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Rumination has been recognised as an important maintaining factor in depression. Adapting the mood-as-input theory to rumination, we hypothesised that high ruminators have a default “as many as can” stop rule for determining when to stop analysing the causes and consequences of any problem, such that negative mood signals insufficient problem solving, leading to recurrent analysis and self-focus (i.e. rumination). To explore this hypothesis, 60 participants were randomly instructed to continue generating reasons for a recent depressed mood under three conditions: an “as many as you can” stop-rule, an “as long as you feel like continuing” stop-rule, and a “no stop-rule” condition. Participants were split into high and low ruminators on a median split on Ruminative Response Scale scores. As predicted, the high ruminators in the “as many as you can” and “no stop rule” conditions produced significantly more reasons for their depressed mood (without significantly differing from each other), than either the high ruminators in the “feel like continuing” condition or the low ruminators in all conditions. These results suggest that high ruminators adopt a default “as many as can” stop rule and that teaching high ruminators to use a “feel like continuing” rule may reduce rumination.

Rumination has been increasingly recognised as an important component of depression. Nolen-Hoeksema, 1987 and Nolen-Hoeksema, 1991 defined rumination as thoughts and behaviours that focus the depressed individual's attention on his or her symptoms and the possible causes and consequences of those symptoms. Rumination therefore includes much of the repetitive and recurrent self-focused thinking found in depression, which includes analysing the reasons for failure and low mood. Such thinking is often characterised by questions, such as “Why did this happen to me? Why do I feel like this?”. The importance of rumination in depression has been further underlined by ruminative self-focus being a central tenet of important theoretical models of depression (Pyszczynski & Greenburg, 1987 and Teasdale & Barnard, 1993). Longitudinal studies have suggested that rumination is linked to the prognosis of depression and the maintenance of depressed mood. People who respond to depressed mood with rumination report more frequent, more severe and longer periods of depressed mood than those who distract or avoid focusing on their emotions (e.g. Just & Alloy, 1997, Nolen-Hoeksema et al., 1994, Nolen-Hoeksema et al., 1993 and Kuehner & Weber, 1999). Recently, Kuehner and Weber (1999) demonstrated that this effect generalizes to clinically depressed patients, with rumination predicting future levels of depression, independently of initial levels of depression. Furthermore, experimental studies have compared a rumination induction involving focus on depressed mood and its causes and consequences, with a distraction induction, in which people think about visual images unrelated to emotion. Relative to distraction, for participants in a dysphoric mood, rumination exacerbates depressed mood (Morrow & Nolen-Hoeksema, 1990 and Nolen-Hoeksema & Morrow, 1993), increases global negative attributions (Lyubomirsky & Nolen-Hoeksema, 1995) and the accessibility of negative memories (Lyubomirsky, Caldwell, & Nolen-Hoeksema, 1998) and reduces the effectiveness of problem solving (Lyubomirsky & Nolen-Hoeksema, 1995). Theories of rumination suggest that discrepancies in goal progress instigate rumination (Carver & Scheier, 1990, Martin & Tesser, 1989, Martin & Tesser, 1996 and Pyszczynski & Greenburg, 1987), with difficulties in disengaging from unfulfilled goals leading to chronic rumination and depression (Pyszczynski & Greenberg, 1987). These theories suggest that people who tend to experience more frequent or more salient discrepancies between their ideal goal outcomes and actual outcomes will experience more rumination. People often interpret their emotional states as evidence relevant to judging the status of their goals (Cervone et al., 1994, Frijda, 1988 and Schwarz & Clore, 1983). Thus, individual differences in interpreting affect as a sign of good or poor goal progress could also influence individual differences in the tendency to ruminate. However, whether positive or negative affect signals goal attainment or non-attainment depends upon the context in which the feelings occur (Martin & Stoner, 1995) and, in particular upon the explicit or implicit rules used by people in these situations (Martin, Ward, Achee, & Wyer, 1993). Martin et al. (1993) found that positive and negative moods had differential effects on the number of bird's names generated when participants were asked to continue under different stop rules. In a positive mood, asking participants to continue until they no longer felt like doing it (“feel like continuing” stop rule) produced more responses than asking participants to generate as many names as they could (“as many as can” stop rule). However, in the negative mood, the “as many as can” rule produced more responses than the “feel like continuing” rule. Martin et al. (1993) explained these findings in mood-as-input terms. In the “feel like continuing” condition, a negative mood signals that continuing with the task is no longer appropriate, thereby, initiating disengagement from the task. However, in the “as many as can” condition, the negative mood signals to participants that they have not made satisfactory progress on the task, leading to persistence on the task. Thus, the informational value of the mood, which depends on the orientation adopted to the task, rather than the mood itself, determines whether participants persist at the task. Individual differences in the adoption of these different stop rules could, therefore, influence whether positive or negative affect is interpreted as a sign of goal progress, and, thereby, influence the tendency to ruminate. Recently, Davey and Startup (2000) reported that explicitly manipulating the stop rules for catastrophic worry had differential effects for worriers and non-worriers. In an “as many as can” stop rule condition, worriers produced significantly more catastrophic worry steps than non-worriers but in a “feel like continuing” stop rule condition, worriers produced significantly fewer steps than non-worriers. Davey and Startup suggested that worriers have an implicit “as many as can” stop rule, consistent with the beliefs held by worriers that worry is useful for problem-solving and averting catastrophe (Borkovec et al., 1998, Davey et al., 1996 and Freeston et al., 1994). Thus, worriers are more likely to use a negative mood as a signal that they have not successfully completed a problem-solving task, and will therefore persist until they feel they have adequately considered all the possible aspects of the problem. Given that compared with low ruminators, high ruminators hold beliefs that rumination is helpful in increasing self-awareness and understanding depressed mood, and in solving problems and preventing future mistakes (Watkins & Baracaia, 2001), we hypothesised that high ruminators would have a default “as many as can” rule for problem-solving. Such a rule would maintain their rumination, since they would tend to interpret any negative mood as a sign that they had not completely explored a problem, leading to further analysis and self-focus. Furthermore, since ruminative self-focus exacerbates negative mood (Nolen-Hoeksema & Morrow, 1993), we hypothesised that high ruminators could get trapped in a reciprocal loop with negative mood and ruminative thinking maintaining each other. Therefore, this study was a preliminary investigation of whether mood-as-input stop rules can differentially influence rumination in high and low ruminators, and of whether high ruminators have a default “as many as can” stop rule. We used an adaptation of Davey and Levy's (1998) catastrophic interview as our rumination task, with participants asked to generate reasons for a current or past depressed mood. We assumed that high ruminators would be in a significantly more negative mood than low ruminators at the time of the study, because of the aforementioned studies demonstrating a link between rumination and depressed mood. Therefore, according to the mood-as-input theory, we predicted that high ruminators would generate significantly more reasons for their depression in an “as many as can” stop rule, compared with a “feel like continuing” stop rule. We further predicted that low ruminators would either have no significant difference in the number of reasons generated in an “as many as can” stop rule compared with a “feel like continuing” stop rule, or generate significantly more reasons in the “feel like continuing” rule. We predicted in high ruminators that there would be no significant difference between the no stop rule and “as many as can” stop rule conditions for the number of reasons generated, with both conditions generating significantly more reasons than the “feel like continuing” stop rule condition. In other words, we predicted that high ruminators would have a default “as many as can” stop rule. We made no specific predictions concerning the default rule, if any, for low ruminators.