The left panel uses unfilled dots to show the positions of the full inventory of dots that marked the boundary for one of the shapes. This full inventory was never displayed. Rather, a sampling of dots, designated as the display set, was shown, using a sample size that was expected to yield recognition on approximately 75% of the trials. An example of a display set is shown by the filled dots in the right panel. For a given display, a random starting point was picked from among the list of addresses, shown by the arrow, and then every Nth dot location was selected for inclusion in the display set (with the value of N being that which would yield the number of dots needed in the display set). The size of display dots has been exaggerated for purposes of illustration.