated by subjects' meta-cognitive knowledge which directs the conscious controlled processing system to use predominantly verbal and perseverative modes of processing in response to certain stimuli. Worry becomes problematic and subjectively uncontrollable when it is used to distract from emotional processing of other thoughts, when it is consciously monitored by the individual and when it is the target of certain thought control attempts. In this context meta-worry, i.e. worry about worry and concomitant pre-occupation with it becomes a pathologizing element. One of the central predictions of this model is that following exposure to threat, worry may block the effective processing of emotion associated with threat-related thoughts. It will therefore lead to a maintenance of intrusions as a symptom of this incomplete emotional processing (cf. Rachman, 1980). In addition worry about a stressor may lead to a 'tagging' of threat-related material in memory such that retrieval cues for threat-related intrusions generalize, and intrusive thoughts become more frequent. Consistent with the hypothesis that worry increases threat-related intrusions, a pilot study by Butler, Wells and Dewick (1992) demonstrated that a 4-min verbal worry period following exposure to a gruesome film was associated with significantly more intrusive images about the film over the next 3 days compared with Imaging or 'settling down' periods of equivalent duration.

The aim of the present study was to test the hypothesis that verbal worry increases intrusive imagery following exposure to a threatening stimulus (film) and that the mechanisms of a blocking of emotional processing and 'tagging' operate co-jointly in producing this effect. More specifically, verbal worry about the threat should produce significantly more intrusions than imaging the threat since it will produce more tags and also divert attention away from spontaneous images. The processing of images is thought to be important for emotional processing (e.g. Foa & Kozak, 1986). Imaging should, in contrast produce some tagging but facilitate emotional processing. In this study we also included a 'usual-worry' group in which subjects were instructed to worry about the things they usually worried about. It was hypothesized that this group would produce less tagging than the threat-worry group but block emotional processing. It should therefore lead to more intrusions than the control group and imagery group. A distraction condition was also included, this condition utilized a cognitively undemanding task which should allow emotional processing of images but block the activities of the articulatory loop in working memory, thus minimizing tagging by verbal worry. The co-joint model predicts that intrusions will be most frequent in the condition which blocks emotional processing and also produces high tagging (film worry), and also high in the blocked emotional processing condition (usual worry) whilst the conditions which facilitate emotional processing whilst reducing tagging (imagery and distraction) should show fewer intrusions, and least intrusions should be demonstrated in the no-manipulation control condition, in which subjects allow processing to take its usual course. More specifically,

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we should find a significant linear trend in the frequency of intrusive images such that: control < imagery < distraction < usual-worry < film-worry. The experimental conditions selected reflect only the general demands on attention and tagging, specific demands will be dependent on various situational constraints on processing as well. In testing for the predicted linear trend orthogonal polynomial-based contrasts were planned (e.g. Rosenthal & Rosnow, 1991, pp. 474-477). In addition to this analysis we computed multiple group comparisons for the intrusive thought data.

In the study we controlled for several variables which may confound the effect of worry on intrusions. The following variables were assessed with the aim of ensuring that pre-experimental differences did not exist between groups: private self-consciousness, worry proneness, state and trait-anxiety, Imaging proneness, amount of the stressful film stimulus watched, amount of worry and imagery experienced during the stressor, degree of suppression of worry or images during the manipulation periods following the stressor. The stressor selected for the study was a short (8 min) silent colour film depicting the events leading up to and involving a gruesome workshop accident. The film has been shown to reliably induce anxiety in previous studies (Wells, 1991).

METHOD

Subjects

Subjects were recruited from undergraduate and postgraduate university students, trainee nurses and piano makers. Seventy Ss (35 male) participated in the study, their mean age was 28.47 yr (range 18-55).

Procedure

Fourteen Ss were randomly allocated to each of the five experimental groups with the constraint that 7 men and 7 women appeared in each group. The five groups were as follows: Control group (CG); Imagery (IG); Distraction (DG); and Usual-Worry (UW); and film-worry group (FG). Following allocation to group subjects were asked to complete questionnaires assessing dimensions previously found important as predictors of response to threat and worry (e.g. Wells, 1991). We aimed to verify that there were no pre-experimental differences between groups on these dimensions. The following questionnaires were included:

(l) Private self-consciousness subscale (Fenigstein, Schier & Buss, 1975). A measure of tendencies to focus inward on one's thoughts and feelings.

