Thought suppression

Thought suppression is the process of deliberately trying to stop thinking about certain thoughts (Wegner, 1989). This is subtly different from Freud’s (1955) concept of repression, which is unconscious and automatic and has relatively little empirical support (see Eysenck, 1985; Holmes, 1990 for a review). Conversely, over thirty-five experiments to date have successfully found evidence for thought suppression and its effectiveness. This article will draw upon these studies showing that thought suppression produces paradoxical effects for personally irrelevant and relevant thoughts at both a mental and a behavioural level and that whilst Wegner’s (1994) Ironic Process Theory is adequate accounting for this a greater consideration of individual differences within this account might better explain evidence. With such evidence one can only guess the long term effects on the brain. Thought suppression is strongly associated with obsessive-compulsive disorder, in which a sufferer will repeatedly (usually unsuccessfully) attempt to prevent or "neutralize" intrusive distressing thoughts centered around one or more obsession, with compulsive mental or physical acts.

Empirical work
In order for thought suppression and its effectiveness to be studied researchers have had to find ways of tapping the processes going on in the mind so that they may be described. One such paradigm by Wegner, Schneider, Carter & White (1987) was to ask people not to think of a target (e.g. “white bear”) for five-minutes but if they did to ring a bell. After this, participants were told to think about the target for five-minutes more. Compared to those who had not used suppression there was evidence for unwanted thoughts being immediately enhanced during suppression and, furthermore, a higher frequency of target thoughts during the second stage, dubbed the rebound effect (Wegner, 1989). This effect has been replicated with different targets (Lavy & Van den Hout, 1990) and even implausible targets like “green rabbit” (Clark, Ball, & Pape, 1991). However, whilst this is good evidence for thought suppression causing increased immediate and/or delayed target thoughts several critical points can be raised. Firstly, typical thought suppression may not involve simple targets like coloured animals but socially more complex and personal thoughts. Secondly, the time frame used in these studies is only representative of thought suppression in short spaces of time, which may not accurately mirror typical human behaviour where longer term suppression (like trying not to think about recent ex-partner) may be manifest. Thirdly, the paradoxical effects could be elicited by the act of ringing the bell alone. Therefore, although there is good laboratory evidence for the poor effectiveness of thought suppression confidently projecting such findings onto naturalistic behaviours is conceivably problematic.

Improved methodology
To resolve this some studies have changed the target thought from a personally irrelevant to relevant one. Roemer and Borkovec (1994) found that participants who suppressed anxious or depressing personal thoughts showed a significant rebound effect compared to those who expressed the thoughts from the outset. Furthermore, Wenzlaff, Wegner, & Roper (1988) demonstrated that anxious or depressed subjects were less able to suppress negative unwanted thoughts. Despite Rassin, Merkelbach and Muris (2000) reporting that this finding is moderately robust in the literature some studies were unable to replicate results (e.g. Smári, Sigurjónsdóttir, & Sæmundsdóttir, 1994; Kelly & Kahn, 1994; Wegner, Quillian, & Houston, 1996). However, this may be explained by a consideration of individual differences. Recent research by Geraerts, Merckelbach, Jelicic, & Smeets (2006) found that for individuals with low anxiety and high desirability traits (repressors) suppressed anxious autobiographical events intruded fewer times than in other (low, high and high defensive anxious) groups initially but showed more intrusions 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 promoted Clarke, Ball and Pape (1991) 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 overcomes 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, where participants may lower their reported frequencies so as to avoid the risk of being pejoratively labelled.

