Mental rotation: a computationally plausible account of transformation through intermediate steps.

A critical difficulty in theories of the 'mental rotation' phenomenon has been to find a computationally plausible reason why the rotation should occur in small intermediate steps. It is pointed out that this difficulty is peculiar to metrical representations: if spatial relations are presented symbolically but nonmetrically, then the iterative or recursive application of minimal transformations is memory saving. A program ROTTER is described to illustrate this principle.