(2) Penn State Worry Questionnaire (Meyer, Miller, Metzger & Borkovec, 1990). A measure of worry proneness. (3) Speilberger State-trait anxiety inventory (Speilberger, Gorsuch, Lushene, Vagg & Jacobs, 1983). A measure of

current anxiety state and anxiety proneness. (4) Verbalizer-Visualization Questionnaire (Richardson, 1977). A measure of the tendency to process information in

a visual sense.

On completion of the above measures Ss were then asked to complete a 0-100 visual analogue (VAS) rating of their current anxiety ranging from '0 = not at all anxious' to 'I00 = extremely anxious; could not be worse'. They were then informed that they would be shown a "short, silent and gruesome film depicting a workshop accident that actually happened". The film lasted about 8 min and has been found to reliably induce anxiety in previous studies (Wells, 1991). After the film the VAS anxiety rating was again administered along with other VAS measures of the following: (1) frequency of verbal worries during the film (ranging from: 0 = 'none of the time' to 100 = 'all of the time'); (2) frequency of images during the film (ranging from: 0 = "none of the time' to 100 = 'all of the time'; (3) the amount of film watched (ranging from: 0 = 'none of it' to 100 = 'all of it').

A 4-min experimental manipulation period followed the film during which subjects engaged in one of the following; worried about the film and its implications in verbal form (FW); imaged about the film and its implications (IG); engaged in a distraction task consisting of letter cancellation with a memory set size of 3 letters (DG); worried about the things they usually worry about (UW); settled down (CG). At the end of this period VAS anxiety ratings were obtained and VAS ratings of: (1) the proportion of time spent worrying; (2) proportion of time spent imaging (both assessed on scales of 0 = 'none of the time' to 100 = 'all of the time'), and (3) the degree to which worries or images were resisted during the manipulation period (0 = 'not at all' to 100 = 'very much so'). All of the subjects in the study were tested in groups of up to 19. Each group was comprised of mixed manipulation instructions presented in written format to individuals. At the end of the experimental session all subjects were given a diary and asked to record the occurrence of intrusive images about the film during the next 3 day period.

RESULTS

One-way analyses of variance showed that there were no significant differences between groups in any of the pre-experimental trait variables, in state-anxiety or pre and post film VAS anxiety ratings. Visual-analogue anxiety ratings differed significantly between groups following the manipulation period (F = 4.57, d.f. = 4, P < 0.003). Scheffe post hoc comparisons (P < 0.01) demonstrated that the usual worry group were significantly more anxious than the control group at this time. No other differences were significant. Descriptive statistics for the pre-experimental and VAS-anxiety measures are displayed in Table 1.

The main analysis of interest for the current hypothesis concerned testing for a linear trend in the intrusive imagery data across groups. The mean number of intrusions for each group are displayed in Fig. I. The overall F-test showed a significant between groups effect ( F = 4 . 1 , d.f. =4 , P <0.005) and a significant linear term ( F = 15.25, d . f .= 1, P <0.0002) as predicted. Scheffe tests showed that the film-worry group reported significantly more intrusions than the control group. The difference between the usual-worry group and the control group just failed to reach significance (P = 0. I). No other differences were significant.

