@article{ref1,
title="A general gradient theory of spatial vision",
journal="Annals of the New York Academy of Sciences",
year="1962",
author="Porter, Paul B.",
volume="93",
number="17",
pages="753-759",
abstract="<p>[Abstract unavailable]</p><p>Language: en</p>",
language="en",
issn="0077-8923",
doi="10.1111/j.1749-6632.1962.tb30505.x",
url="http://dx.doi.org/10.1111/j.1749-6632.1962.tb30505.x"
}