Mechanisms and Effectiveness of Imagery Strategies in Reducing Disgust in Contamination-Related Obsessive–Compulsive Disorder: Comparing Imagery Rescripting, Imagery Self-compassion and Mood-Focused Imagery

Forty-eight subjects volunteered to participate in this study. All the participants were native German speakers. The healthy control group participants were screened by telephone before being invited to the first appointment, to ensure that they matched the inclusion criteria. The participants had to be aged between 18 and 65 years old and have no history of or be currently diagnosed with, neurological disorders, traumatic brain injury, tic disorder, psychotic or bipolar disorder, substance abuse, or dependence. All the healthy control participants were paid 9.50 €/h for participating in the experiment.

Fourteen pictures were selected from the validated Disgust-RelaTed-Images database (DIRTI, Haberkamp et al., 2017).¹ The pictures were associated with fourteen questions about disgust-related situations, which participants answered before the actual experiment began. This was supposed to ensure that only pictures that were individually regarded as really disgusting, were presented. The questions were related to typical contamination-related disgust categories, like spoilage (e.g. “You will find mold on the chocolate pudding.”) and hygiene (e.g. “A toilet is full of urine.”). The complete set of images and questions are listed in Appendix 1. There were 7 questions and pictures for each of the two disgust categories. All the pictures were 16 cm wide and 12 cm high and were presented on a white, 30.5 cm wide and 13.5 cm high, screen. The participants were seated in front of the screen, about 50 cm from it, and responded by using a keyboard. The MATLAB © based PsychToolbox (Brainard, 1997; Kleiner et al., 2007; The MathWorks Inc., 2019) was used to run the experiment on a ThinkPad Laptop with a 14'' TFT monitor.

As in the study carried out by Fink et al. (2018), the experiment started with 14 written questions, which were used to select the six pictures to be presented in the experiment (see Section “Procedure”). On the first day, the participants were first informed of the details of the study and the test subjects’ written consent to participation was obtained (informed consent was given). The participants then had to fill out the questionnaires listed above. So that the disgusting images caused an aversive experience for the test person, they were individually selected by means of an a priori survey of different disgust categories (see Section “Stimuli and Material”). Thereafter, the participants were instructed to look at the screen, on which the individually selected disgusting picture was presented for 10 s. The participants were then asked to indicate how much the picture disgusted them on a 7-point Likert scale (0 = not at all, 6 = very disgusted). One of the three experimental conditions was then performed (imagery self-compassion, imagery rescripting, passive positive imagery condition, see section “Experimental Condition: Imagery Rescripting”, “Experimental Condition: Imagery Self-Compassion”, “Experimental Condition: Passive Positive Imagery Condition”), followed, on both days, by the two other intervention conditions, for which audible instructions were given over headphones, in a randomized order. The target picture was shown again for 10 s after each experimental condition, and the participants were asked to indicate, again on a 7-point Likert scale, how disgusted by the picture they now were. Finally, all the participants were asked to write down what they had actually done during the intervention on a white sheet of paper (e.g. I thought of something else), to determine whether the change in their disgust experience was due to the intended manipulation or another internal process. A new disgust picture was selected and shown for each session. Each participant performed all the three experimental conditions two times, over 2 days. The experimental conditions were performed in a randomized order, and none were repeated on the same day. The same picture was presented before (t1) and after (t2) the experimental condition in each experimental block. Therefore, each participant saw a total of six pictures. The two-session design was used to control for reliability and sequence effects through within-person repetition. The period of at least 1 week between sessions was chosen to reduce memory effects of the interventions. The number of days roughly aligns with the study by Fink et al. (2018). The course of the experiment is shown as an example in Fig. 1.

To test for baseline effects, a 3 × 2 ANOVA with the dependent variable initial disgust experience (t1) revealed no baseline differences for imagery strategy, but a significant baseline difference for group, F(1, 126) = 21.831, P < 0.001, η² = 0.15. A further investigation on the initial disgust experience (t1), revealed that being in the healthy control group was associated with a smaller disgust experience at t1, M = 4.319, SD = 0.81, compared to being in the clinical group, M = 5.219, SD = 0.611, t(42.77) = − 4.344, P < 0.001, d = 1.254. These results show that individuals did not rate images differently at baseline between the experimental conditions (within-person), though there were between-subject differences between the two groups for the initial disgust experience.

The habitual use of imagery (b = − 0.018, P = 0.004) and disgust propensity (b = 0.008, P = 0.01) were significant predictors of the difference in disgust experience between t1 and t2 in a linear regression model. A higher habitual use of imagery trait was associated with more disgust reduction between t1 and t2, and also that higher disgust propensity was associated with less disgust reduction between t1 and t2. All other traits were not significant predictors. The overall model fit was R² = 0.087.

