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This study compared the effects of suppression, focused-distraction, and concentration on controlling unwanted distressing thoughts, and examined how anxiety levels were associated with the use of each thought-control technique. In the study, college students were told to suppress thoughts about a distressing story, to suppress the same thoughts by focusing on an alternative distraction task, to simply concentrate on that alternative task, or to think about anything without restrictions for 6 minutes. This initial period was followed by a “free-thinking” period to assess the delayed effect of thought-control techniques. The results indicated that focused-distraction and concentration led to fewer intrusions of target thoughts than suppression, and concentration in turn resulted in fewer target intrusions than focused-distraction during the initial period. Participants in the focused-distraction and concentration condition also tended to report lower anxiety during the initial period than those who were told to suppress thoughts.

It is very common for people to experience unwanted intrusive thoughts (Rachman & de Silva, 1978; Salkovskis & Harrison, 1984). Salkovskis and Harrison (1984) found that 88% of the non-clinical subjects in their study reported experiencing unwanted thought intrusions. When an unwanted thought occurs, people may try to deal with it by avoiding it (Folkman & Lazarus, 1991; Lazarus, 1966). This tendency to suppress one's unwanted thoughts in order to achieve a sense of well-being has been suggested in Freud's (1975) work. Yet, the effect of thought suppression has not been systematically examined until recently. In Wegner, Schneider, Carter, and White's (1987) research, half of the subjects were first instructed to “try not to think of a white bear” for 5 min and then to think of it in the next 5 min (the initial suppression condition), whereas the other half of the subjects received the same instructions in the reverse order (the initial expression condition). The results showed that subjects who had initially suppressed thoughts of a white bear experienced more such thoughts during the expressive period than those who had not initially suppressed target thoughts. Therefore, this may suggest that the suppression attempt may ironically cause people to be preoccupied with the unwanted thoughts even more after the suppression attempt ceased. Wegner and his colleague thus called this paradoxical phenomenon of thought suppression the “rebound effect.” To date, more research has accumulated in the area of thought suppression (e.g., Brewin & Beaton, 2002; Höping & de Jong-Meyer, 2003; Markowitz & Borton, 2002; Oliver & Huon, 2001; Parkinson & Rachman, 1981; Rassin & Diepstraten, 2003; Rassin, Merckelbach, & Muris, 2000; Rassin, van Brakel, & Diederen, 2003; Renaud & McConnell, 2002; Rutledge, 1998; Rutledge, Hancock, & Rutledge, 1996; Tolin, Abramowitz, Hamlin, Foa, & Synodi, 2002), but the findings remain mixed (Abramowitz, Tolin, & Street, 2001; Wenzlaff & Wegner, 2000) in that some studies have found the postsuppressional rebound effect (e.g., Kelly & Kahn, 1994; Muris, Merckelbach, van den Hout, & de Jong, 1992; Wenzlaff & Bates, 2000), but some studies found the immediate enhancement effect of suppression (e.g., Lavy & van den Hout, 1990; Muris et al., 1992; Turner & Engle, 1989), while other studies did not find any ironic effects (i.e., the rebound or immediate enhancement effect) due to suppression (e.g., Davies & Clark, 1998; Purdon & Clark, 2001; Roemer & Borkovec, 1994; Rutledge, Hollenberg, & Hancock, 1993). Therefore, it seems that the paradoxical effect of thought suppression is not a phenomenon that occurs consistently. One of the factors that are believed to influence the effects of thought suppression is the method that people use to control their thoughts (Cioffi & Holloway, 1993; Salkovskis & Campbell, 1994; Salkovskis & Reynolds, 1994; Wegner et al., 1987). The negative-cuing hypothesis (Wegner et al., 1987; Wegner, Schneider, Knutson, & McMahon, 1991) suggests that the rebound effect is more likely to occur when people suppress thoughts by focusing on items found in the immediate environment for self-distraction since those distracters may later become associated with the negative cue—“not white bear”, thus reminding people of the target thoughts after the suppression attempt is lifted. On the other hand, research showed that the rebound effect may not occur when people suppress target thoughts by focusing on only one distracter. For example, Wegner et al. (1987) found that subjects who were told to suppress the thought of a white bear by thinking of a “red