ABSTRACT
A plane is a particular type of surface and thus Donders’ law can be viewed as the more general law with Listing’s law a particular instance. In examining the validity of Donders’ law one is asking whether eye positions are confined to a surface, a question of thickness, while with Listing’s law it is a question of shape, whether the surface is a plane. The changes in shape with task may be related to the changes in thickness. In general, tasks that included more saccade directions had surfaces which were thicker than those tasks that had fewer directions. It may be that these thicker surfaces are the composites of thinner unidirectional surfaces. In addition the surface was thinnest for the Horizontal tasks, thicker for the Vertical tasks, and thicker still for the Random and Radial tasks.