When initial disgust experience (t1) was predicted in a linear regression model, disgust propensity (b = 0.015, P < 0.001) and negative affectivity (b = 0.037, P = 0.028) were significant predictors. Therefore, higher disgust propensity, as well as higher negative affectivity, were associated with a stronger initial disgust experience (t1). All other traits were not significant predictors. The overall model fit was R² = 0.108.

In order to present the results referring to the dichotomous variable (e.g. in the CFT condition, "Were you able to build up a compassionate self?" yes/no), qualitative response, group and imagery strategy were tested in the context of a 3 × 2 × 2 ANOVA with mixed measures on the dependent variable disgust reduction between t1 and t2. Here, a significant main effect was found for qualitative response with respect to disgust reduction between t1 and t2, F(1, 275) = 6.759, P = 0.009, η² = 0.04. According to this, the participants who themselves stated that they had successfully completed the task, M = − 0.834, SD = 1.186, reduced their disgust experience between t1 and t2 more strongly across all conditions and groups, than those who stated that they had not successfully completed the task, M = − 0.375, SD = 0.787. However, when considering the frequencies with which the subjects rated the interventions as successful or unsuccessful, a 3 × 2 ANOVA with mixed measures shows a significant main effect for imagery strategy, F(2,92) = 3.014, P = 0.009, with more successful ratings in the passive positive imagery condition (n = 78) and the ImR condition (n = 76), than in the CFT condition (n = 63). In addition there is a significant main effect for group, F(1,56) = 5.593, P = 0.022, as there were more successful responses in the healthy group (n = 122) compared to the clinical group (n = 95). Overall, an average of 42.5 statements about helpful aspects of the CFT strategy and 38.5 statements about difficulties with the same strategy, were encoded. For ImR, it was possible to encode an overall average of 62.5 statements on helpful aspects and 14.5 statements on those that caused difficulties. Participants did not give enough information about why the passive positive imagery condition was helpful or difficult to implement and these where therefore not analyzed. Participants reported aspects in all of our a priori theoretically derived categories, albeit with varying frequency. How often each category was mentioned is shown in Table 2.

We are aware of some limitations to our study. The first limitation is the gender ratio of 83% women. A more equal gender ratio might control for disgust-specific gender effects, taking into account the idea that women tend to be more sensitive to disgust (Schienle et al., 2005). Nonetheless, exactly the same results were found by recalculating all the results and excluding the four male subjects in each group; therefore, our results have to be seen as applying primarily to women. A second limitation is that the content analysis on subjectively perceived strategies could not be applied to the passive positive imagery condition. This was because the participants did not give enough information about why the strategy was helpful or difficult to implement. In a future study, the questions should be asked in such a way that participants are more motivated to answer these questions. Third, a fundamental problem is that the 7-min interventions and 10-s picture presentations reduced the ecological validity and promoted distraction effects. In the long run, it will be important to perform longer, and more elaborate, interventions regarding idiosyncratic disgust, preferably in a face-to-face setting. Due to the current study design enduring effects of imagery could not be investigated. To test this in future studies, short interventions would have to be presented more frequently or the effect would have to be recorded in the short term (e.g., on the next day) (see the studies on imagery rescripting by Kunze et al., 2017; Siegesleitner et al., 2019). A fourth limitation could be that habituation effects could not be tested directly, because a non-imagery condition was not included. However, previous studies (Fink & Exner, 2019; Fink et al., 2018) have shown the effectiveness of imagery rescripting compared to a habituation control condition. A methodological consideration is that by stringing the three blocks together, the experience of disgust was magnified, which is evident in the main effect block. Emotional sensitization by repetition of disgust experience in well known in other studies (Fink-Lamotte et al., 2020). While these processes should not have influenced the main hypotheses here due to randomization and the focus on within-block change, it is nonetheless important to keep a closer eye on this in future studies.

The aim of this study was to investigate how effectively and by what mechanisms, three different imagery strategies reduced disgust in the context of C-OCD. Particularly in comparison with the results of Fink et al. (2018)—including a habituation control condition and an imagery rescripting condition—the results show that all three strategies were equally capable of reducing disgust on all levels of disgust experiencing. This provides further evidence of the benefits of imagery strategies in altering pathological disgust. The results also show that the success of imagery strategies is related to the subject’s ability to use imagination. Special attention should be paid to this when implementing imagery strategies in a therapeutic setting and, in case of doubt, preliminary exercises should be performed (also in future studies). In the elaborate content analysis it was shown, that participants who reported the theoretically assumed mechanisms of the strategies and considered the intervention itself to have been a success, were better at reducing disgust. Even though it seems that “many roads lead to Rome” in the context of changing disgust through imagery, the difference between more active and more passive imagery strategies should be further investigated in future studies.