Thought Suppression
Richard M. Wenzlaff and Daniel M. Wegner
Annu. Rev. Psychol. 2000. 51:59-91.
 

Abstract

Although thought suppression is a popular form of mental control, research has indicated that it can be counterproductive, helping assure the very state of mind one had hoped to avoid. This chapter reviews the research on suppression, which spans a wide range of domains, including emotions, memory, interpersonal processes, psychophysiological reactions, and psychopathology. The chapter considers the relevant methodological and theoretical issues and suggests directions for future research.

Introduction

There is a certain predictability to unwanted thoughts, a grim precision in the way our mental clockwork returns such thoughts to mind each time we try to suppress them. As a result, it is tempting to attribute special significance or power to suppressed thoughts, to see them as expressions of sinister workings of mind—and in fact, it was exactly this approach that led Freud (e.g. 1953) to focus his attention on the nature of thoughts that are expelled from consciousness. As it turns out, however, it may not be especially useful to ascribe significance to unwanted thoughts themselves.

Contemporary research suggests that it is the process of thought suppression, not the product, that should be examined for its significance and power. This realization has emerged from studies in which people are instructed to spend time trying not to think about some particular thought, however neutral or mundane, with the consequences of their activity being measured. Early research hinted that such instructions might make such a thought tend to return (e.g. Antrobus et al 1964, Langfeld 1910). This finding was most pronounced in the "white bear" studies of Wegner et al (1987), and the introduction of this standardized laboratory paradigm has yielded substantial evidence that the paradoxical nature of the process of thought suppression is responsible for the returning of unwanted thoughts to mind.

Evidence on thought suppression is accumulating broadly at a rapid pace. Although there are reviews of aspects of this literature (Beevers et al 1999; Bodenhausen & Macrae 1996; Monteith et al 1998a; Purdon & Clark 1999; Wegner 1989, 1992; Wegner et al 1994a; Wegner & Wenzlaff 1996), the topic deserves an integrated and current review. We endeavor to provide this by focusing on research on the process of thought suppression that has accrued since the white bear studies. We begin by describing the phenomenon—when suppression is apt to backfire—and the methodological considerations relevant to the detection of this paradoxical effect. Next, we consider the main theoretical accounts for this outcome and examine the key variables that may mediate the effects of thought suppression. We then review the impact of suppression on intrapersonal states (e.g. emotional, cognitive) and interpersonal processes (e.g. attraction, prejudice), and finally we consider the relationship of thought suppression to psychopathology.
 

The Phenomena

Researchers have identified three classes of suppression-related effects: (a) enhanced occurrence of target thoughts following a period of suppression; (b) an immediate, suppression-induced surge in target thoughts; and (c) an intensification of intrusions during suppression, triggered by cognitive demands. In this section, we examine the evidence for these different suppression-related phenomena. First, however, we briefly discuss the importance of baseline considerations in assessing suppression-related effects.

Emptying the Head
What exactly does it mean not to think of something? If thought suppression were a perfect process, it would ideally leave a person with no vestige of the unwanted thought at all. The initial "white bear" experiments of Wegner et al (1987) compared thought suppression to this ideal and found it wanting. It was assumed in these studies that college students in Texas would almost never think of a white bear spontaneously, and therefore that any evidence of such a thought during suppression was an indication that suppression had failed. And indeed, many such indications were observed. Participants’ signals that the thought was occurring during a 5-minute suppression session—in the form of verbal reports or bell-rings to indicate the thought’s return—on average exceeded one per minute.

This frequency of thinking seems excessive if people can indeed suppress a thought completely, but perhaps this is too much to ask. After all, the instruction to suppress is a sort of reminder of the unwanted thought. Perhaps this instruction cues people to think of the target more than they would have normally. To control for such cuing, investigators have examined several comparisons, each implying a different baseline level of spontaneous thinking.

One baseline approach is the "free monitoring" method, in which participants are asked to report whatever comes to mind. This approach is appealing because it does not produce artificially high rates of target thoughts and avoids potential ceiling and exhaustion effects. It does not, however, control for cuing effects that can result when the suppression group is specifically instructed to inhibit a particular thought. Moreover, the monitoring condition can risk floor effects when natural baseline levels for a particular thought are very low. To avoid the problem of a zero baseline and to minimize differential cuing, this free-monitoring method typically requires that the experimental procedure expose participants to the thought target (e.g. in a film or a reading) prior to the thought reporting period.

Another possible comparison involves a "cued monitoring" or "mention" control. In this case, instructions mention the target thought, either alone or in the context of other thoughts, optionally with some instruction indicating that these are things the participant may or may not consider during the thought report period. In some cases, the participant is also asked to monitor the occurrence of the cued thought. This approach helps equate cuing for the suppression and control groups while minimizing ceiling and floor effects. Although this approach has several advantages, the "mention" instructions may promote excessive attention to the target and could distort responses by making participants suspicious about its role in the study. Indeed, the attempt to monitor a thought may be a component of the mental process of suppression, in which case monitoring serves as a seriously flawed baseline.

The third potential comparison is the "expression" method, in which control participants are instructed to think about the item that the suppression group is trying to inhibit. Not surprisingly, this control method produces high rates of target thoughts in the control condition, and so makes instructed suppression look very successful. Trying not to think of something produces far fewer thoughts than does trying to think of it on purpose—but this effect seems attributable to the effectiveness of expression, not the effectiveness of suppression. Expression is thus used more as an informative comparison condition than as a control. And expression conditions have come to be important in suppression research because of the discovery that prior suppression can enhance the degree of subsequent expression—the post-suppression rebound effect (Wegner et al 1987).