Figure 1.

Sequences of visual stimulation and resulting percepts for two varieties of figure-ground displays. (Upper) Structure from motion defines a square figure region of 4° width. Initially, the display is covered with a random dot pattern; 300 ms after fixation, a brief period of motion (30 ms) occurs in which dots inside and outside of a square region move in opposite directions, each dot moving 0.06°. After the motion, the random dot pattern remains stationary and contains no physical trace of the figure. The percept obtained from this sequence of stimulation is of a square figure that persists against the static random dot pattern for approximately half a second after the motion, if fixation is maintained. (Lower) Orientation contrast defines a square figure region. Initially, the display is covered with randomly oriented line segments; 300 ms after fixation onset, these are replaced by oriented texture in which line segments inside and outside of the 4° square region are orthogonal; this remains for 500 ms. The percept obtained from this sequence of stimulation is of a square figure that persists for the duration of the presentation. In the actual displays used in our experiments, background textures subtended 28° × 21° of visual angle, and thus were in fact more extensive than the ground texture shown in these examples.