Thirty three subjects were tested to estimate the orientation of a dot pattern presented on a vertical screen. The subjects were asked to describe verbally the orientation of the pattern and afterwards to determine the point of intersection between the imaginary "line of orientation" of the dot pattern and a scale presented on the screen at some distance from the pattern. The subjects were inclined to give an integral description of the test stimulus such as "a constellation of dots" or "a cloud of dots" and to assign an orientation to this stimulus that corresponds to an invariant geometrical characteristics of the pattern--the line for which the sum of the squared distances to each dot of the pattern is minimum.