Thought suppression in the behavioural domain
A reaction to this has been to explore the effects of thought suppression using more reliable measures, like behaviour. Macrae, Bodenhausen, Milne, and Jetten (1994) found that when asked not to think about the stereotype of a certain group (e.g. a ‘skinhead’) individuals’ written descriptions of a group member’s typical day contained less stereotypical thoughts than that of controls. However, when told they were going to meet such an individual those in the suppression condition sat significantly further away from the seat the ‘skinhead’ had evidently occupied moments earlier (by virtue of his clothes being present). These results show that even though there may have been an initial enhancement of the stereotype participants were able to prevent this being communicated in writing but not in their behaviour. Further experiments have documented similar findings (e.g. Cioffi and Holloway, 1993; Wegner, Shortt, Blake, and Page, 1990). However, another criticism that can be made of all these experiments is that they may not be accounting for the plausible strategy of naturalistic thought suppression to find distracters. To this end, participants were given cognitively demanding concurrent tasks and the results showed a paradoxical higher frequency of target thoughts than controls (Wegner & Erber, 1992; Wegner, Erber & Zanakos, 1993). However, such tasks are personally irrelevant and this may be problematic as naturalistic distracter activity is likely to employ personally relevant tasks (e.g. phoning a friend when trying not to think of an ex-partner). Nevertheless, Wegner, Schneider, Carter & White (1987) found that a single distracter (e.g., a red Volkswagen) was sufficient to eliminate the paradoxical effect. Therefore it would seem a high cognitive load acts to reduce the effectiveness of thought suppression but that using a focused target can improve the effectiveness. This is important because it may mean that in experimental conditions participants are deliberately finding multiple distracters during suppression, which may not be how successful naturalistic thought suppression operates. That is successful suppression may involve less distraction. Evidence from Bowers and Woody (1996) is supportive with the finding that hypnotized individuals produce no paradoxical effects. This rests on the assumption that deliberate distracter activity is bypassed in such an activity.

Cognitive dynamics
The evidence so far presents thought suppression as typically ineffective activity causing an ironic increase in the to-be-suppressed thought which is exacerbated when the cognitive load is increased. The picture is complicated by some studies being unable to find this effect for emotional thoughts, in hypnotized individuals, and when one distracter is used. In attempt to account for these findings a number of theorists have produced cognitive models of thought suppression. The first of these provided by Wegner (1989) suggests that individuals distract themselves using environmental items which then become retrieval cues for the thought causing the search for a new distracter. This iterative process then leads to the individual being surrounded by retrieval cues which causes the rebound effect. Certainly the evidence for multiple distracters is supportive but it cannot explain the initial thought enhancement or the single distracter results. As a result Wegner (1994) suggested the ‘Ironic Process Theory’ where two opposing mechanisms are at work. The first unconsciously monitors for occurrences of the unwanted thought calling upon the second should it find something. The second process is conscious and scans for distracters. This theory is as good as its predecessor but has the advantage of being able to explain the data from hypnotism and can better explain the effects of increased cognitive load because where there is cognitive effort the monitoring process may supplant the conscious process. Moreover, assuming no retrieval cue is forged it is able to explain how one distracter can make thought suppression effective. This is because there is an ideal balance between the two processes with the cognitive demand not being too great as to let the monitoring process supersede it. However, while it can account for the findings of that suppression of emotional thoughts leads to increased frequency of intrusions (because emotions interfere with the conscious process) it cannot do so in a way that is completely satisfactory as some studies do not find evidence that this is the case. As recent research suggests (e.g. Geraerts et al., in press) there may be an important role of individual differences that may be able to account for this however.

Summary
As time has progressed experiments have become more elaborate and better able to extend their findings to naturalistic thought suppression. The results of these studies are not encouraging in as much as they have demonstrated that trying to suppress impersonal and, on the face of it, personal thoughts is ineffective as the frequency of that thought increases during suppression and after it. Importantly, whilst the evidence shows that we can control these thoughts from being translated into behaviour when self-monitoring is high such control is not observable in normal, automatic behaviours (i.e. skinhead scenario). In addition, 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 not properly reflect natural processes. However, when only one distracter is used thought suppression has been shown to be successful. In explaining these results Wegner’s (1994) ‘Ironic Process Theory’ (where two processes monitor and search for distractions) is the most appropriate model; however, given the mixed evidence for emotional thoughts and commensurate with the latest research it is suggested that a model needs to account for individual differences to be considered robust. Thus, it can be concluded that thought suppression is a real phenomenon with observable effects and that typical results show it is largely an ineffective activity in the laboratory at least.