@misc{indiciae9020ec820619,
  title = {Directional selectivity and its use in early visual processing.},
  author = {D Marr and S Ullman},
  year = {1981},
  doi = {10.1098/rspb.1981.0001},
  url = {https://pubmed.ncbi.nlm.nih.gov/6111795/},
  note = {Source identifier: 6111795}
}