Volkswagen” (the focused-distraction” condition) did not experience the postsuppressional rebound effect, whereas those in the typical suppression condition experienced a rebound during the subsequent expression period. These results thus suggest that suppressing thoughts by focusing on a specific, non-environment-associated distracter may serve as a strategy to attenuate the postsuppressional rebound effect. Salkovskis and Campbell's (1994) study provided further evidence of the positive effects of focused-distraction. In their study, two types of distraction conditions were compared: one was General Distraction (no specific distracters provided), while the other was Specific Distraction (a specific distraction task was provided to focus on). They found that simply instructing subjects to suppress personal negative thoughts by self-distraction without informing them of what to focus on did not work any better than the traditional suppression instruction in which subjects were simply told to suppress their thoughts. In contrast, when told to suppress target thoughts by focusing on a given distraction task, subjects not only experienced no postsuppressional rebound effect during the subsequent free-thinking period but also experienced significantly fewer target thoughts than the suppression-alone and the general-distraction groups during both experimental periods. Similar results were found with the suppression of thoughts about smoking (Salkovskis & Reynolds, 1994) and thoughts of physical pain (Cioffi & Holloway, 1993). In Salkovskis and Reynolds’ (1994) study, subjects who were told to suppress thoughts by focusing on a specific distraction task (i.e., a breathing exercise) did not experience a postsuppressional increase in target thoughts and also experienced fewer smoking thoughts than the suppression group during the suppression and subsequent free-thinking periods. In addition, subjects in the focused-distraction condition reported less discomfort relative to occurrences of smoking-related thoughts than did those in the other conditions. Similarly, Cioffi and Holloway (1993) found that participants who were told to distract themselves by visualizing the details of their room at home recovered from their discomfort (induced from immersing hands in the ice-cold water) more quickly than those who were told to not think about their hand sensations. Based on the findings of the above research, it seems that the focused-distraction strategy might be more effective than the suppression strategy in reducing unwanted thoughts or at least attenuate the immediate thought enhancement or the rebound effect of thought suppression. Although the underlying reason for this has not been clarified, it can be speculated that, to the extent that people rely on multiple distracters (according to the negative-cuing hypothesis) or multiple ways to suppress unwanted thoughts, people will alternate focus from one distracter to another or frequently think about how to suppress thoughts, thus rendering more possibility for target thoughts to intrude during those breaks. If this reasoning is true, it can be predicted that the concentration strategy—concentrating on pursuing an alternative goal with no intentions of suppression—would be even more effective than the focused-distraction strategy on controlling unwanted thoughts. However, very few studies have directly investigated the effects of concentration within the context of thought suppression. One study by Wenzlaff and Bates (2000), which compared the effects of concentration and suppression strategies in the completion of a scrambled sentence task, may provide implications for the effect of the concentration strategy in controlling unwanted thoughts. In their study, subjects in the concentration condition were told to unscramble sentences to form positive statements, whereas subjects in the suppression condition were told to not form negative statements. The control group was instructed to unscramble whatever came to mind first. The results of their first study showed that the concentration group unscrambled a lower percentage of negative statements than did either the control group or the suppression group, while the suppression group and the control group did not differ significantly. Their second study showed that the suppression group unscrambled more negative statements during the subsequent free-unscrambling period than did the control group and the concentration group. These results seem to suggest that the concentration strategy may prevent the delayed increase of unwanted cognitions and also might be more effective than the suppression strategy in reducing unwanted cognitions. Wenzlaff and Bates’ (2000) study