@misc{indiciae9b11cc870386,
  title = {Covert reinforcement: two studies and a comment.},
  author = {J J Steffen},
  year = {1977},
  doi = {10.2466/pr0.1977.40.1.291},
  url = {https://pubmed.ncbi.nlm.nih.gov/840984/},
  note = {Source identifier: 840984}
}