Pyc, M. A., & Rawson, K. A. (2009). Testing the retrieval effort hypothesis: Does greater difficulty correctly recalling information lead to higher levels of memory? Journal of Memory and Language, 60(4), 437-447. https://doi.org/10.1016/j.jml.2009.01.004
http://memovocab.net/glossaire/glossaire_g-m/hypothese-de-leffort-de-rec.html