Self-report ratings of the proportion of time spent worrying or imaging during the manipulation period are presented in Table 1. One-way ANOVA showed that there were no significant differences between groups on time spent worrying. However, significant differences did emerge for time spent imaging (F = 5.95, d.f. = 4, P <0.0004). Scbeffe tests demonstrated that the film-worry group reported more time imaging than the control group (P < 0.05), and the imagery

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Table I. Means and SD (in parentheses) for all experimental variables

Film Usual Group Control worry Image Distract worry

ST 31.0 (8.2) 35.0 (8.6) 36.6 (9.9) 35.5 (7.9) 36.1 (7.8) TR 36.6 (8.7) 39.8 (I 3.5) 41.4 (9.0) 41.7 (7.8) 40.4 (8.5) PSWQ 44.3(10.0) 48.1 (11.9) 48.6(11.3) 45.0(13.4) 43.2(10.9) VVQ 8.1 (2.6) 8.1 (2.0) 7.4(I.6) 9.2 (2.7) 9.1 (2.8) PSC 20.1 (6.5) 23.3(5.1) 22.2(5.3) 24.7(7.1) 23.8(5.0) A1 25.0 (25.4) 27.5 (25.7) 46.4 (30.6) 29.5 (23.2) 31.7 (29.8) A2 27.5 (29.9) 43.8 (34.1) 59.1 (28.6) 56.3 (35.1) 51.1 (31.9) A3 14.2(22.0) 27.9(22.1) 40.8(35.1) 45.8(30.1) 56.7(32.2) Film watched 27.8 (32.7) 35.9 (24.9) 45.0 (32.7) 59.6 (42.7) 39.8 (35. I) RESW 21.0 (27.8) 22.2 (27.5) 42.0 (33.8) 29.4 (31.8) 30.9 (39.4) RESI 23.4 (27.9) 38.0 (33.9) 35.4 (28.2) 32.9 (30.6) 34.7 (39.5) INT 1.4 (1.6) 6.9 (3.9) 3.3 (2.6) 3.5 (5.0) 6.6 (6,8) TIMI 22.2 (19.8) 63.7 (29.5) 66.9 (38.3) 32.8 (28.2) 42.9 (29.9) TIMW 23.0(37.3) 33.6(18.0) 35.1(25.4) 23.4(30.5) 21.4(19.1)

Note: ST = State anxiety; TR = Trait-anxiety; PSWQ ~ Penn-State worry; VVQ = Verbalizer- visualizer score; PSC = Private Self-consciousness; AI-A3 = VAS anxiety ratings at times 1-3; Film watched = amount of film watched; RESW = Resistance of worry during manipu- lation period; RESl = Resistance of Imagery during manipulation period; INT = Intrusive images over 3 days; TIMI = Time spent imaging during manipulation period; TIMW = Time spent worrying during manipulation period.

group also reported more time imaging than the control group (P < 0.01). Means and standard deviations for these data are presented in Table I.

Finally we assessed whether there were any differences in the degree to which subjects resisted images or worries during the manipulation period since the suppression of thoughts has been linked to an increase in thought frequency (e.g. Wegner, Schneider, Carter & White, 1987). We also tested for differences in the amount of film watched. N o significant differences emerged for these potential confounding variables.

DISCUSSION

This study tested the hypothesis that verbal ruminative activity, namely worry following exposure to a stressful stimulus is associated with an increase in subsequent intrusive images about the stressor. This incubation effect of worry can be explained in terms of a dual-mechanism model in which the occurrence of tagging and emotional processing operate co-jointly in moderating the frequency of subsequent intrusions. Tagging refers to the linking of other material to the stored representations of the stressor in memory so that an increased range of material serves as a retrieval cue. Tagging requires accessing of representations of the stressor (i.e. thinking about it) plus elaboration of the material stored. Emotional processing refers to the encoding of information in memory which is inconsistent with the existing emotional structure, such as reduced bodily arousal. In order for this to occur the processing of emotional imagery should be facilitated.

The results of the present study clearly support the prediction that verbal worry increases the frequency of subsequent intrusive images. Moreover, the pattern of results is consistent with that expected from the tagging-emotional processing

