The relative roles of vertices and sides in determining perceptual centres within shapes

In the main experiment, subjects estimated the centre of five polygons in three variants: whole contour, only sides, or only corners. The perceived centre was closer to the area barycentre than to any other mathematical centre. Errors decreased as the number of sides of the figures increased. Larger mean deviations and variability were observed for the corner-only variant. Errors did not differ between the other two variants. However, this could be due to the fact that in the side-only variant only a small portion of the sides was erased, making in this way this variant to be similar to the complete contour. To exclude this possibility, in a Control Experiment side-only figures with different lengths erased around the corners were used. Since there was no worsening of the performance with longer erasings, it is concluded that, in finding the centre, the visual system relies mainly on the information provided by the sides, while a role of the corners is not evident.