may serve as an initial look of the effect of the concentration strategy on mental control. However, interpretations with respect to real-life thought-control behaviors should be made cautiously since the use of a scrambled sentence task to measure how well the subjects achieved the goal of avoiding certain constructs (negative statements) is far from everyday thought-suppression contexts or in typical thought-suppression research. Therefore, more evidence, particularly evidence derived from the more typical thought-suppression research paradigm is needed before firm conclusions on this topic can be drawn. In sum, the existent research and theories (Liberman & Förster, 2000; Martin, Tesser, & McIntosh, 1993; Muris et al., 1992; Wegner, 1994; Wegner & Zanakos, 1994) seem to suggest that suppression is a relatively ineffective strategy in reducing unwanted thoughts, compared with focused-distraction or concentration. Besides that, some research showed that suppression of an unwanted thought may also be associated with some negative affect. Roemer and Borkovec (1994) found that suppressing thoughts led to an increase in anxiety at the end of the experiment regardless of distressing or neutral thoughts that had been suppressed. In addition, Trinder and Salkovskis’ (1994) study indicated that higher suppression efforts were associated with higher levels of discomfort over thought occurrences, while the levels of discomfort correlated positively with a clinical measure of anxiety for participants who were instructed to suppress thoughts. The notion that suppression may increase anxiety could probably be inferred from the theory of psychological reactance (Brehm, 1966; Brehm & Brehm, 1981) in that restrictions and regulations could be perceived as threats to one's freedom, and thus induce an unpleasant state of arousal. It is also possible that anxiety could result from intrusions of unwanted thoughts during suppression (Trinder & Salkovskis, 1994) either because the thought contents are distressing or because the thought intrusions represent a failure in achieving the goal of mental control, or due to both reasons. As described above, the method that people use to control their thoughts may affect the research findings. Besides that, methodological variations may also lead to differing results among studies. Clark, Ball, and Pape (1991) argued that the postsuppressional rebound effect found in Wegner et al. (1987) was probably due to the fact that the initial suppression group (who first suppressed thoughts and then expressed thoughts) had more practice with the thought-recording technique than the initial expression group. Moreover, Clark et al. (1991) speculated that the use of expression as the instruction for the control condition was more likely to produce a ceiling effect and thus the immediate enhancement effect might be harder to detect. Therefore, Clark and his colleagues’ (Clark et al., 1991; Clark, Winton, & Thynn, 1993) studies asked the suppression group to first suppress the target thought, followed by a liberal-expression period, while asking the control group to think about whatever they wanted for both experimental periods. The postsuppressional rebound effect was then measured by comparing the frequency of target thoughts during the second (liberal expression) period for the suppression group and the control group. As seen in the literature, most studies (e.g., Clark, Ball, & Pape (1991) and Clark, Winton, & Thynn (1993); Davies & Clark, 1998; Harvey & Bryant, 1998; Muris et al., 1992; Purdon & Clark, 2001; Roemer & Borkovec, 1994; Wegner & Gold, 1995) that used Clark and his colleagues’ design found that the control group experienced a decrease in target thoughts between Period 1 and Period 2. This is probably due to a habituation effect, a loss of interest in thinking about the target thoughts (Wegner & Gold, 1995), or the exhaustion of a limited number of target thoughts (Purdon & Clark, 1997) for the control group. Given that the control group experienced a decrease in target thoughts from Period 1 to Period 2, the postsuppressional rebound effect, as defined by Clark et al. (1991), would be more likely to be found. Although Clark et al.'s (1991) design solves the possible practice problem in Wegner et al.'s (1987) original design, it nevertheless creates ambiguity in interpretation of the rebound effect, as Roemer and Borkovec (1994) mentioned. To prevent the ecological problem of using expression as the control condition, the present study used “free thinking” as the instruction for the control condition to better imitate real-life situations (Lavy & van den Hout, 1990; McNally & Ricciardi, 1996; Merckelbach, Muris, van den Hout, & de