Visual perception as invariance.

Abstract

The railroad tracks stretch straight and far away from me over the desert and on to the horizon. I stand squarely between them, looking along them to the horizon, and I observe both that they converge as distance gets greater and also that they are at every distance equidistant. This is the perceptual paradox of converging parallels. Every one has the experience, and Blumen-feld (1, pp. 323-346) found it under the controlled conditions of his alley'experi-ment.1 The convergence, when you have re-gard to it, is irresistible, and it is much