Varied but not necessarily random: human performance under variability contingencies is affected by instructions
Learning & Behavior (2012) - Comment
pubmed: 22215413  doi: 10.3758/s13420-011-0058-y  issn: 1543-4508  issn: 1543-4494 

Alessandra S. Souza, Thaissa Neves R. Pontes, Josele Abreu-Rodrigues