The first researcher to combine exposure with response prevention in the treatment of rituals was Meyer (1966). His `apotrepic therapy' was applied in an inpatient setting to patients with washing rituals and was used again later in follow up studies.

Treatment involved constant supervision by nurses to prevent patients from carrying out rituals. Many studies have shown exposure with response prevention to be a powerful, effective treatment for OCD (see Abel, 1993; Foa et al., 1985). By the mid-1970s, success rates ranged from 75-85% and relapse was not a problem (Foa & Goldstein, 1979; Marks et al., 1975).

In the mid-1980s, Foa et al. (1985) reviewed studies from several different countries and found that 51% of the patients showed at least 70% decrease in symptoms, and 39% showed between 30% and 69% decrease in symptoms. Moreover, 76% of them continued to be at least moderately improved at follow ups of months or years.

Ost (1989) reviewed seven studies using exposure and response prevention techniques in the treatment of OCD and found that 85% of the patients continued to retain the improvements made and that over 50% required no further therapy from one to three years after treatment. O'Sullivan and Marks (1991) reviewed nine studies that used exposure and response prevention techniques and found that, in all nine studies, the significant treatment gains following treatment were maintained at a mean of three (one to six) years, and no symptom substitution occurred.

At follow up, 79% of the patients were improved or much improved and 21% were unimproved. Recent reviews have found that once patients begin therapy, significant improvement is seen in 70-92% of the cases (Abel, 1993). However, Keijsers et al. (1994) have pointed out that the success rates most often reported in the literature do not take into account those who refuse behavior therapy or drop out of treatment. When these factors are considered, the success rate drops to 40-50%.

Most of the results reported above reflect the effects of in vivo exposure. However, imaginal exposure is also widely used. In imaginal exposure, patients imagine that a sequence of events takes place that leads to catastrophic outcomes. They are instructed to create a script describing this sequence and read it onto a loop tape. A loop tape is a cassette tape that continues to repeat the recorded script over and over again until the recorder is turned off.

Thus, a patient can concentrate on the obsessive thoughts and images for extended periods without interruption. The more horrifying the imagined outcome, the more successful the procedure. But how effective is it? At this point in time, the results of studies are inconsistent (Emmelkamp, 1993). However, some investigators have found that while imaginal exposure has not always produced satisfactory results, maintenance of treatment gains tend to be enhanced when it accompanies exposure in vivo (Foa et al., 1980b; Steketee et al., 1982).

In a recent pilot study, Lovell et al. (1994) found that there was a tendency for imaginal exposure to work with compulsive ruminators, provided that the tape contained only the anxiogenic (obsessive), and not the anxiolytic (neutralizing ritualistic), thoughts. This amounts to exposure and response prevention at the covert level. If the anxiolytic neutralizing thoughts are allowed on the tape, then the mental rituals are still reinforced because they reduce the anxiety associated with the obsessive thoughts.

The key to success is to practice long periods of exposure to anxiogenic thoughts while preventing anxiolytic thoughts. Imaginal exposure is also useful for those times when you would not wish to expose patients to their fears in vivo, such as letting a building burn down when the stove was not checked or dropping a baby that the patient is worried about dropping (Foa et al., 1985).

Although imaginal exposure is often useful, exposure in vivo is more effective (Greist, 1990b). Rabavilas et al. (1976) found that exposure in vivo was more effective than imaginal exposure in the treatment of OC symptoms, and that prolonged exposure is more effective than brief exposure when in vivo methods are used, but that it really doesn't matter when using imaginal exposure.