@misc{indiciaecc8352aae9cb,
  title = {Concurrent activity under fixed-interval reinforcement.},
  author = {B F SKINNER and W H MORSE},
  year = {1957},
  doi = {10.1037/h0047021},
  url = {https://pubmed.ncbi.nlm.nih.gov/13463165/},
  note = {Source identifier: 13463165}
}