1. H. B. Barlow, C. Blakemore and J. D. Pettigrew, J. Physiol. 193, 327 (1967).
2. P. O. Bishop, The Neurosciences: Second Study Program ed. by F. O. Schmitt, ( Rockefeller University Press, New York, 1970 ).
3. J. D. Pettigrew, Nature, New Biology 241, 123 (1973).
4. J. D. Pettigrew, T. Nikara and P. O. Bishop, Exp. Brain Res. 6, 391 (1968).
5. E. W. Bough, Nature 225, 42 (1970).