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model. Worry about the film produced most intrusions, as predicted, since this condition both tags and blocks emotional processing. As expected based on this model, usual worry also produced a high frequency of intrusions. The hypothesized mechanism here is the blocking of the processing of images, since worry is a cognitively demanding and predominantly verbal activity. However, usual-worry should produce relatively few tags. It was predicted that imaging the stressor should be associated with less intrusions than the film-worry condition and this effect was demonstrated. In the case of imaging, emotional processing was theoretically facilitated and tagging reduced in relation to film-worry. However, an interesting finding was that the imagery group reported more intrusions than the control group, although this was not significant. This finding does however, warrant further study because of its potential clinical implications. We presume that this occurred because the imaging condition which instructed subjects to image the events in the film and 'their implications' also stimulated some tagging albeit less than the verbal-conceptual analysis of film-worry. Imaginal exposure has been used as a treatment for intrusions and traumatic memories in post-traumatic stress disorder (e.g. Foa, Rothbaum, Riggs & Murdock, 1991). If imagery work is allowed to produce tagging it may exacerbate intrusions. The effectiveness of this type of imagery procedure may depend on reducing tagging, i.e. it may depend on the reduction of concurrent conceptual and ruminative processing.

Worrying about an external stressor may not be the only pathway to incubation effects. Wells (1994b) and Wells and Matthews (1994) assert that worrying about intrusions themselves may contribute to a perceived loss of control over intrusive thoughts, by lowering thresholds for intrusion of this material and maintaining activation of intrusion related material in memory. Moreover, Wells and Matthews (1994) suggest that post-event processing strategies which allow traumatic material to decay in its own right in consciousness are least problematic and should be encouraged, perseverative and active conscious processing of the stressor or of intrusions is in contrast a dysfunctional strategy. Consistent with this proposition the control group in the present study who were simply informed that they had time to settle down after the film reported least intrusions.

The proportion of time reported worrying during the manipulation periods did not differ significantly across groups. This lack of difference may reflect a failure of the manipulation, however it replicates that found in a previous study by Butler et al. (1992). It is more likely that this result represents the insensitivity of retrospective measurement and problems with the measurement of time spent worrying rather than the assessment of effort invested in worrying. Clearly the manipulations did have an influence since both the film worry group and the imagery group reported significantly more time imaging than the control group. These imagery data are displayed in Fig. 1. The difference in subsequent intrusions cannot be explained solely in terms of differences in imagery during the manipulation period since subjects who worried about the film and those who imaged the film reported similar proportions of imagery but differed significantly in number of subsequent intrusions. This pattern further supports the co-joint incubation model in which film-worry subjects activated internal representations of the stressor (evidenced by higher imagery during the mentation period) and tagged them whilst diverting attention away from images towards verbal-conceptual activity. It is possible that the amount of verbal worry is not the central moderating factor in determining the frequency of subsequent intrusions but the amount of attention devoted to imagery rather than worry may be the determining factor. The occurrence of imaginal intrusions appears to be a normal consequence of exposure to this type of stressor, and this may be part of an inbuilt emotional self-regulation strategy. However, the effectiveness of the strategy may be disrupted by the use of particular attentional styles.

In conclusion, the present results support the hypothesis that ruminative processing particularly of a verbal-worry variety is associated with an increase in intrusive images following exposure to stressful stimuli. These results are consistent with the view that active worry may contribute to the development of emotional difficulties marked by subjectively uncontrollable intrusive thoughts (Wells, 1994b; Wells and Matthews, 1994). Whilst this may be relevant in the sequelae of post-traumatic stress, it may also be important in the etiology and maintenance of other forms of intrusive thought. For example, Wells and Morrison (1994) suggest that ruminative appraisal in the form of worry about intrusions may be involved in the transformation of normal obsessions into pathological varieties.

One of the implications arising from the results of this study is that it may be possible to identify the processing characteristics of subjects which increase the likelihood of intrusions following stressful experiences. Worry-prone subjects and individuals who show a tendency to engage in ruminative post-event processing may be more vulnerable to emotional after-effects of stress. More specifically, some individuals appear to use worry as a means of distracting from other types of thought which are more threatening (Wells and Hackmann, 1993; Borkovec and lnz, 1990; Wells and Davies, 1994). These people may be particularly prone to intrusions and prolonged stress effects. In summary, the active re-cycling of distressing material in consciousness may be counterproductive for emotional and cognitive self regulation.

Acknowledgements--Adrian Wells is grateful to the Medical Research Council U.K. and the Wellcome Trust for their support.

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