Fig. 4.

Conditions of a modulation test for a two-part basic object: two series of four metric variations, consisting of variations in the aspect ratio of the top part in 1 and the curvature of the axis of the bottom part in 2, two nonaccidental variations, produced by keeping constant the size of the cross section of the top part in 1 and having a straight axis of the bottom part in 2, and two rotated-in-depth versions of the basic object. When the basic object consisted of one part, the second series of metric and nonaccidental variations were along different dimensions.