Mind wandering (MW) is a phenomenon in which attention is diverted from the current task and the external environment to engage in self-generated thoughts [1]. People spend approximately 10–50% of their waking hours engaged in MW, depending on the response options provided [2–7]. While it is a frequent mental activity, it tends to cause a sense of subjective unhappiness, a phenomenon that has attracted considerable attention in recent years [4].
Substantial evidence suggests that MW has dysfunctional aspects, such as those relating to negative affect or mood [4, 8–14], declining lesson performance in educational settings [15, 16], increased risk of traffic accidents [17, 18], and risk for medical errors [19, 20]; however, it has functional aspects as well, such as promoting autobiographical planning [21, 22] and creative thinking or creative problem-solving [23, 24, 25, 26], and is potentially related to emotional regulation [27, 28]. Hence, there are two opposed aspects of MW, and the factors that influence the costs and benefits of MW need to be clarified [29].
The content regulation hypothesis suggests the importance of focusing on the dimensions of MW content, such as temporal orientation and emotional valence, and that MW is either disruptive or beneficial to an individual’s health and well-being depending on its content [30]. Past orientation has been shown to follow negative affect [13], and future orientation is primarily regarded as reflecting on the utility of future planning [21] and may allow the refinement of personal goals [22]. Negative valence is associated with lower performance in working memory and sustained attention tasks compared with neutral or positive valence [31]. Moreover, research has partly shown that the combined effects of temporal orientation and emotional valence of MW may have different clinical implications. For example, past-oriented and negatively valanced thought is a form of state-level rumination that may have a dysfunctional aspect as a form of negative self-referential processing [13, 14]. In contrast, future-oriented and positive valence is a form of creative thinking and planning for the future, which may have a potential functional aspect, such as creative problem-solving and autobiographical planning [21, 27, 29, 32].
In addition, researchers have argued for the importance of distinguishing intentional and unintentional MW [33–40]. Intentional MW has been positively associated with creative task performance and the Five Facet Mindfulness Questionnaire’s subscale ‘Nonreactivity to internal experiences’, while unintentional MW has been negatively associated with them [26, 36]. Neuroimaging studies have shown that the default mode network and the frontal-parietal network have more functional connectivity with higher intentional MW traits than with unintentional MW traits [41]. Unintentional MW traits were positively associated with depression, anxiety, and stress, whereas intentional MW traits were negatively associated (albeit very weakly) with stress and anxiety and were unrelated to depression [42]. Unintentional MW is also associated with fidgeting [33], attention deficit hyperactivity disorder symptoms [43], and obsessive-compulsive disorder symptoms [44]. Intentional MW has been shown to occur more frequently in easy tasks and unintentional MW in difficult tasks [39]; additionally, intentional MW has been shown to be more future-oriented and less vague in content [45]. Thus, intentional and unintentional MW have functionally different properties and differ in their content dimensions.
We assume that the critical factors affecting the two opposed aspects of the functioning of MW would be their intentionality and content dimensions. However, the relationship of intentionality with the content dimensions has not been examined, apart from the few exceptions mentioned above [45]. In particular, the relation to the combination of different content dimensions of temporal orientation and emotional valence has never been examined. The present research question is ‘What kind of content does intentional or unintentional MW produce?’ The current study aims to examine whether intentional and unintentional MW differ in the frequency of the content related to temporal orientation, emotional valence, and their combinations. For this purpose, we used the sequential Sustained Attention to Response Task (SART) [39], a sustained attention task in which target stimuli are presented sequentially and are likely to be predictable for participants, and both intentional and unintentional MW are most likely to be induced. We assessed both kinds of MW using experience sampling with intermittent thought probes and tested the following hypotheses:
(1) Compared with intentional MW, unintentional MW is more likely to generate negative and past-oriented content and less likely to generate positive and future content.
(2) If we combine the content dimensions of temporal orientation and emotional valence, more specific relationships with intentionality are revealed.
The most common definitions of MW include task-unrelated thinking, unintentional thinking, stimulus-independent thinking, stimulus-independent task-unrelated thinking, and tortuous unguided thinking [7]. Based on the operational definition of MW as task-unrelated thoughts and for the measurement and description of the intentionality of MW, we defined MW as the self-report of thoughts unrelated to an experimental task required for participants [39, 45, 46]. Here, self-reports of thoughts unrelated to the experimental task that were generated intentionally by the participants were defined as intentional MW, while self-reports of thoughts unrelated to the experimental task that were generated unintentionally by the participants were defined as unintentional MW.