Evidence for proactive interference effects in repetitive checking tasks

Why does repeatedly checking one's actions, a common behaviour of those with obsessive-compulsive disorder (OCD), undermine memory confidence? The most accepted explanation is that repetitive checking decreases confidence by increasing familiarity with the task, leading to the encoding of fewer perceptual details. We argue that checking, per se, does not decrease memory confidence. Rather, the experimental procedure that has been used to assess checking across repeated trials induces proactive interference (PI), causing the drop in confidence. We conducted three experiments in which participants repeatedly checked three different food items in a virtual refrigerator, with memory accuracy and confidence tested after the first and last trials. All three experiments showed that recall of the items presented on each trial, and confidence in the accuracy of the recalled items, decreased across trials, implying a build-up of PI. Experiments 2 and 3 also demonstrated that providing a category cue on the last trial eliminated the decline, suggesting a release from PI. Moreover, Experiment 3 showed that checking within a specific trial increased accuracy and confidence. This result suggests that the decline across trials is due to PI and that checking, per se, improves accuracy and confidence. Implications for individuals with OCD are discussed.