Facilitation effects with the order of presentation of the Necker cube and Schroeder staircase.

Each of 6 men and 23 women, recruited from upper division college classes was assigned to one of two conditions of viewing ambiguous figures. To Group 1 (4 men, 10 women) was presented the Schroeder stair first, then the Necker cube, while to Group 2 (2 men, 13 women) the illusions were presented in the opposite order. During 6 blocks each subject passively viewed the first figure for 3 min., followed by a 3-min. rest, and then viewed the second figure for 3 min. Subjects indicated verbally when they perceived shift. There was no significant facilitation but reversals increased when subjects viewed the same figure for a second time.