The Bactra Review
Brainchildren
J. Y. Lettvin, H. R. Maturana, W. S. McCulloch and W. H. Pitts, ``What the Frog's Eye Tells the Frog's Brain,''
Proc. IRE
47
(1959) 1940--1951, reprinted in Warren S. McCulloch,
Embodiments of Mind
(MIT Press, 1965).