@article{62915,
      author = {Porter, Paul B.},
      url = {http://library.usi.edu/record/62915},
      title = {A general gradient theory of spatial vision /},
      publisher = {New York Academy of Sciences,},
      recid = {62915},
      pages = {p. 753-759 :},
      address = {New York :},
      year = {1962},
}