This is the data that was collected for the Double Task Switching Experiment (Hinss, Brock & Roy 2023). The File contains the behavioral as well as the subjective data of all participants. Some details: Switch 1= repetition trial 2= internal switch 3= external switch Task 1= Low/High 2= Even/Odd 3= Vertical/Horizontal 4= Cold/Hot Language (of instructions) 0= French 1= English Congruency 1= Neutral 2= Internally incongruent 3= Externally incongruent 4= Double incongruent 5= Internally congruent 6= Externally congruent 7= Double congruent Correct 1= Correct Response 0= Error Hit 0= Correct response on letter S 1= Correct response on letter L Response 0= Participants response on letter S 1= Participants response on letter L EDI (Edinburgh Handedness questionnaire) MaryA1: What time did you settle in for the night? MaryA2: What time did you fall asleep last night? MaryA3: What time did you wake up this morning? MaryA4: What time did you get up this morning? MaryB1: How was your sleep MaryB2: How many times did you wake up last night ? MaryB3: How many hours did you sleep last night? MaryB4: How many hours did you sleep during the day yesterday? MaryB5: How well did you sleep last night? MaryC1: If you didn't sleep well, what was the problem? (e.g., restless, etc.) MaryD1: How much caffine/theine did you consume today ( in cups of coffee) ? MaryD2: How much caffeine/theine would you usually have consumed at this time of the day ( in cups of coffee)? For any further questions, please refer to the full journal paper (https://doi.org/10.1371/journal.pone.0279021). For publications, please cite as: Hinss MF, Brock AM, Roy RN (2023) The double task-switching protocol: An investigation into the effects of similarity and conflict on cognitive flexibility in the context of mental fatigue. PLOS ONE 18(2): e0279021. https://doi.org/10.1371/journal.pone.0279021