The **Cognitive Control Training** (CCT) will be operationalized using an adaptive version of the Paced Auditory Serial Addition Task (aPASAT), in which the inter-stimulus interval changes depending on the participant’s performance (Siegle, Ghinassi, & Thase, 2007). Stimuli are an auditory stream of digits (between one and nine), and an array of numbers (from one to eighteen) presented visually (on the computer screen). Participants have to continuously add up the last two heard digits and click on the corresponding sum. The CCT will be compared to a less taxing task (the **active control treatment** or ‘ACT’). Participants in the ACT have to immediately click on the number (between one and eighteen) they hear, without adding it up to the previous one. In both conditions, participants can freely plan ten sessions (of around fifteen minutes) over the course of two weeks (as long as they spread these sessions as much as possible). Before and after these ten sessions, the standard (non-adaptive) version of the **PASAT** (Gronwall, 1977) will be used to measure the effects of the CCT (on top of other indices, such as the median Interstimulus Interval over the course of the training). In order to compare both conditions, questionnaires quantifying cognitive emotion regulation strategies (**CERQ**: Garnefski, Kraaij & Spinhoven, 2001) such as Repetitive Negatitive Thinking (**PTQ**: Ehring et al., 2011), symptoms related to depression/anxiety (**DASS**: Lovibond & Lovibond, 1995) and effortful control (**ATQ**: Derryberry & Rothbart, 1988) are administered at multiple points in time (pre, post and follow-up). Additionally, participants will be asked to fill out the Credibility/Expectancy Questionnaire (**CEQ**: Devilly & Borkovec, 2000) as part of both the pre- and post-measures. For the latter case, a slightly adapted version in terms of wording is used (as it refers to an intervention in the recent past rather than in a near future). Very slight changes in the content of some of the items (pre and post) were also made to better fit the population and the nature of the CCT as an add-on intervention (a more detailed explanation of these adaptations can be found in the .txt file in the storage section of this method component). As participants are recruited in Flanders (the northern part of Belgium), the **Dutch versions** of all of these instruments are employed. On top of these standardized questionnaires, participants are also presented a list of questions measuring some basic **demographics**. There are separate and slightly different lists of demographic variables for each study under this project. The original Dutch versions as well as English translations of these lists can be found in the storage sections of the corresponding study components. The **design** of the studies is outlined in the .tif file in the storage section of this method component. Crucially, all of the measurements as well as the CCT/ACT are entirely done **online**, on a website designed specifically for (research on) CCT. Allocation to conditions is **random** and carried out automatically by the online platform, as soon as the researchers register the participant. Registration requires the participant's full name and a valid email address, both of which were provided by the participant via a contact form on the website. The participant gives his/her informed consent digitally (in addition to OR instead of physically signing a paper version of the document, depending on the study), as soon as he/she logs on to the study section of the website for the first time. Accessing this part of the website requires a password. *Derryberry, D., & Rothbart, M. K. (1988). Arousal, affect, and attention as components of temperament. Journal of Personality and Social Psychology, 55(6), 958–966. https://doi.org/10.1037/0022-3514.55.6.958* *Devilly, G. J., & Borkovec, T. D. (2000). Psychometric properties of the credibility/expectancy questionnaire. Journal of Behavior Therapy and Experimental Psychiatry, 31(2), 73–86. https://doi.org/10.1016/S0005-7916(00)00012-4* *Ehring, T., Zetsche, U., Weidacker, K., Wahl, K., Schönfeld, S., & Ehlers, A. (2011). The Perseverative Thinking Questionnaire (PTQ): Validation of a content-independent measure of repetitive negative thinking. Journal of Behavior Therapy and Experimental Psychiatry, 42(2), 225–232. doi:10.1016/j.jbtep.2010.12.003* *Garnefski, N., Kraaij, V., & Spinhoven, P. (2001). Negative life events, cognitive emotion regulation and emotional problems. Personality and Individual Differences, 30, 1311– 1327. https://doi.org/10.1016/S0191-8869(00)00113-6* *Gronwall, D. M. A. (1977). PACED AUDITORY SERIAL-ADDITION TASK: A MEASURE OF RECOVERY FROM CONCUSSION. Perceptual and Motor Skills, 44(2), 367–373. https://doi.org/10.2466/pms.1977.44.2.367* *Lovibond, P. F., & Lovibond, S. H. (1995). The structure of negative emotional states: Comparison of the Depression Anxiety Stress Scales (DASS) with the Beck Depression and Anxiety Inventories. Behaviour Research and Therapy, 33(3), 335–343. https://doi.org/10.1016/0005-7967(94)00075-U* *Siegle, G. J., Ghinassi, F., & Thase, M. E. (2007). Neurobehavioral therapies in the 21st century: Summary of an emerging field and an extended example of cognitive control training for depression. Cognitive Therapy and Research, 31(2), 235–262. https://doi.org/10.1007/s10608-006-9118-6*