1. Koenderink, J. J. Vision Res. 26, 161–180 (1986).
2. Land, M. F. Nature 234, 299–300 (1973).
3. Geiger, G. & Poggio, T. Biol. Cybernet. 25, 177–180 (1977).
4. Hengstenberg, R. in The Head-Neck Sensory Motor System (eds Berthoz, A., Graf, W. & Vidal, P. P.) 49-55 (Oxford Univ. Press, 1992).
5. Strausfeld, N. J., Seyan, H. S. & Milde, J. J. J. Comp. Physiol. A 160, 205–224 (1987).