Jong, 1991). Moreover, to avoid the interpretation problem associated with a decrease in target thoughts between periods for the control group, the postsuppressional rebound effect was assessed by comparing the subsequent period (the free-thinking period) for the experimental groups with the initial period (the first free-thinking period) for the control group. Overall, the present study sought to investigate whether the suppression, focused-distraction, and concentration strategies would result in differential effects on controlling unwanted distressing thoughts. In addition, the relationship between anxiety levels and each thought-control condition was also investigated. This study hypothesized that, for the suppression period, the suppression strategy would lead to more intrusions of the target thoughts than the focused-distraction and concentration strategies. And also, the focused-distraction strategy would lead to more intrusions of the target thoughts than the concentration strategy. It was also predicted that, for the subsequent free-thinking period, the suppression strategy would lead to more intrusions of the target thoughts than the focused-distraction and concentration strategies. Also, the focused-distraction strategy was expected to lead to more intrusions of the target thoughts than the concentration strategy. Moreover, this study hypothesized that a postsuppressional rebound effect would be observed in the suppression condition while no postsuppressional rebound effects would be observed in the focused-distraction and concentration conditions. These hypotheses were based on Wegner and his colleagues’ theory of ironic processes (Wegner, 1994; Wegner & Erber, 1992; Wegner & Zanakos, 1994), Liberman and Förster's (2000) motivational theory, and Muris et al.'s (1992) increased saliency theory. Furthermore, it was expected that target-thought intrusions in the suppression condition would be no greater than those in the non-suppression control condition during Period 1, whereas the focused-distraction and concentration conditions would lead to fewer intrusions of the target thoughts than would the non-suppression control condition during the same period. These hypotheses were based on the findings of prior research (Harvey & Bryant (1998) and Harvey & Bryant (1999); McNally & Ricciardi, 1996; Muris et al., 1992; Purdon & Clark, 2001; Roemer & Borkovec, 1994; Salkovskis & Reynolds, 1994; Wegner et al., 1987; Wenzlaff & Bates, 2000). In addition, it was predicted that the suppression group was expected to experience higher levels of anxiety than the focused-distraction and concentration groups during Period 1. These hypotheses were based on Liberman and Förster's (2000) theory, which states that suppressing a thought may induce a need to express this very thought. Therefore, it can be speculated that during suppression subjects would experience a conflict of need (expression) versus goal (suppression), which probably would induce increased uncomfortable arousal. In addition, these hypotheses were also consistent with Roemer and Borkovec's (1994) finding that suppressing thoughts produced increased anxiety at the end of the experiment.

Preliminary analyses A comparison of two forms of the word-completion test: As mentioned previously, there are two forms of the word-completion test and these two forms were counterbalanced for order of presentation. A t-test was conducted to test the differences between the scores on Form 1 and Form 2. Results indicated that the mean scores on Form 1 (Time 1: M=3.42, SD=1.99; Time 2: M=3.00, SD=1.54; n=50) and Form 2 (Time 1: M=3.20, SD=1.51; Time 2: M=3.30, SD=1.36; n=50) did not differ significantly at either Time 1, t(98)=.62, p=.535, or Time 2, t(98)=−1.03, p=.304. This suggests that the word-stems used in one form did not differ significantly from those in the other form in terms of the number of target words induced. A comparison of four conditions in Period 1 Frequency of target thought intrusions: Planned comparisons were performed to compare the number of target thoughts reported for Period 1 among the suppression, focused-distraction, concentration, and control conditions (note that the data analyzed here were obtained from subjects’ retrospective estimations). Consistent with the hypotheses, the results showed that participants in the suppression condition reported more target thoughts than those in the focused-distraction condition, t(40.10)=2.67, p=.011, and in the concentration condition, t(29.46)=4.50, p<.001. Subjects in the focused-distraction condition in turn reported more target thoughts than those in the concentration condition, t(35.56)=2.25, p=.031 (see Table 1 for means and deviations).