Perceived orientation of dot patterns

Fifty subjects were asked to assign orientation to different configurations of bright dots by means of an adjustable long line. Their performance of the task clearly demonstrates that the assigned orientation of each configuration coincides with the orientation of a line drawn through the dot pattern so that the sum of the squared distances between each dot and this line is minimum. Such a line remains invariant in respect to rotation of the set of dots. It is concluded that perceived orientation of dot patterns in the plane is an invariant characteristic of this kind of visual stimulus.