1. The progress principle: Using small wins to ignite joy, engagement, and creativity at work;Amabile,2011
2. Resting on laurels: The effects of discrete progress markers as subgoals on task performance and preferences;Amir;Journal of Experimental Psychology: Learning, Memory, and Cognition,2008
3. Difficulty in videogames: An experimental validation of a formal definition;Aponte,2011
4. La loi du moindre effort mental: Les représentations mentales;Balle;Sciences Humaines,2002
5. Fitting linear mixed-effects models using lme4;Bates;arXiv preprint arXiv:1406.5823,2014