Procedure

Participants completed the questionnaires in an online survey (see section “Materials”), a week before the experimental session. In the experimental session, we adopted the perceptual version of the SART from McVay and Kane (2009, 2013). Participants completed a prolonged go/no-go task and were instructed to press the space bar as quickly as possible when they see a word in lower case (e.g., “lily”) and to withhold a response when a word is printed in upper case (e.g., “BANANA”). The words were presented and masked for 0.3 s each and participants had 3.6 s in total to respond (Figure ​(Figure1A).1A). Time between trials was randomly picked from a uniform distribution ranging from 1.5 to 2.1 s. Four or five trials after the concern structures, participants were shown “thought probes”—questions probing their subjective experience. Specifically, the three questions interrogated the content, stickiness level and temporal orientation of the thoughts just preceding the probe (see Figure ​Figure1C).1C). The first question replicated McVay and Kane (2013), and pertains to the nature of the participant's thoughts just preceding the question, asking whether they thought about (1) the task, (2) task performance, (3) everyday life, (4) current state of being, (5) personal concerns, (6) day dreams, (7) other. We subsequently classified responses larger than 2 as “off-task” and responses 1 and 2 as “on-task.” The results do not change qualitatively when taking only 1 as an index of on-task. The other two questions had not been used in previous research on the current concerns task. The second question was derived from the Habit Index of Negative Thinking (Verplanken et al., 2007), and asked about how difficult it was to disengage from the previous thought and participants indicated on a Likert-Scale ranging from 1 (very difficult) to 5 (very easy) the stickiness level of the thought. The coding of this Likert scale was reversed for the analyses for ease of interpretation. The third question was similar to one used in previous mind-wandering experiments (Smallwood et al., 2011; Ruby et al., 2013), asking about the temporal orientation of the thought, i.e., whether it was related to (1) the past, (2) the present or (3) the future. After four blocks, participants were given the opportunity to take a break. The experiment ended with a debriefing, in which the participant was first asked whether they noticed anything special about the words, and then was explained the actual purpose of the experiment. None of our participants indicated noticing their concerns were embedded in the stimulus stream.