We are looking for a strong and tested manipulation of mental fatigue (yes/no). Does anyone know a relatively short task (less than 30 minutes) that can do that?
You can apply cold-water test, and unsolved triangles (Baumeister, 2012), as well as keeping in mind 9.digit number during the whole experiment (Wegner, 1993). There are plenty of manipulations that provoke mental fatigue.