Thought suppression is a psychological defence mechanism. It is a type of motivated forgetting in which an individual consciously attempts to stop thinking about a particular thought. It is often associated with obsessive–compulsive disorder (OCD). OCD is when a person will repeatedly (usually unsuccessfully) attempt to prevent or "neutralize" intrusive distressing thoughts centered on one or more obsessions. It is also thought to be a cause of memory inhibition, as shown by research using the think/no think paradigm. Thought suppression is relevant to both mental and behavioral levels, possibly leading to ironic effects that are contrary to intention. Ironic process theory is one cognitive model that can explain the paradoxical effect.
When an individual tries to suppress thoughts under a high cognitive load, the frequency of those thoughts increases and becomes more accessible than before. Evidence shows that people can prevent their thoughts from being translated into behavior when self-monitoring is high; this does not apply to automatic behaviors though, and may result in latent, unconscious actions. This phenomenon is made paradoxically worse by increasing the amount of distractions a person has, although the experiments in this area can be criticized for using impersonal concurrent tasks, which may or may not properly reflect natural processes or individual differences.
Empirical work, 1980s
In order for thought suppression and its effectiveness to be studied, researchers have had to find methods of recording the processes going on in the mind. One experiment designed with this purpose was performed by Wegner, Schneider, Carter & White. They asked participants to avoid thinking of a specific target (e.g. a white bear) for five minutes, but if they did, they were told then to ring a bell. After this, participants were told that for the next five minutes they were to think about the target. There was evidence that unwanted thoughts occurred more frequently in those who used thought suppression compared to those who were not. Furthermore, there was also evidence that during the second stage, those who had used thought suppression had a higher frequency of target thoughts than did those who hadn't used thought suppression; later coined the rebound effect. This effect has been replicated and can even be done with implausible targets, such as the thought of a "green rabbit". From these implications, Wegner eventually developed the "ironic process theory".
Improved methodology, 1990s
To better elucidate the findings of thought suppression, several studies have changed the target thought. Roemer and Borkovec found that participants who suppressed anxious or depressing thoughts showed a significant rebound effect. Furthermore, Wenzlaff, Wegner, & Roper demonstrated that anxious or depressed subjects were less likely to suppress negative, unwanted thoughts. Despite Rassin, Merkelbach and Muris reporting that this finding is moderately robust in the literature, some studies were unable to replicate results. However, this may be explained by a consideration of individual differences.
Recent research found that for individuals with low anxiety and high desirability traits (repressors), suppressed anxious autobiographical events initially intruded fewer times than in other groups (low, high, and high defensive anxious groups), but intruded more often after one week. This difference in coping style may account for the disparities within the literature. That said, the problem remains that the cause of the paradoxical effect may be in the thought tapping measures used (e.g. bell ringing). Evidence from Brown (1990) that showed participants were very sensitive to frequency information prompted Clarke, Ball and Pape to obtain participants' aposterio estimates of the number of intrusive target thoughts and found the same pattern of paradoxical results. However, even though such a method appears to overcome the problem, it and all the other methodologies use self-report as the primary form of data-collection. This may be problematic because of response distortion or inaccuracy in self-reporting.